Automatic transmission service 479 Maintenance 480 Checking and changing the fluid 480 Automatic transmission fluids 482 Fluid problems 484 Extra cooling and filtering 485 Transmission adjustments 486 Brake band adjustments 490 Fault diagnosis and checks 491 Road testing 493 Diagnosing problems 496 Transmission overhaul 499 Transmission construction 499 Technical terms 500 Review questions 501
481-506_May 2chap 24 13/9/06 4:14 PM Page 481 481 Chapter 24 Automatic transmission service Maintenance Checking and changing the fluid Automatic transmission fluids Fluid problems Extra cooling and filtering Transmission adjustments Brake band adjustments Fault diagnosis and checks Road testing Diagnosing problems Transmission overhaul Transmission construction Technical terms Review questions 481-506_May 2chap 24 13/9/06 4:14 PM Page 482 482 part four automatic transmissions and drive There are many variations in the design of automatic transmissions and transaxles, and this affects the methods of dismantling and servicing However, there are some common servicing requirements and these will be covered in this chapter For particular transmissions, reference to the detailed procedures in the appropriate service manual will be necessary Checking and changing the fluid The level of fluid in the transmission is checked with a dipstick The dipstick has full-level and low-level marks and may have different levels marked for hot and cold fluid (Figure 24.1) Maintenance Automatic transmissions and transaxles require a regular check of the fluid level They also need more detailed service at regular intervals This will vary with different transmissions Some manufacturers specify service on a time and kilometre basis, for example, each three years or 60 000 kilometres, others have only a time period However, all manufacturers state that service should be carried out more frequently if the vehicle is operating in adverse conditions Where no definite service period is specified, then it is reasonable to carry out a service at every 50 000 kilometres This would be for a passenger vehicle with normal use An automatic transmission service could include draining and replacing the fluid in the transmission and converter, removing and cleaning the oil pan, cleaning or replacing the filter, carrying out adjustments to the bands and linkage and, finally, road testing the vehicle to check performance Increased power and increased under-bonnet temperatures mean that automatic transmission fluids in modern motor vehicles are subjected to increasingly severe operating conditions Therefore, regular replacement of transmission fluid is now more important than in the past Changing the transmission fluid will: remove dirt, metal particles and condensation remove fluid contaminants formed as a result of high fluid temperatures restore the correct balance of additives such as anticorrosives and detergent/dispersants Cleanliness When working on an automatic transmission, cleanliness is essential The transmission contains a large number of valves, seals and passages, and any dirt or foreign material introduced into the transmission will cause malfunction and possible damage The correct type of fluid must be used, and all containers and dispensing equipment must be perfectly clean to prevent contamination figure 24.1 Checking the level of the automatic transmission fluid MAZDA The level of the fluid is checked while the engine is idling and at normal operating temperature, and with the selector lever in the drive or park position ■ Unless the fluid level is checked by the recommended method, a false level will be indicated on the dipstick Checking the fluid level A typical method for checking the fluid level is as follows: Have the vehicle on a level floor with the transmission at operating temperature Move the selector lever through all positions and then select P Allow the engine to idle for about two minutes With the engine idling, remove the dipstick and wipe it with a non-fluffy rag or clean paper Insert the dipstick, then withdraw it immediately and check the fluid level If the fluid level is low, add the correct type of fluid to bring the level up to the full mark, but not overfill If frequent topping up is necessary, then a leak is indicated This must be located and rectified immediately, as a low fluid level will cause erratic operation and damage to the transmission Some transmissions not have a dipstick In these cases a fill plug will need to be removed from the side of the transmission to allow the fluid level to be checked and topped up if necessary 481-506_May 2chap 24 13/9/06 4:14 PM Page 483 chapter twenty-four automatic transmission service ■ When checking the dipstick, both the level and the condition of the fluid should be checked See the later section ‘Dipstick information’ Fluid change Some transmissions have a drain plug that enables the fluid to be drained without removing the oil pan (Figure 24.2(a)) Other transmissions have no drain plug and the oil pan has to be removed to change the fluid This allows additional servicing, such as filter cleaning or replacement to be carried out When the transmission is drained, fluid will also drain from the torque converter However, the transmission will not drain completely because some fluid will always remain in the lower part of the converter When removing an oil pan that has not been drained, not remove all the bolts – leave a bolt in each corner Loosen the front bolts but unscrew the 483 rear bolts a number of turns The back of the oil pan can be lowered onto the bolts so that most of the fluid can be drained before it is completely removed The oil pan will probably be stuck to the transmission case and may have to be hit with a rubber hammer to break the joint Hit the edges or corners so that the oil pan is not damaged After the oil pan is removed and before it is cleaned, it should be examined for deposits (Figure 24.3) The colour of the fluid and the amount and types of deposits in the oil pan and filter will indicate the condition of the transmission, particularly the condition of the bands and clutches figure 24.3 Checking the deposits after removing the oil pan HOLDEN LTD Most oil pans are pressed sheet steel and can distort as a result of uneven or excessive tightening If this has happened the oil pan sealing surface should be straightened before refitting Oil leaks can result if a distorted oil pan is refitted Internal filter A fluid filter is located underneath the valve-body assembly (Figure 24.2(b)) This filters all the fluid before it enters the oil pump Some filters are discarded and a new filter fitted as part of the transmission service Other filters have a fine gauze screen which is cleaned, and the filter is refitted ■ During normal operation, the fluid in an automatic transmission can reach temperatures in the vicinity of 200°C Care should be taken to avoid being burnt by hot fluid when it is being drained figure 24.2 Oil pan and filter (a) removing oil pan (b) filter bolted to the valve-body assembly HYUNDAI External fluid filter Some transmissions are provided with an external fluid filter A filter of this type is fitted to the transaxle in 481-506_May 2chap 24 13/9/06 4:14 PM Page 484 484 part four automatic transmissions and drive Figure 24.4 This is similar to an engine oil filter When carrying out a service, the filter is removed and discarded and a new filter is fitted control; heat transfer; lubrication of bearing surfaces; epicyclic gear lubrication; and friction control It has to perform all these functions while operating at very low temperatures, or at temperatures as high as 200°C oil filter torque converter dipstick Additives in automatic transmission fluids To enable an automatic transmission fluid to perform the above functions, the following additives are used: Anti-oxidants – to lengthen fluid life, permit high temperature tolerance and prevent formation of sludge and varnish Detergent/dispersants – to maintain contaminants in suspension and keep hydraulic control components and filter screens clean oil pan/cover figure 24.4 Automatic transmission with an external filter HYUNDAI Refilling the transmission Figure 24.5 shows the different levels of fluid in a transmission when it is being refilled After draining the fluid, the normal method for refilling is to add an initial quantity of fluid (approximately two-thirds the capacity) and then start the engine to allow the converter to be filled This reduces the level in the transmission The final fill is made with the engine idling, to bring the fluid level up to the ‘full’ mark Corrosion inhibitors – to prevent oil degradation products from corroding metal components Anti-wear additives – to prevent seizure of metal components under load and provide maximum protection against wear Seal swell additives – to provide control of swelling of the rubber seals to prevent loss of fluid Fluid loss can lead to overheating and transmission failure Viscosity index improvers – to maintain the correct viscosity of the fluid over a wide temperature range Pour point depressants – to permit fluid flow at extremely low temperatures Automatic transmission fluids Friction modifiers – to control the friction between the clutch surfaces, enabling smooth gear changes Automatic transmission fluid has to perform many functions such as: power transmission; hydraulic Anti-foam additives – to ensure rapid collapse of foam and rejection of any trapped air figure 24.5 Refilling a transmission (a) initial quantity of fluid (overfull) (b) after starting (underfull) (c) after topping up and checking (correct level) (d) after engine has been stopped for a period (overfull) 481-506_May 2chap 24 13/9/06 4:15 PM Page 485 chapter twenty-four automatic transmission service ■ Fluid with the correct properties is critical for ensuring smooth shifts and long clutch and band life Friction modified fluids Figure 24.6 shows the difference between a friction modified automatic transmission fluid and a nonfriction modified fluid The diagram shows that, when the speed difference between the plates is close to zero (that is, when the plates are grabbing or releasing), the frictional coefficients of these two fluids are very different The non-friction modified oil grabs harshly and releases quickly, producing a firm shift The friction modified oil grabs softly and releases softly, producing a soft shift Manufacturers design the frictional material in their transmissions to suit the recommended oil Therefore, if a type F fluid is used in a transmission which has been designed for a Dexron type fluid this will produce a bumpy or harsh shift If a Dexron type fluid is used in a transmission which has been designed for a type F fluid, then a different feel of shift could be expected This would be a particularly soft shift with the possibility of clutch plate and band slippage under full power conditions Coefficient of friction ■ Some transmission specifications exclude the addition of friction modifiers non-modified Overheating of fluid Operating conditions in automatic transmissions are more severe than in manual transmissions mainly due to the higher operating temperatures For this reason, automatic transmission fluids must be able to operate over a very wide temperature range This demands the use of a stable viscosity index improver Since the fluid must also serve as a hydraulic control fluid, relatively low viscosity base oils are used The frictional area of the transmission (mainly the bands and clutches) generates approximately 50% of the heat of the transmission fluid The other major heat source is the torque converter If excessive slip occurs in the bands and clutches, the transmission fluid will be subjected to greatly increased temperatures and these will degrade the fluid The diagram in Figure 24.7 illustrates the likely relationship between fluid operating temperature and the kilometres likely to be travelled before a transmission requires overhaul What the diagram does show is the advantage of maintaining cool fluid in the transmission 160 Thousands of kilometres Clutch packs, convertor clutches and brake bands, which are responsible for power transmission and also for the feel of the gear shifts, require fluid with these additives 485 20 C 80∞ 160∞ Transmission temperature modified figure 24.7 Graph shows the possible relationship between the operating temperature and the service life of an automatic transmission almost gripped starting to grip Sliding speed between plates figure 24.6 Comparison of friction-modified and nonfriction-modified fluids Specific types of transmission fluids There are five types of automatic transmission fluid in general use: 481-506_May 2chap 24 13/9/06 4:15 PM Page 486 486 part four automatic transmissions and drive Type F Used in Ford and Ford-type 3-speed transmissions It has no friction modifier and therefore imparts a short, abrupt shift feel to the transmission Dexron II Used in Holden and Holden-type transmissions without electronic control Gives a soft shift feel characteristic to the transmission Should not be used for extended service interval units Dexron III Supersedes all previous Holden Dexron fluids Soft shift feel Suitable for non-serviceable units and extended oil drain periods Ford 95 Fluid Specially formulated for the BTR 4-speed unit supplied for Ford Falcon and Fairlane models Gives a very soft shift feel Transmission durability is enhanced with the use of this fluid between the cooler pipes and the transmission, or the connections between the cooler pipes and the cooler Automatic transmission fluid has a distinctive colour, and this enables automatic transmission leaks to be distinguished from engine-oil leaks Figure 24.8 identifies the location of possible engine oil and transmission fluid leaks in the torque converter area of an automatic transmission Some of the fluid leaks might be cured by tightening the housing bolts; other leaks can only be cured by renewing an oil seal, an O-ring or a gasket To this, the transmission might have to be removed from the vehicle Mitsubishi M-SP Fluid Specially formulated for Mitsubishi, Hyundai and Proton transmissions fitted with a damper clutch Transmission, damper clutch performance and durability could be affected by not using this fluid ■ Always consult the manufacturer’s recommendations when selecting an automatic transmission fluid Fluid problems Some of the possible problems associated with automatic transmissions can be related to the fluid For this reason, the fluid should be one of the first things to be checked Low fluid level Low fluid level can produce many symptoms that can be mistaken for more serious transmission problems Two of the most likely causes of low fluid level are incorrect filling of the transmission during service, and external leaks However, before deciding that the transmission is low on fluid, ensure that the fluid level is being checked in the correct manner If the manufacturer’s recommendation is not followed, a false reading can easily be obtained ■ If a fluid level problem is suspected be sure that the check is being done correctly and the correct dipstick is being used Fluid leaks Oil seals and gaskets are possible sources of external fluid leaks Other possible places are the connections figure 24.8 Possible sources of oil leaks in the converter area – leaks could originate from the engine or from the automatic transmission FORD Transaxles, although of different design, could have leaks from the area of the converter or from the oil pan Leaks are also possible from the joints between the parts of the gear casing The drive-shaft oil seals, which seal between the drive shafts and the final-drive housing, are also possible places for oil leaks Internal leaks are more difficult to locate, but leaks that cause problems usually result in a loss of pressure, and this affects transmission operation Pressure tests can be carried out 481-506_May 2chap 24 13/9/06 4:15 PM Page 487 chapter twenty-four automatic transmission service Dipstick information While the dipstick is provided to measure the level of the fluid in the transmission, it can also be used to sample the fluid and provide a guide to its condition (Figure 24.9) 487 problem probably exists within the transmission, the likely one being that a clutch or band is slipping and causing overheating Particles in the fluid Fluid that is dark in colour, has a strong burnt odour and is contaminated with small particles of foreign matter, indicates problems The particles are the result of band or clutch slip and wear The discoloration is due to overheating and degradation of the fluid as well as the particles that it contains A transmission with fluid in this condition would probably require an overhaul Water contamination Water in the fluid will cause it to emulsify and turn a milky colour Water contamination is not usual, but could occur from some external source It could also occur if the cooler in the radiator was faulty The frictional material of the bands and clutch plates is attached with water-based glue If water enters a transmission it can dissolve the glue and cause the frictional material to become detached Extra cooling and filtering figure 24.9 The fluid on the dipstick is checked for level, colour and odour The fluid on the dipstick can be checked as follows Fluid colour If the fluid has its original distinctive colour, with no discolouration, it can be considered to be in good condition Discolouration indicates that the fluid is in poor condition Badly discoloured fluid indicates that there is probably a transmission problem as well Fluid odour If the fluid has a noticeable burnt odour, it will also be discoloured This indicates that the fluid has deteriorated due to overheating and should be changed If the transmission is operating properly, the fluid level is correct, and the fluid is not badly discoloured, then a change of fluid could be sufficient However, if the fluid is badly discoloured, a Degradation of the transmission fluid will shorten the life of a transmission A vehicle that has severe or heavy duty service (high loads, towing, heavy vehicle, powerful engine) can have extra cooling and filtering units fitted These help to combat degradation and so maintain the quality of the fluid Degradation of the fluid will occur by chemical breakdown due to heat and by contamination from metal particles and particles of friction materials ■ The term degradation refers to a reduction in the quality of the fluid Additional cooler Automatic transmissions are fitted with a cooler (heat exchanger) in the lower radiator tank This transfers heat from the transmission fluid to the relatively cooler engine coolant A supplementary cooler can be fitted This extra cooler will help to extend the life of the transmission fluid by maintaining it at optimum fluid temperature The additional cooler is like a small radiator (Figure 24.10) It is fitted either in front of or behind the engine coolant radiator where it can get maximum air flow 481-506_May 2chap 24 13/9/06 4:15 PM Page 488 488 part four automatic transmissions and drive The filter cannot be serviced and is discarded and replaced with a new one when the transmission is being serviced Transmission adjustments an outer container – with fins to dissipate heat Automatic transmissions and their controls are provided with adjustments These vary considerably with different makes and models of vehicle The type and method of adjustment will depend on whether the transmission has full hydraulic control, or whether it has electronic control It can also depend on whether the engine has a carburettor or electronic fuel injection (EFI) Because of these differences, and the importance of correct adjustment, it is essential that detailed information is obtained from the appropriate service manual before attempting any adjustment on a vehicle The importance of checking the basic settings and adjustments cannot be overstated – many service complaints can be rectified by attending to the items outlined below A transmission simply cannot function properly unless these are correct The following are the types of service adjustments that are generally provided on automatic transmissions: a powerful magnet – to remove fine steel particles engine idle speed a filter element – to remove foreign particles from the fluid selector cable, or linkage a bypass valve – which opens if the paper element becomes clogged throttle cable or vacuum control (for hydraulic control) inlet hose cooler outlet hose figure 24.10 An automatic transmission cooler at the front of the radiator HOLDEN LTD Additional filter Some transmissions are fitted with a replaceable fluid filter, but a supplementary filter can be fitted in conjunction with the cooler The additional filter is fitted into the cooler line, usually in the flexible line and close to the transmission cooler for easy access It is an in-line filter so all the fluid passing to the cooler first passes through the filter The filter construction is shown in Figure 24.11 It consists of: filter element magnet to attract metal particles starter isolator (neutral switch) or range switch throttle-position sensor (for electronic control) outlet hydraulic pressure brake bands Engine idle speed steel core polymer casing inlet figure 24.11 by-pass valve Magnetic in-line filter construction BOSS Idle speed is checked with a tachometer and adjusted to the rpm specified for the vehicle (usually in the vicinity of 800 rpm) Adjustment is made with the selector lever in P, and is finally checked for smooth idling in D A slight drop in engine rpm will be noticed when the selector is moved to D This is caused by the increased load on the engine High idle speed will cause creep; that is, the vehicle will move slowly as soon as a gear position is selected, even with the engine idling Creep is normal, but it will be excessive if the idle speed is too high High idle speed could also cause a band or brake to 481-506_May 2chap 24 13/9/06 4:15 PM Page 489 chapter twenty-four automatic transmission service 489 be applied harshly when the selector lever is moved to a gear position Low idle speed will cause the engine to stall There are different methods of adjusting the idle on carburettor and EFI engines, but the effects of incorrect adjustment are the same ■ For safety reasons, engine idle or any other engine adjustments should only be carried out with the selector lever in the N or P position with the park brake applied Selector cable The selector cable connects the driver’s selector lever to the manual valve in the transmission, so that whenever a gear position is selected, the manual valve will be moved to that position For the selector adjustment to be correct, the selector lever indicator should be in the N position with the manual valve also in the N position The two ends of a selector cable are shown in Figure 24.12 The selector lever and its end of the cable are shown in Figure 24.12(a) and the transaxle end of the cable and its lever arrangement are shown in Figure 24.12(b) This is a push–pull cable which enables the selector lever to move the lever on the transaxle case in both directions A threaded adjustment is provided at the selector lever This is adjusted so that the selector positions at the selector lever correspond with the selector positions at the transaxle In the design shown, a roller and quadrant are used to locate the selector lever in the various selector positions Inside the transaxle, a detent locates the manual valve in its correct positions The adjustment is made with the selector lever in N and the manual valve also in N figure 24.12 The starter isolator or neutral switch This is usually located on the transmission case (Figure 24.13) This is a safety switch, arranged to prevent the engine from starting in any gear position except N or P Incorrect operation of the switch would allow the engine to be started with the transmission in gear, causing the vehicle to move out of the control of the driver The isolator switch forms part of the starter solenoid circuit It is operated by the gear-selector mechanism to provide an open circuit in all positions except N or P This prevents the starter from operating in any other position Selector lever (a) lever and selector end of cable (b) transaxle end of cable FORD ■ The isolator switch is also called the neutral switch, inhibitor switch and sometimes the range selector switch Checking the isolator switch operation To check that the switch isolates the starter, try to start the engine with the selector lever in all positions The starter should operate in N and P only Check this while moving the selector lever backwards and forwards (within the free play) from N and also from P 481-506_May 2chap 24 13/9/06 4:15 PM Page 490 490 part four automatic transmissions and drive electrical connector range switch mounting bolts manual control lever (a) figure 24.13 Starter isolator and position switch, rotary type MITSUBISHI As a safety precaution, firmly apply the parking brake and foot brake during the check because the vehicle could move if the switch is incorrectly adjusted To check the switch itself, the harness connector will have to be disconnected at the switch and an ohmmeter used to check between the terminals at the switch connector The ohmmeter is connected between the terminals, and the switch moved to each of the gear positions adjusting nut manual control lever range switch (b) figure 24.14 Manual control lever and range switch (a) switch assembly (b) cable adjustment HYUNDAI Checking the range switch operation With electronic control, the isolator switch is also a position switch It sends signals to the ECU to tell it which position has been selected In some vehicles, the isolator switch is called the range switch An example is shown in Figure 24.14 Some vehicles have the selector positions (or range positions) shown as indicators on the instrument cluster (Figure 24.15) With this arrangement, the range selector switch is used to illuminate the position that is selected When checking the operation of the switch, the panel indicators should also be checked (a) Range indicators Throttle cable There are two cables in the accelerator and throttle cable arrangement One is the accelerator cable between the accelerator pedal and the throttle valve in the throttle body of the engine’s air intake system The other is the throttle-valve cable, which connects the throttle valve to the hydraulic throttle valve (TV valve) in the transmission To avoid confusing the two valves, the throttle valve in the air intake will be referred to simply as the malfunction indicator indicators (b) Instrument cluster figure 24.15 Automatic transmission range indicators on an instrument cluster HYUNDAI throttle valve, while the hydraulic valve in the transmission will be referred to as the TV valve 481-506_May 2chap 24 13/9/06 4:15 PM Page 492 492 part four automatic transmissions and drive late If the pressure is too low, upshifts will be early and clutches or bands could slip Vacuum control A vacuum control unit is shown in Figure 24.18 This performs a similar function to the throttle linkage figure 24.18 Vacuum-operated throttle valve line pressure, throttle pressure, throttle pressure, exhaust The unit, which is mounted on the transmission case, consists of a diaphragm in a sealed container connected by a pipe to the engine manifold The diaphragm is under the influence of engine manifold vacuum and therefore is sensitive to variations in engine load A pushrod from the diaphragm extends into the transmission and operates the throttle valve (TV valve) Changes in throttle butterfly opening and engine load will therefore affect throttle pressure, which will determine when gearshifts occur (Line pressure will also be affected.) Adjustment, if necessary, can be made either by changing the length of the pushrod between the diaphragm and the throttle valve or by turning a small screw located inside the vacuum connection Kickdown Where a throttle cable is used, the downshift valve is operated by the cable and no adjustment is required Where vacuum control is used, forced downshifts are obtained by means of a kickdown switch operated by the accelerator linkage, and a solenoid which controls a downshift valve in the transmission (Figure 24.19) When the accelerator pedal is depressed to the floor, the switch contacts are closed, the solenoid is energised and downshift pressure is provided to the shift valves to force a downshift An adjustment is provided on the switch or the linkage, and this can be altered if the switch does not operate figure 24.19 Kickdown (downshift) switch and solenoid MAZDA Throttle-position sensor The throttle-position sensor, used with electronic control, is attached to the throttle body The sensor can usually be adjusted, within limits, by loosening the screws and altering its position There are two basic types of sensors: one is a rheostat and the other is a switch The rheostat provides a voltage signal that varies with throttle opening It is basically a variable resistance, so can be checked with an ohmmeter (Figure 24.20) Its resistance should vary between closed-throttle and full-throttle positions The switch-type sensor provides signals in a number of steps It is actually a switch with a number of contacts For checking purposes, it can be treated in the same way as any other switch Brake band adjustments These are carried out to compensate for wear of the band lining A loosely adjusted band could slip, resulting in overheating and excessive wear A tightly adjusted band will cause binding, again resulting in overheating and wear Correct adjustment provides a small clearance between the brake band and the drum 481-506_May 2chap 24 13/9/06 4:15 PM Page 493 chapter twenty-four automatic transmission service electrical connector ohmmeter 493 inside the transmission The oil pan has been removed and a small tension wrench is being used on the screw adjuster In most transmissions the band is adjusted by tightening the adjusting screw to a specified torque and then backing the screw off a specified number of turns Gauge blocks are sometimes used External adjustment The adjustment shown in Figure 24.22 is an external adjustment, which is accessible after removing the outside cover from the servo plenum chamber figure 24.20 throttle body Checking the throttle-position sensor HYUNDAI This enables the band to be applied smoothly and firmly, with minimum wear occurring Some transmissions have two band adjustments while others have only one Some automatic transmissions have disc brakes instead of bands, and these have no adjustments ■ The band adjuster may be internal or external Internal adjustments can only be carried out after the oil pan has been removed Internal adjustment Figure 24.21 shows a band adjustment being carried out on a transmission; in this case, the adjustment is figure 24.22 Servo and band with an external adjustment The following is an example of how a band is adjusted: Loosen the locknut Holding the servo piston to prevent it from turning, tighten the adjusting screw to 10 Nm and then back it off Repeat this twice This is done to seat the band snugly on the drum and so prevent a false reading when adjusting Tighten the adjusting screw to Nm and then back it off 31/2 turns Tighten the locknut to 15 to 20 Nm Fault diagnosis and checks An understanding of the construction and operation of the particular type of transmission or transaxle is necessary to enable faults to be diagnosed and checks to be made While the general operating principles of most transmissions are similar, the details vary greatly figure 24.21 Servo and band with an internal adjustment MITSUBISHI ■ Vehicle manufacturers provide diagnosis guides, and these should be referred to whenever a fault is suspected 481-506_May 2chap 24 13/9/06 4:15 PM Page 494 494 part four automatic transmissions and drive Basic checks Where an automatic transmission has an operational problem, there are a number of preliminary checks that can be carried out These will provide information and possibly correct minor problems Fluid level Check the fluid level, top up if necessary and check for external leaks Fluid condition Check the fluid for deterioration and contamination readings are taken for different operating conditions (Figure 24.23) As an example, specifications for line pressure could be: 350 kPa at idle and 700 kPa at 1000 rpm These tests would be taken with the selector in D position The pressure in reverse could be up to 1000 kPa ■ Pressure readings can also be taken during road tests Engine idle Check and adjust the engine idle speed to specifications Throttle cable or linkage Check for free operation and ensure that there is no lost motion Adjust to specifications Check to ensure full throttle is available Selector linkage Check operation of linkage and starter neutral switch Electronic controls Check ECU self-diagnosis for faults Electrical connections Check all electrical connections associated with the transmission sensors for looseness or corrosion figure 24.23 Battery terminals Check both battery terminals for looseness or corrosion It is important that these checks are carried out, because the checks, and related adjustments, will correct many of the less serious operating problems ■ The checks should be made and the vehicle road tested before any internal repairs are considered In addition to the above, band adjustments can be carried out Where this entails removing the oil pan, as much diagnosis as possible should be carried out before this is done This will enable the transmission to remain operational until a decision on the problem is reached Dismantling, if considered necessary, can then be carried out Where further diagnosis is needed, a pressure test or a stall test can be carried out For a transmission with electronic control, test instruments would be used to extract self-diagnosis information from the ECU (see later sections) Pressure check A pressure check can be carried out as an aid to diagnosing hydraulic problems For this test, a pressure gauge is connected to the transmission, and pressure Oil pressure gauge connected to check the line pressure of a transaxle Stall test A stall test checks the engine, the torque converter and the transmission by measuring the maximum rpm that the engine can produce with the turbine held in a stalled condition To make the test, the vehicle is held stationary with brakes and wheel chocks, the selector lever is placed in D, and the throttle is opened fully for a very short period The test conditions are shown in Figure 24.24 A tachometer connected to the engine registers the engine rpm, and this is used to interpret engine and transmission condition As well as this, a pressure gauge can be connected to the transmission to check the system fluid pressure The tachometer reading is specified by the manufacturer, for example 1450 rpm to 1750 rpm, although these figures will vary for different engines If the tachometer reading comes within these figures, then the transmission and converter are satisfactory A low rpm reading can indicate that the engine is suffering from loss of power, a clogged exhaust, or it can be caused by a slipping stator in the converter which is placing a greater than normal load on the engine 481-506_May 2chap 24 13/9/06 4:15 PM Page 495 chapter twenty-four automatic transmission service 495 figure 24.24 Stall testing an automatic transmission chock the wheels, apply parking brake, connect tachometer, select D, apply brakes and open throttle – stall test only if allowed by manufacturer A high rpm reading can be caused by slipping bands and clutches or mechanical damage in the converter In either case, further investigation is necessary to isolate the problem Information should be obtained from the appropriate workshop manual before a stall test is attempted It should be realised that stall testing generates high fluid temperatures and places severe loadings on all parts of the transmission and drive line as well as on the engine Some manufacturers recommend against stall testing and others allow partial stall testing only A stall test should be performed only during diagnosis, and then only when permitted for the particular transmission Checks are made at different throttle openings and at different speeds, with the selector lever in different positions Road testing Smooth engagement When road testing a vehicle with an automatic transmission, checks are made of: The bands should be applied smoothly when the selector lever is moved through the various positions Reverse may be a little harsher, as higher fluid pressures are often used selector lever operation (including the isolator switch) the shift pattern (road shift speeds) the shift quality (engine overspeeding between shifts, or slippage) noise in the transmission ■ Before commencing a road test, check correct operating temperature, engine idle and fluid level General test procedures The general procedure for a road test is illustrated in Figure 24.25 During a road test, observe the following points Starter isolator switch The starter should operate only in N or P positions This is an important safety feature that must be checked Upshifts Upshifts should be checked on a level road to determine if they occur at the correct road speeds 481-506_May 2chap 24 13/9/06 4:15 PM Page 496 496 part four automatic transmissions and drive figure 24.25 Checks that can be made during a road test of an automatic transmission or transaxle Checks should be made at minimum throttle, full throttle and kickdown positions The shifts should occur at the speeds specified by the vehicle manufacturer (Refer to Table 24.1 for examples of shift speeds The table is for a transmission with a hydraulic governor.) 481-506_May 2chap 24 13/9/06 4:15 PM Page 497 chapter twenty-four automatic transmission service Downshifts Downshifts occur at lower speeds than upshifts These can be checked at closed throttle, and, where suitable conditions are available, at full or part throttle on hills to check downshifts under load Forced downshifts (kickdown) can also be checked Overdrive For transmissions with overdrive or similar switches, gearshifts can be checked with the overdrive switch both on and off With the overdrive switch off, there should be no upshifts from third to fourth gear When the switch is turned on at higher speeds, the transmission should shift from third to fourth Power and economy modes For transmissions with electronic control that have power and economy modes of operation, the shift speeds can be checked in both modes There may not seem to be much variation in road speeds, but the power indicator lamp should light with the power mode selected Shift quality The shifts should be checked for both harshness and slip This should be done under light-load and also heavy-load conditions Checks can be made both on a level road and on hills Any tendency for the engine to overspeed during shifts can also be observed Low and second positions Select 1, and check that upshifts not occur Do not overspeed in this gear Position can be selected with the vehicle stopped and then changes observed from to as vehicle speed is increased Parking pawl With the vehicle stopped on a hill, select P and release the brakes to check that the parking pawl will hold The brakes should be reapplied before moving the selector lever from the park position Reverse With the vehicle stopped, select R and check for slip and noise Some additional gear noise is not unusual in reverse Shift patterns The road speed at which the various gearshifts occur is determined by the governor (hydraulic control), the 497 road-speed sensor (electronic control) and the amount that the accelerator is depressed by the driver Road-speed checks are made at defined throttle openings In some transmissions, three positions are checked: light throttle, full throttle and kickdown Other transmissions have shift patterns specified for different throttle positions, such as quarter, half and full throttle Percentage of throttle opening is also used, for example shift speeds at 5% and 80% The shift speeds should be within the specifications for the particular transmission With hydraulic control, the shift speeds can be corrected by adjusting the throttle linkage or by altering the length of the pushrod where a vacuum control is fitted With electronic control, the shift patterns are embedded in the memory of the ECU With an electronically controlled transmission a shift-speed problem is therefore more likely to be related to the throttle-position sensor or road-speed sensor rather than to hydraulics On most transmissions the driver can alter the shift pattern by the use of a power/economy switch When the transmission is in economy mode the upshifts will generally occur earlier than they would when in power mode Adaptive Learning Strategy Some transmissions employ an adaptive learning strategy This has the capability of automatically modifying the programmed shift pattern to suit the driving habits of each individual driver This has to be considered when road testing a transmission with this feature An ECU with this program receives information from sensors which enables it to monitor parameters such as steering wheel turn, vehicle speed, throttle operation, brake operation, gearshift mode, engine rpm etc The ECU recognises the combination of these parameters as a distinctive pattern for each driver and adjusts the shift pattern to suit that individual As a simple example, a driver might use more throttle when taking off in an attempt to accelerate more quickly The ECU recognises this aspect and will delay the upshifts for that driver resulting in a quicker get-away As another example, another driver might drive cautiously when descending hills or approaching corners The ECU recognises this aspect and will change the shift pattern to earlier downshifts which slow the vehicle due to increased engine braking 481-506_May 2chap 24 13/9/06 4:15 PM Page 498 498 part four automatic transmissions and drive ■ See the previous chapter for more information on electronic control of shift patterns Table of shift speeds Table 24.1 is one example of the shift pattern for a transmission, but they can be shown in a variety of ways, including a graph The shift speeds listed for a transmission should be treated as approximate speeds, not as exact speeds ‘Light throttle’ means just sufficient accelerator movement to cause the vehicle to increase speed ‘Full throttle’ occurs when the accelerator is pressed almost to the floor, and ‘kickdown’ is when the accelerator is fully depressed In some vehicles, there is a resistance to movement between full throttle and kickdown In other vehicles, kickdown operates the kickdown switch and solenoid table 24.1 Table of shift patterns THROTTLE Light Full Kickdown Closed Full Kickdown and electronic controls must all be considered Table 24.2 shows these and indicates some of the things that might cause problems in the different locations As an example, not immediately blame the transmission for a problem that could be caused by the engine not performing properly ■ It is also possible that a faulty torque converter could cause what appears to be poor engine performance table 24.2 General location of automatic transmission problems LOCATION POSSIBLE PROBLEMS Engine Lack of power Engine needs tune-up Idle speed incorrect Torque converter Low pressure Converter lock-up clutch fault Stator OWC stuck or slipping Mechanical/power train Cables or linkage Band adjustment Band worn Clutch faulty Transmission OWC slipping Gearing damaged or noisy Hydraulic system Cable adjustment Low pressure Valves sticking Fluid leaks Leaking solenoid valve Governor or valve faulty Clutch piston Servo Electronics/electrics Isolator switch or position Sensor switch faulty or needs adjusting Electrical cable fault Connector making poor contact Road-speed sensor fault Throttle sensor adjustment or fault Other sensor fault Solenoid not operating ECU fault Loose or dirty battery terminals Low alternator output SHIFT SPEEDS (KM/H) UPSHIFT 1–2 UPSHIFT 2–3 UPSHIFT 3–4 12–20 40–45 45–55 21–30 60–70 70–90 35–40 80–90 DOWNSHIFT 2–1 DOWNSHIFT 3–2 DOWNSHIFT 4–3 10 35 20 20–25 60–70 25–30 30–35 ■ During road-speed checks, speed should be kept within the legal speed limit for the area in which the vehicle is being driven Road testing is distracting to the driver so extra care is required Diagnosing problems Workshop manuals provide diagnosis guides and charts which should be referred to whenever a problem arises These guides are often very extensive, with some providing step-by-step procedures In the event of a problem, the basic checks should be carried out, as previously discussed, so that the simpler things are checked and eliminated first If the problem has still not been cured, the more difficult things can be investigated When diagnosing an automatic transmission problem, the engine, power train, hydraulic controls A general diagnosis guide is shown in Table 24.3 This is not designed for any particular transmission However, it can be used to identify the types of problems that can occur with automatic transmissions 481-506_May 2chap 24 13/9/06 4:15 PM Page 499 chapter twenty-four automatic transmission service table 24.3 Diagnosis guide for an automatic transmission PROBLEM POSSIBLE CAUSES No starter operation in N or P Starter operates in other than N or P No engagement in D No engagement in any selector position Delayed engagement Slip or noise on take-off in D 9, 31, 41 9, 31 20, 9, 21, 24 9, 21, 16, 32, 8, 20 24, 21, 11, 31, 33, 42, 43 20, 11, 25, 16, 15, 17, 28, 36, 37 Slip or noise on take-off in 20, 11, 21, 25, 16, 15, reverse 17, 28, 36, 37 Harsh engagement all positions 1, 11, 24, 25, 23, 36, 37 Poor acceleration in first 2, 4, 14, 15, 16, 17 Poor performance and 2, 3, 30 overheating in third No 1–2 shift 6, 17, 29, 34, 36, 42, 43 Slip during 1–2 shift 20, 11, 25, 16, 17, 15, sometimes 27, 21, 36, 42, 43 Harsh 1–2 shift 11, 24, 25, 23, 36, 37, 32, 42 No 2–3 shift sometimes 9, 15, 27, 29, 34, 32, 36, 42, 43 Slip during 2–3 shift 20, 11, 24, 21, 36, 42, 43 Harsh 2–3 shift 11, 24, 23, 36, 37, 42, 43 Soft shifts 21, 16, 17, 11, 36, 37, 40 No 3–4 shift 39, 32, 15, 16, 17, 29, 32, 36, 42, 43 Shift speeds incorrect 11, 24, 28, 29, 33, 40, 42, 43 No engine braking in position 16, 17, 27 Whine in N with engine running 13 Grating noise from transmission 12, 18, 19 Knocking noise from converter 4, 5, Park will not hold 9, 12 Transmission overheating 30, 20, No converter clutch lock-up 5, 6, 8, 24 Transmission binds 27, 16, 22, 26 Engine stalls 1, Engine flare between shifts 22, 16, 17, 20, 42, 43 Vehicle has excessive creep No forced downshift 11, 38 Diagnosing electronic control problems Transmissions with electronic control have a selfdiagnosis program in the ECU which can diagnose faults as they occur during operation If a sensor or component of the electronic control system is not functioning properly, then it will send abnormal signals to the ECU When the ECU receives an incorrect signal, its self-diagnosis program recognises that the signal is not normal and records a fault in that part of the system In most cases, the information will remain in the memory of the ECU until the battery is disconnected table 24.3 499 Diagnosis guide for an automatic transmission (continued) KEY TO POSSIBLE CAUSES Engine Idle speed Lack of power Torque converter Stator OWC stuck Stator OWC not locking Converter clutch Pressure low Converter solenoid inoperative Converter damage Mechanical/power train Selector cable or linkage adjustment 10 Inhibitor switch adjustment, or fault 11 Throttle cable or linkage adjustment 12 Parking pawl or mechanism damaged 13 Oil pump worn or damaged 14 Transmission OWC not locking 15 Clutch plates worn 16 Band adjustment 17 Brake bands or plates worn 18 Gearing worn or damaged 19 Worn bearings or thrusts Hydraulic system/controls 20 Fluid level low 21 Low line pressure 22 Internal fluid leaks 23 High line pressure 24 Valves sticking 25 Vacuum control fault or leak 26 Clutch piston sticking 27 Servo piston 28 Governor valve sticking 29 Shift valves sticking 30 Cooler inefficient or line blocked Electronics/electrics 31 Isolator/selectorposition switch adjustment, or fault 32 Wiring or connectors 33 Throttle-position sensor adjustment, or fault 34 Speed-sensor fault 35 Oil-temperature sensor 36 Shift solenoid 37 Pressure-regulator solenoid 38 Kickdown switch or solenoid 39 OD switch fault 40 ECU fault 41 Anti-theft system armed 42 Loose or corroded battery terminal 43 Low alternator output The ECU provides fault information in the form of codes Depending on the system, these are obtained from it by means of a voltmeter, an LED test lamp, or specialised test equipment such as a scan tool In some cases, the transmission power-mode lamp on the instrument panel can be used for diagnosis To obtain the codes, the vehicle must have been operated so that the fault is recorded The test equipment is then connected into the system, usually by means of special connecting cables into a diagnosis connector provided for the purpose The ignition switch is turned on, but the engine is not running 481-506_May 2chap 24 13/9/06 4:15 PM Page 500 500 part four automatic transmissions and drive Diagnosis codes The codes are given numbers, and these are interpreted by the operator from the way in which the light glows, the way in which the pointer of a voltmeter flicks, or from the test instrument Specialised testers can show the code, or a pulse pattern trace, or other information on a liquid-crystal display panel LED codes Figure 24.26 shows how an LED test lamp can signal code numbers from the ECU Each flash of light from the LED represents a single digit, so code No is shown by a single flash of light which lasts for one-third of a second This is the normal condition, and code No shows that there are no faults recorded The light will flash the code again after three seconds, and will continue to so as long as the test lamp is connected figure 24.26 No 3, faults table 24.4 Diagnosis codes CODE NO NUMBER OF FLASHES MEANING 7 Normal operation, no faults Vehicle-speed sensor No Solenoid No 1, or wiring Solenoid No 2, or wiring Throttle-position sensor Shift-position switch Vehicle-speed sensor No Scan tool Figure 24.27 shows a special tester or scan tool which is used to obtain diagnosis codes and other information This is connected to the data link connector (DLC) The same tester is used for diagnosing problems in the engine’s electronic fuelinjection system and other electronic systems of the vehicle Diagnosis faults shown by an LED test lamp (a) code No 1, normal (b) codes No and DLC DAIHATSU scan tool For code No 2, there will be two flashes close together These are one second apart and are followed by a pause of three seconds before the code is repeated If there is more than one fault in the memory, a different code will follow The codes will appear in a sequence starting with the smallest number and finishing with the largest Table 24.4 is an example of the information provided by the code It shows the diagnosis code number, the number of flashes of the LED, and the part of the system that has the fault Having read the code number, the table is then used to interpret the code This table, with its seven codes, is a relatively simple one Some transmissions have many more diagnosis codes figure 24.27 Scan tool tester connected to a data link connector (DLC) to check for automatic transmission problems HYUNDAI Indicator lamp Another method of displaying codes is shown in Figure 24.28 In this transmission, the power indicator lamp is used to flash out the code number Components While the self-diagnosis tests identify the section of the system that has a fault, further testing is needed to isolate the fault to the sensor, connector, wiring or other particular part of the system A voltmeter is used to check the voltage at particular connectors, and an ... can occur with automatic transmissions 481-506_May 2chap 24 13/9/06 4:15 PM Page 499 chapter twenty-four automatic transmission service table 24.3 Diagnosis guide for an automatic transmission. .. Page 488 488 part four automatic transmissions and drive The filter cannot be serviced and is discarded and replaced with a new one when the transmission is being serviced Transmission adjustments... definite service period is specified, then it is reasonable to carry out a service at every 50 000 kilometres This would be for a passenger vehicle with normal use An automatic transmission service