LV25 drive shafts (2)

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kap all phase & 6/11/03 11:36 am Page 19 Student Workbook LV25 Drive Shafts (2) LV25/SWB Student Workbook for Technical Certificates in Light Vehicle Maintenance and Repair MODULE LV25 DRIVE SHAFTS (2) Contents Page Introduction Drive Shaft and Test Methods Common Faults: Grease leaks Noisy operation Vibration Loss of drive 7 8 Drive Layouts (Nomenclature) Features and Benefits: Advantages of four wheel drive Exercise Disadvantages of four wheel drive Advantages of rear wheel drive Disadvantages of rear wheel drive Advantages of front wheel drive Disadvantages of front wheel drive Page Traction Control: Advantages of traction control Disadvantages of traction control Progress check 9 11 11 12 12 13 14 -11 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV25 Drive Shafts (2) Issue 15 15 15 16 -22 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV25 Drive Shafts (2) Issue Introduction Drive shafts and related systems are generally very reliable However, when faults occur it is important to understand the effects that such faults will have on the vehicle and be able to recognise the symptoms Drive Shaft Inspection and Test Methods As with most diagnostic procedures, a visual inspection should be carried out first This would involve checking that the drive shaft is correctly located and all the components associated with it are in good order The areas that should be checked are the driveshaft gaitors, the constant velocity joint, the tripod, the damper and the shaft itself When carrying out an inspection on the gaiters they need to be checked for splits, cracks and correct location There is little to check with the damper other than its position, to ensure that it is not damaged and that it is securely fixed to the drive shaft -33 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV25 Drive Shafts (2) Issue The shaft itself is simply a steel tube Visually all you can is make sure it is correctly located and it is not damaged in any way Look for any signs to indicate if anything is rubbing against it such as an under body panel Although components such as under body panels are just made of plastic, the process of components rubbing against a drive shaft for long periods of time will wear a groove in the drive shaft This groove will weaken the drive shaft and make the chance of a drive shaft failure occurring more likely If further examination of the drive shaft is necessary the drive shaft will need to be removed Once it has been removed several checks should be made One of the first checks would be to measure the drive shaft run out This should be carried out by placing the shaft on two V blocks and placing a dial gauge centrally on the shaft which is then rotated through 360º Any fluctuation of the dial gauge needle indicates the drive shaft is bent The tripod should now be inspected Before it is removed from the drive shaft its orientation should be marked to ensure it fits back onto the drive shaft in the same position that it was removed from This is necessary as incorrect reassembly can lead to the drive shaft being out of balance The balls on the end of the tripod should be inspected first, they should have a smooth surface and have no signs of pitting If there are any signs of pitting they need to be replaced If pitting is present the faces that the balls run against inside the tulip will also need to be checked -44 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV25 Drive Shafts (2) Issue There are many needle rollers in between the balls and the tripod and it is possible for these to pit They should be inspected and replaced if there are any signs of pitting or overheating The old grease should be thoroughly cleaned off to make sure there are no foreign particles present in the grease This is important, as any foreign particles in the grease will lead to exaggerated wear and reduce the life of the components Upon reassembly refer to the manufacturers’ specifications to ensure the correct grease is used The position of any matchmarks should be noted, ready for reassembly At the other end of the drive shaft is the constant velocity joint This should be checked to ensure that there is no play present It should have a smooth action and no binding should occur -55 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV25 Drive Shafts (2) Issue When the joint is stripped down all of the components should be cleaned and inspected Once the components are clean it will be relatively clear if there is any unusual wear, namely pitting, although heat damage can occur (blueing and general discolouration) The shaft should be a tight fit on the inner face and there should be no backlash present If any backlash is present the worn component(s) should be replaced Upon reassembly the correct grease should be used It will normally be a grease with a high graphite content; always use the manufacturer’s recommended grease as it has to cope with high temperatures and loads that an inferior grease would be unable to If the grease degrades prematurely, component failure will not be far behind When reassembling the components on the drive shaft all the spring clips and circlips should be replaced Reusing clips greatly increases the chance of a drive shaft failure and for the small amount they cost it is well worth replacing them -66 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV25 Drive Shafts (2) Issue Common Faults Common faults associated with drive shafts and related components are grease leaks, noisy operation, vibration, and loss of drive to the road wheels Grease leaks Grease leaks from drive shafts are relatively common and split drive shaft gaiters are usually the cause They are easily identified as there are normally signs of grease on the car body or suspension arms because it sprays out due to centrifugal force and the gaiter will also be covered in grease This needs to be rectified reasonably quickly as the grease not only lubricates the joint but it also cools it If there is a substantial reduction in the available grease within the gaiter the lubrication affect will be reduced along with the cooling affect Both of these problems will lead to premature drive shaft failure Noisy operation Noisy operation is a fault more commonly associated with front wheel drive vehicles The most common noise experienced is ‘clunking’, which occurs in phase with wheel speed and is most prominent when cornering If a clunking sound is present, the outboard constant velocity joint is most likely at fault and it will need replacing It may be the case that the whole drive shaft will need replacing, as separate constant velocity joints aren’t always available Replacement drive shafts are regularly purchased from outlets on a return basis, so the old drive shaft will need to be kept -77 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV25 Drive Shafts (2) Issue Drive shafts and related components wear out over time and periodically the drive shafts of any front wheel drive vehicle will need replacing However it tends to be the more powerful front wheel drive vehicles that wear out drive shafts on a regular basis along with vehicles fitted with modified engines, as often the drive shafts are not upgraded to cope with the increase in torque Noise often precedes complete failure This tends to be when the vehicle has been driven with a split drive shaft gaiter If the gaiter is split, not only does the essential grease get displaced, but also dirt and grit can enter the area where the moving parts are Dirt and grit cause wear to occur at an accelerated rate and so it is important to make sure the drive shaft gaiters are kept in a good state of repair The clips holding the gaiters in position can occasionally break or become loose causing the gaiter to move on the shaft If this occurs, dirt and grit can access the moving parts which can lead to premature joint wear Make sure the clips are in position firmly and replace them if they are in a poor condition Ensure that good quality metal clips are fitted as it is common for plastic cable ties to be used on replacement gaiters and they are unsuitable Vibration Drive shafts can become imbalanced and this is most likely caused through bending of the shaft Vibration will be felt through the steering, clutch pedal and through the car body The vibration will increase relative to road wheel speed and is usually cured by replacement of the drive shaft, although a slight imbalance can be cured by on vehicle wheel balancing Loss of drive Drive shafts break and although is rare on standard road cars it is not uncommon on modified vehicles as they are often driven hard Revving the engine to 6000 rpm and sidestepping the clutch will take its toll! If a drive shaft has broken, there is little that can be done except replace it Drive shafts can become dislocated This is normally caused by mechanical failure although altering the suspension set-up can cause the distance between the hub and differential to increase during rebound to the point where the drive shaft pops out If this happens at high vehicle speed the consequences can be serious as the drive shaft will ‘whip’ and destroy most things in its path -88 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV25 Drive Shafts (2) Issue Drive Layouts (Nomenclature) Features and Benefits Four-wheel drive vehicles have a number of advantages over two wheel drive vehicles and fall into two main types: • • full-time 4WD (permanently engaged) part time 4WD (driver selectable) It should be noted that 4WD systems are fitted to cars of different designs for differing reasons A high performance saloon with 4WD uses the system to achieve better acceleration and handling, whereas 4WD fitted to an off-road vehicle is primarily aimed at improving the vehicles ability to cross very rough, undulating terrain A 4WD system fitted to a performance saloon is seldom suited to improving the vehicle’s ability in rough terrain and often damage can be caused if the vehicle is used this way The following points highlight the advantages and disadvantages of 4WD systems in a general sense and the suitability for use should always be taken into consideration Advantages of four wheel drive As all four wheels are driven, the chances of wheel spin occurring are considerably reduced This will lead to improved acceleration and good offroad capability In the case of off-road vehicles with differential locks, even if three wheels lose traction, providing one of the wheels has good grip the vehicle will continue to move -99 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV25 Drive Shafts (2) Issue As all four wheels are driven the tyres tend to wear evenly On two wheel drive vehicles the driven axle always wears out first, providing the suspension geometry is correct on all four wheels As engine braking can occur on all four wheels the vehicle will slow down faster as a result Vehicles with permanent four-wheel drive systems often handle better on corners This is because all four wheels are driven and can “pull” the vehicle round the corner at higher speeds, as loss of traction is less likely to occur As 100% of the vehicle’s weight is distributed over the driven wheels the system utilises the vehicle’s weight to increase the tractive effort that can be applied and as a result an improvement in handling and acceleration is achieved -1010 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV25 Drive Shafts (2) Issue Exercise Working from the figures supplied in the diagram below, complete the table for a front wheel drive vehicle: Disadvantages of four wheel drive As there are more mechanical items that need to be fitted to four-wheel drive vehicles they are often more expensive Servicing is also more expensive as there are more oils to change and more components to inspect and maintain As four wheels are driven there are more frictional losses This leads to a reduction in power at the road wheels and an increase in fuel consumption The clutch often needs replacing at more frequent intervals due to the extra loads placed on the assembly -1111 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV25 Drive Shafts (2) Issue Vehicles with four-wheel drive have more complex drive trains and so there are more things to go wrong Off-road vehicles often have a selection lever for the driver to choose whether the vehicle is driven in four-wheel drive or two-wheel drive mode Four-wheel drive should only be used off-road as drive train wind-up can occur on hard surfaces Transmission wind-up is when the front wheels have revolved at a different rate to the rear wheels and the components connecting them together (the drive train) ‘twists’ or loads up This seldom happens off-road as the tyres can slip on the soft surfaces relieving any wind-up that may have occurred If fourwheel drive is used for any substantial distance on a hard surface, serious damage can occur to the drive train often leading to costly replacement of components Additionally it has been known for injuries to occur when drive train wind-up is present and the vehicle is jacked clear of the floor (wheel free) The wind-up will release with considerable force Always ensure that four-wheel drive is disengaged (part time 4WD vehicle) before jacking up Advantages of rear wheel drive As rear wheel drive vehicles have less mechanical components when compared to four-wheel drive vehicles they cost less to manufacture (relatively) It is easier to drift a rear wheel drive vehicle round corners and in certain driving conditions this is desirable, i.e track motor racing Often a good weight distribution is achieved with rear wheel drive vehicles as the weight of the differential and drive shafts is at the rear, the engine at the front and the gearbox in the middle The handling qualities of a car that has an even 50/50 weight distribution are often superior Rear wheel drive vehicles never suffer from torque steer as all the torque is transmitted to the back wheels Disadvantages of rear wheel drive Sometimes rear wheel drive vehicles can be “tail happy” This is when the rear of the vehicle kicks out during heavy acceleration or cornering For the inexperienced driver this can lead to a spin occurring, which is obviously very dangerous -1212 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV25 Drive Shafts (2) Issue Rear wheel drive vehicles not have as high a level of traction as four wheels drive vehicles and so cannot accelerate as hard The prop shaft and gearbox in the centre of the floor pan results in less passenger compartment space Vehicles with front engine front wheel drive layouts avoid this problem The engine tends to be mounted longitudinally and so often the bonnet has to be longer or the space in the passenger compartment reduced With four wheel drive and front wheel drive it is possible to fit the engine transversally The 1932 BUCCIALI TAV12 - one of the first front wheel drive road cars Advantages of front wheel drive More passenger cabin space due to the absence of any transmission tunnel The engine can be mounted transversely which can lead to a reduced length in bonnet or increased cabin space Front wheel drive vehicles generally have good traction as the bulk of the vehicles weight is sitting directly over the driven wheels Front wheel drive vehicles often have good steering stability as the vehicle follows the thrust angle that the steered and driven wheels generate -1313 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV25 Drive Shafts (2) Issue Disadvantages of front wheel drive Poor weight distribution as the vast majority of the weight is over the front wheels only Complicated suspension and drive shaft arrangement as the driven wheels are also the steered wheels As the engine tends to be fitted transversely very large engines such as V12s tend not to be fitted to front wheel drive vehicles Front wheel drive vehicles often suffer from torque steer This is a steering snatch that occurs during acceleration due to different length drive shafts Some front wheel drive vehicles have an idler shaft fitted in the middle of the vehicle to prevent this from becoming a problem, or sometimes the longer shaft (which is more susceptible to twist) has a larger diameter Front wheel drive vehicles tend to wear out front tyres at an increased rate This is due largely to the fact that the front tyres have to cope with both steering and driving/braking forces -1414 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV25 Drive Shafts (2) Issue Traction control Traction control is an electronic system that helps to prevent wheel spin due to hard acceleration Think of traction control as the mirror image of ABS The driven wheels are prevented from spinning in the following way: • • • • retarding the ignition timing (reducing engine power) closing the throttle (reducing engine power - electronic throttles only) cutting the fuel (switching off the injectors) applying the vehicle brakes (driven wheels only) Advantages of traction control Traction control prevents wheel spin during acceleration and so relatively stable and rapid acceleration can be achieved regardless of road conditions Disadvantages of traction control Some vehicles have very good, progressive traction control systems others are less subtle With the less subtle systems, power reduction can be quite violent Sometimes traction control systems can be over sensitive leading to regular unnecessary intervention -1515 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV25 Drive Shafts (2) Issue Progress check Answer the following questions List four general methods of diagnosing drive shaft faults: Is it acceptable to re-use circlips and snap rings when rebuilding drive shafts? List the benefits of four-wheel drive (full time and part time): When driving a selectable four-wheel drive vehicle with no centre differential, should two-wheel drive or four-wheel drive be selected when driving on asphalt? Why is this? Why front tyres tend to wear more quickly on front wheel drive vehicles? What is the purpose of traction control? -1616 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV25 Drive Shafts (2) Issue ... All Rights Reserved LV25 Drive Shafts (2) Issue 15 15 15 16 -22 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV25 Drive Shafts (2) Issue Introduction Drive shafts and related... Limited 2003 All Rights Reserved LV25 Drive Shafts (2) Issue Drive shafts and related components wear out over time and periodically the drive shafts of any front wheel drive vehicle will need replacing... Rights Reserved LV25 Drive Shafts (2) Issue Common Faults Common faults associated with drive shafts and related components are grease leaks, noisy operation, vibration, and loss of drive to the