Tài liệu hướng dẫn sửa chữa hộp số sàn 6 cấp cầu trước trên xe 6speed manual gearbox 02Q, frontwheel drive_Audi TT_Type_8J_MK2_Hop so san 6 cap 02Q cau truoc. Cung cấp các thông tin cần thiết cho Kỹ thuật viên tiến hành chẩn đoán, sửa chữa, đại tu nhanh chóng, chính xác, hợp lý
Service Workshop Manual Audi TT 2007 ➤ 6-speed manual gearbox 02Q, front-wheel drive Edition 04.2010 Service Department Technical Information Service List of Workshop Manual Repair GroupsList of Workshop Manual Repair GroupsList of Workshop Manual Repair Groups Repair Group 00 - Technical data 30 - Clutch 34 - Controls, housing 35 - Gears, shafts 39 - Final drive - differential Technical information should always be available to the foremen and mechanics, because their careful and constant adherence to the instructions is essential to ensure vehicle road-worthiness and safety In addition, the normal basic safety precautions for working on motor vehicles must, as a matter of course, be observed All rights reserved No reproduction without prior agreement from publisher Copyright © 2010 Audi AG, Ingolstadt A005TT00920 Audi TT 2007 ➤ 6-speed manual gearbox 02Q, front-wheel drive - Edition 04.2010 Contents 00 - Technical data 1.1 4.1 4.2 Gearbox identification Code letters, allocation, transmission ratios, capacities Transmission layout Calculating ratio “i” General repair instructions Contact corrosion! Repair instructions 1 7 30 - Clutch 12 1.1 1.2 2.1 2.2 2.3 2.4 2.5 3.1 3.2 5.1 7.1 8.1 Overview - clutch mechanism Notes on removing and installing clutch master cylinder and slave cylinder Function check for clutch master cylinder and slave cylinder Exploded view - pedal cluster, clutch master cylinder Removing and installing over-centre spring Removing and installing clutch pedal Removing and installing mounting bracket Removing and installing clutch position sender G476 Removing and installing clutch master cylinder Exploded view - hydraulics (LHD) Removing and installing pipe/hose assembly or plastic pipe Bleeding clutch system Exploded view - hydraulics (RHD) Exploded view - clutch release mechanism, slave cylinder Removing and installing clutch slave cylinder together with release bearing Clutch identification Exploded view - Sachs version clutch Removing and installing clutch (Sachs version) Exploded view - LuK version clutch Removing and installing clutch (LuK version) 12 12 13 15 16 18 21 23 24 27 29 31 33 35 36 37 39 41 45 47 34 - Controls, housing 50 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 1.10 3.1 3.2 3.3 Overview - selector mechanism Exploded view - gear knob and covers Removing and installing gear knob with gear lever boot Exploded view - gear lever and selector housing for vehicles with vehicle ID No up to 8J-7-013000 Exploded view - gear lever and selector housing for vehicles with vehicle ID No from 8J-7-013001 onwards Dismantling and assembling selector mechanism for vehicles with vehicle ID No from 8J-7-013001 onwards Removing and installing selector mechanism Exploded view - gear selector cable and gate selector cable up to model year 2007 Exploded view - gearbox selector lever and gate relay lever up to model year 2007 Exploded view - gear selector cable and gate selector cable from model year 2008 onwards Removing and installing gear selector cable and gate selector cable Adjusting selector mechanism Removing and installing gearbox Removing gearbox on vehicles with 2.0 ltr FSI turbocharged engine Installing gearbox on vehicles with 2.0 ltr FSI turbocharged engine Transporting gearbox Contents 50 52 53 55 58 59 63 68 70 72 77 79 82 82 93 99 i Audi TT 2007 ➤ 6-speed manual gearbox 02Q, front-wheel drive - Edition 04.2010 4.1 4.2 4.3 5.1 6.1 6.2 6.3 6.4 6.5 101 102 105 105 107 108 110 110 111 112 114 6.6 7.1 8.1 Exploded view - assembly mountings Removing gearbox mounting - vehicles with 2.0 ltr TFSI engine Installing gearbox mounting Removing and installing pendulum support Checking oil level in manual gearbox Securing gearbox to assembly stand Dismantling and assembling gearbox General layout of gearbox Exploded view Exploded view - gearbox housing and selector mechanism Exploded view - input shaft, output shafts, differential and selector rods Dismantling and assembling gearbox (version without circlip A for input shaft sealing cap) Dismantling and assembling gearbox (version with circlip A for input shaft sealing cap) Exploded view - gearbox housing Servicing gearbox housing Exploded view - clutch housing Servicing clutch housing 10 10.1 10.2 11 11.1 Renewing input shaft oil seal Exploded view - selector mechanism in gearbox Renewing oil seal for selector shaft Removing and installing selector shaft Exploded view - selector forks Dismantling and assembling selector forks 152 154 154 156 159 160 115 126 138 140 148 150 35 - Gears, shafts 162 1.1 1.2 2.1 2.2 3.1 3.2 Exploded view - input shaft Dismantling and assembling input shaft Modifications in area of grooved ball bearing Exploded view - output shaft for 1st - 4th gear Dismantling and assembling output shaft for 1st - 4th gear Adjusting output shaft for 1st - 4th gear Exploded view - output shaft for 5th, 6th and reverse gear Dismantling and assembling output shaft for 5th, 6th and reverse gear Adjusting output shaft for 5th, 6th and reverse gear 162 164 168 170 173 184 189 191 200 39 - Final drive - differential 205 1.1 1.2 2.1 2.2 2.3 ii Contents Renewing flange shaft oil seals Renewing flange shaft oil seal (left-side) Renewing flange shaft oil seal (right-side) Exploded view - differential Dismantling and assembling differential Table of adjustments Adjusting differential 205 205 206 210 212 216 217 Audi TT 2007 ➤ 6-speed manual gearbox 02Q, front-wheel drive - Edition 04.2010 00 – Technical data Gearbox identification The 6-speed manual gearbox 02Q, front-wheel drive is installed in the Audi TT 2007 > in conjunction with the 2.0 ltr FSI turbo‐ charged engine Allocation ⇒ page Location on gearbox ♦ Code letters and date of manufacture -arrow 1♦ Manual gearbox 02Q -arrow 2- Manual gearbox 02Q -arrow- Code letters and date of manufacture of gearbox -arrowExample: HJH 17 05 I I I I Code letters Day Month Year of manufac‐ ture (2006) Additional data identify the factory where the unit was built Note The code letters for the gearbox are also given on the vehicle data stickers 1.1 Code letters, allocation, transmission ratios, capacities Manual gearbox Code letters Manufactured Allocation from to Model HJH 6-speed 02Q JLZ KDR 05.05 06.05 Audi TT 2007 > 08.06 05.07 Audi TT 2007 > 06.07 02.08 Audi TT 2007 > Gearbox identification Audi TT 2007 ➤ 6-speed manual gearbox 02Q, front-wheel drive - Edition 04.2010 Manual gearbox Code letters HJH 6-speed 02Q JLZ KDR Engine 2.0 ltr - 147 kW FSI tur‐ 2.0 ltr - 147 kW FSI tur‐ 2.0 ltr - 147 kW FSI tur‐ bo bo bo Ratio Final drive I 71 : 18 = 3.944 71 : 18 = 3.944 71 : 18 = 3.944 for 1st to 4th gear Z2 : Z1 = i Final drive II 71 : 23 = 3.087 71 : 23 = 3.087 71 : 23 = 3.087 for 5th/6th gear and reverse gear 1st gear 47 : 14 = 3.357 47 : 14 = 3.357 47 : 14 = 3.357 2nd gear 48 : 23 = 2.087 48 : 23 = 2.087 48 : 23 = 2.087 3rd gear 47 : 32 = 1.469 47 : 32 = 1.469 47 : 32 = 1.469 4th gear 46 : 40 = 1.150 46 : 40 = 1.150 46 : 40 = 1.150 5th gear 43 : 36 = 1.194 43 : 36 = 1.194 43 : 36 = 1.194 6th gear 39 : 40 = 0.975 39 : 40 = 0.975 39 : 40 = 0.975 Reverse gear 34 : 23 x 14 : 14 = 3.990 34 : 23 x 14 : 14 = 3.990 34 : 23 x 14 : 14 = 3.990 Overall ratio iov in top gear 3.010 3.010 3.010 Gear oil capacity 2.3 litres Clutch actuation Hydraulic The following data can be found in the ⇒ Electronic parts catalogue ♦ Gear oil specification ♦ Allocation of drive shaft flange type ♦ Allocation of clutch type Manual gearbox Code letters KNX 6-speed 02Q KZU Manufactured from 02.08 06.09 to 06.09 Allocation Model Audi TT 2007 > Audi TT 2007 > Engine 2.0 ltr - 147 kW FSI tur‐ 2.0 ltr - 147 kW FSI tur‐ bo bo Ratio Final drive I 71 : 18 = 3.944 71 : 18 = 3.944 for 1st to 4th gear Z2 : Z1 = i Final drive II 71 : 23 = 3.087 71 : 23 = 3.087 for 5th/6th gear and reverse gear 1st gear 47 : 14 = 3.357 47 : 14 = 3.357 2nd gear 48 : 23 = 2.087 48 : 23 = 2.087 3rd gear 47 : 32 = 1.469 47 : 32 = 1.469 4th gear 46 : 40 = 1.150 46 : 40 = 1.150 5th gear 43 : 36 = 1.194 43 : 36 = 1.194 6th gear 39 : 40 = 0.975 39 : 40 = 0.975 Reverse gear 34 : 23 x 14 : 14 = 3.990 34 : 23 x 14 : 14 = 3.990 Overall ratio iov in top gear 3.010 3.010 Gear oil capacity Clutch actuation Rep Gr.00 - Technical data 2.3 litres Hydraulic Audi TT 2007 ➤ 6-speed manual gearbox 02Q, front-wheel drive - Edition 04.2010 Manual gearbox Code letters KNX 6-speed 02Q KZU The following data can be found in the ⇒ Electronic parts catalogue ♦ Gear oil specification ♦ Allocation of drive shaft flange type ♦ Allocation of clutch type Gearbox identification Audi TT 2007 ➤ 6-speed manual gearbox 02Q, front-wheel drive - Edition 04.2010 Transmission layout Identification Note -Arrows- point in direction of travel - Engine - Clutch - Manual gearbox - Input shaft - Output shaft II for 5th, 6th and reverse gear - Output shaft I for 1st - 4th gear - Differential Ratio Arrows point in direction of travel Rep Gr.00 - Technical data Audi TT 2007 ➤ 6-speed manual gearbox 02Q, front-wheel drive - Edition 04.2010 I - 1st gear II - 2nd gear III - 3rd gear IV - 4th gear V - 5th gear VI - 6th gear R - Reverse gear A - Final drive Transmission layout Audi TT 2007 ➤ 6-speed manual gearbox 02Q, front-wheel drive - Edition 04.2010 Calculating ratio “i” Example: Drive gear Driven gear 6th gear Final drive ZG1 = 40 ZG2 = 39 ZA1 = 23 ZA2 = 71 i = ZG2 : ZG1 1) iG = gear ratio = ZG2 : ZG1 = 39 : 40 = 0.975 iA = axle ratio = ZA2 : ZA1 = 71 : 23 = 3.087 iov = overall ratio = iG x iA = 0.975 x 3.087 = 3.010 1) Z1 = No of teeth on drive gear, Z2 = No of teeth on driven gear Rep Gr.00 - Technical data Audi TT 2007 ➤ 6-speed manual gearbox 02Q, front-wheel drive - Edition 04.2010 – Remove drive shaft (left-side) ⇒ Rep Gr 40 – Place drip tray under gearbox – Remove left flange shaft securing bolt; to so, screw two bolts into flange and counterhold flange shaft with tyre iron or other suitable lever – Pull out flange shaft and spring – Pull out flange shaft oil seal using extractor tool -T20143/2- Installing – Lightly oil outer circumference of new oil seal – Pack space between sealing lip and dust lip -arrow- half full with sealing grease -G 052 128 A1- – Drive in new oil seal as far as stop using thrust piece -3305(keep oil seal straight while installing) – Push flange shaft in towards gearbox housing and tighten to specified torque ⇒ Item 12 (page 210) The remaining installation steps are carried out in the reverse se‐ quence; note the following points: – Install drive shaft (left-side) ⇒ Running gear, front-wheel drive and four-wheel drive; Rep Gr 40 – Fill up oil in gearbox and check oil level ⇒ page 107 – Install noise insulation (centre) 1.2 Renewing flange shaft oil seal (rightside) Special tools and workshop equipment required 206 Rep Gr.39 - Final drive - differential Audi TT 2007 ➤ 6-speed manual gearbox 02Q, front-wheel drive - Edition 04.2010 ♦ Thrust piece -3305- ♦ Extractor lever -T20143/2- ♦ Drip tray ♦ Sealing grease -G 052 128 A1• Gearbox in vehicle – Raise vehicle – Remove noise insulation (centre) by releasing fasteners -1 4- – If fitted, detach heat shield for drive shaft (right-side) -arrows- Renewing flange shaft oil seals 207 Audi TT 2007 ➤ 6-speed manual gearbox 02Q, front-wheel drive - Edition 04.2010 – Remove drive shaft (right-side) from gearbox flange shaft -A- – Secure drive shafts with wire, taking care not to damage sur‐ face protection – Remove flange shaft securing bolt -arrow- To so, screw two bolts into flange and counterhold flange shaft with tyre iron or other suitable lever – Place drip tray below gearbox – Pull out flange shaft and spring – Pull out flange shaft oil seal using extractor tool -T20143/2- Installing – Lightly oil outer circumference of new oil seal – Pack space between sealing lip and dust lip -arrow- half full with sealing grease -G 052 128 A1- 208 Rep Gr.39 - Final drive - differential Audi TT 2007 ➤ 6-speed manual gearbox 02Q, front-wheel drive - Edition 04.2010 – Drive in new seal onto stop (take care to keep seal straight) Secure flange shaft with countersunk bolt -arrow- and tighten to specified torque ⇒ Item 12 (page 210) The remaining installation steps are carried out in the reverse se‐ quence; note the following points: – Bolt drive shaft (right-side) to gearbox flange shaft -A- ⇒ Run‐ ning gear, front-wheel drive and four-wheel drive; Rep Gr 40 – If previously removed, install heat shield for drive shaft (rightside) -arrows- and tighten to 25 Nm – Fill up oil in gearbox and check oil level ⇒ page 107 Renewing flange shaft oil seals 209 Audi TT 2007 ➤ 6-speed manual gearbox 02Q, front-wheel drive - Edition 04.2010 Exploded view - differential Note ♦ Mounting gearbox on assembly stand ⇒ page 108 ♦ Heat tapered roller bearing inner race to 100°C before instal‐ ling ♦ Always renew both tapered roller bearings together ♦ Adjust differential ⇒ page 217 if tapered roller bearings, dif‐ ferential cage, gearbox housing or clutch housing are being renewed - Gearbox housing - Shim ❑ For differential ❑ Determining thickness ⇒ page 217 - Tapered roller bearing outer race ❑ Pulling out ⇒ page 215 ❑ Pressing in ⇒ page 216 - Tapered roller bearing inner race ❑ Pulling off ⇒ page 214 ❑ Pressing on ⇒ page 215 - Differential cage ❑ With riveted final drive gear - Tapered roller bearing inner race ❑ Pulling off ⇒ page 215 ❑ Pressing on ⇒ page 215 - Tapered roller bearing outer race ❑ Pulling out ⇒ page 214 ❑ Pressing in ⇒ page 214 - Shim ❑ 0.65 mm thick ❑ Installation position: Shoulder on inside diameter faces towards oil seal ⇒ Item 14 (page 211) - Clutch housing 10 - Not fitted 11 - Not fitted 12 - Countersunk bolt ❑ 33 Nm 210 Rep Gr.39 - Final drive - differential Audi TT 2007 ➤ 6-speed manual gearbox 02Q, front-wheel drive - Edition 04.2010 ❑ Screws into threaded piece ⇒ Item 26 (page 211) 13 - Not fitted 14 - Not fitted 15 - Flange shaft (right-side) 16 - Protective ring ❑ Lever protective ring off flange shaft by applying a screwdriver on alternate sides ⇒ Item 15 (page 211) ❑ Press on protective ring by hand as far as stop ❑ Protective ring must engage in flange shaft 17 - Oil seal ❑ For flange shaft ❑ Renewing (with gearbox installed) ⇒ page 206 18 - Spring for flange shaft ❑ Installed behind flange shaft 19 - Thrust washer ❑ Installation position: Shoulder towards spring, lugs (if included) towards tapered ring 20 - Tapered ring ❑ Installation position: Taper towards differential cage 21 - Circlip ❑ Holds tapered ring, thrust washer and spring in position when flange shaft is removed 22 - Sun wheel ❑ Installing ⇒ page 216 23 - Differential pinion pin ❑ Drive out with drift ❑ Installing ⇒ page 216 24 - Spring pin ❑ Secures differential pinion pin ❑ Removing and installing ⇒ page 216 25 - Planet pinion ❑ Installing ⇒ page 216 26 - Threaded piece ❑ Installing ⇒ page 216 27 - One-piece thrust washer ❑ Lubricate with gear oil before installing 28 - Protective ring ❑ Lever off protective ring on alternate sides using screwdriver ❑ Installation position: Recess faces away from tapped holes in flange shaft ❑ Press on protective ring by hand as far as stop ❑ Protective ring must engage in flange shaft 29 - Flange shaft (left-side) 30 - Oil seal ❑ For flange shaft ❑ Renewing with gearbox installed ⇒ page 205 Exploded view - differential 211 Audi TT 2007 ➤ 6-speed manual gearbox 02Q, front-wheel drive - Edition 04.2010 2.1 Dismantling and assembling differential Special tools and workshop equipment required ♦ Thrust plate -VW 402♦ Press tool -VW 408 A♦ Press tool -VW 412♦ Thrust plate -40 - 105♦ Thrust plate -3005- 212 Rep Gr.39 - Final drive - differential Audi TT 2007 ➤ 6-speed manual gearbox 02Q, front-wheel drive - Edition 04.2010 ♦ Tube -3259♦ Tube -3296♦ Wheel bearing tube -3345♦ Tapered roller bearing pull‐ er -V.A.G 1582♦ Adapter -V.A.G 1582/6A♦ -1- Internal puller 46 58 mm -Kukko 21/7♦ -2- Puller -Kukko 18/1♦ -3- Splitter 12 75 mm Kukko 17/1♦ -4- Counter-support -Kukko 22/2- Exploded view - differential 213 Audi TT 2007 ➤ 6-speed manual gearbox 02Q, front-wheel drive - Edition 04.2010 ♦ Tube -VW 415 A- Pulling tapered roller bearing outer race out of clutch housing A - Counter-support , e.g -Kukko 22/2B - Internal puller 46 58 mm , e.g -Kukko 21/7– Clamp internal puller -B- firmly between ta‐ pered roller bearing outer race and shim Note After pulling out, check shim for damage and re‐ new if necessary Pressing tapered roller bearing outer race into clutch housing – First install shim • Collar on inside diameter of thrust plate -3005- faces towards outer race Pulling off tapered roller bearing inner race – Before applying puller, place thrust plate -40 - 105- on differ‐ ential cage 214 Rep Gr.39 - Final drive - differential Audi TT 2007 ➤ 6-speed manual gearbox 02Q, front-wheel drive - Edition 04.2010 Pressing on tapered roller bearing inner race WARNING Wear protective gloves – Heat tapered roller bearing inner race to approx 100°C before pressing on Pulling off tapered roller bearing inner race A - Puller , e.g -Kukko 18/1B - Splitter 12 75 mm , e.g -Kukko 17/1- Pressing on tapered roller bearing inner race • Cage with bearing rollers must rotate freely when pressing on Pulling tapered roller bearing outer race out of gearbox housing A - Counter-support , e.g -Kukko 22/2B - Internal puller 46 58 mm , e.g -Kukko 21/7- Exploded view - differential 215 Audi TT 2007 ➤ 6-speed manual gearbox 02Q, front-wheel drive - Edition 04.2010 Pressing tapered roller bearing outer race into gearbox housing – Support gearbox housing with tube -3345- directly below bear‐ ing mounting Removing and installing spring pin for differential pinion pin Removing: – Cover tapered roller bearing inner race to avoid damage and keep metal particles out of the bearing – Drive out spring pin with chisel, inserting chisel into annular groove Installing: – Drive spring pin onto stop in differential cage Installing bevel gears – Lubricate one-piece thrust washer with gear oil and install – Install both sun wheels and secure (e.g with flange shaft) – Fit planet pinions (180° apart) and pivot into position – Push differential pinion pin -arrow A- in as far as first planet pinion – Fit threaded pieces -arrows B- in sun wheels • Installation position: Stepped shoulder towards sun wheel – Drive differential pinion pin into final position and secure with spring pin 2.2 Table of adjustments Note If repairs have been carried out on the gearbox, it is only neces‐ sary to adjust the output shaft for 1st - 4th gear, the output shaft for 5th, 6th and reverse gear or the differential if components have been renewed which have a direct effect on the adjustment of the gearbox Please refer to the following table to avoid unnecessary adjustments Components renewed: Gearbox housing Clutch housing Output shaft for 1st - 4th gear 216 Rep Gr.39 - Final drive - differential Components requiring adjustment: Output shaft for Output shaft for 1st - 4th gear 5th, 6th and re‐ ⇒ page 184 verse gear ⇒ page 200 x x x x x Differential ⇒ page 217 x x Audi TT 2007 ➤ 6-speed manual gearbox 02Q, front-wheel drive - Edition 04.2010 Components renewed: Components requiring adjustment: Output shaft for 5th, 6th and reverse gear Differential cage Tapered roller bearings for input shaft Tapered roller bearings for 1st - 4th gear output shaft Tapered roller bearings for 5th/6th and reverse gear output shaft Tapered roller bearings for differential 2.3 x x x x x Adjusting differential Special tools and workshop equipment required ♦ End plate -VW 385/17♦ Universal dial gauge brack‐ et -VW 387♦ Thrust plate -VW 402♦ Press tool -VW 408 A♦ Thrust plate -3005♦ Tube -3259- Exploded view - differential 217 Audi TT 2007 ➤ 6-speed manual gearbox 02Q, front-wheel drive - Edition 04.2010 ♦ Wheel bearing tube -3345- ♦ -1- Internal puller 46 58 mm -Kukko 21/7- ♦ -4- Counter-support -Kukko 22/2♦ Dial gauge -VAS 6080- ♦ Dial gauge extension, 30 mm ♦ The differential must be re-adjusted when the following compo‐ nents have been renewed: ♦ Gearbox housing ♦ Clutch housing ♦ Differential cage ♦ Tapered roller bearings for differential Table of adjustments ⇒ page 216 218 Rep Gr.39 - Final drive - differential Audi TT 2007 ➤ 6-speed manual gearbox 02Q, front-wheel drive - Edition 04.2010 Adjusting: Note The tapered roller bearing inner and outer races are paired Do not interchange – Press tapered roller bearing outer race with shim (0.65 mm) into clutch housing • Collar on inside diameter of thrust plate -3005- faces towards outer race – Press tapered roller bearing outer race without shim into gear‐ box housing – Install differential in clutch housing – Fit gearbox housing and tighten bolts to specified torque ⇒ Item 11 (page 112) and ⇒ Item 12 (page 112) – Press differential towards clutch housing; hold in this position and turn eight times – Press differential towards gearbox housing; hold in this posi‐ tion and turn eight times – Attach dial gauge -VAS 6080- and set to “0” with a preload of mm A - Dial gauge extension, 30 mm – Move differential up and down and note play indicated on dial gauge (in this example: 0.70 mm) Determining thickness of required shim: The specified bearing preload is obtained by adding a constant figure (0.25 mm) to the reading indicated Example: Measured value + Preload (constant value) Thickness of shim = 0.70 mm 0.25 mm 0.95 mm Exploded view - differential 219 Audi TT 2007 ➤ 6-speed manual gearbox 02Q, front-wheel drive - Edition 04.2010 – Take off gearbox housing – Pull tapered roller bearing outer race out of gearbox housing A - Counter-support , e.g -Kukko 22/2B - Internal puller 46 58 mm , e.g -Kukko 21/7– Select a shim of the required thickness from the table For part numbers refer to ⇒ Electronic parts catalogue – Insert shim of correct thickness The following shims are available: Thickness of shims in mm 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 1.05 1.10 1.15 1.20 1.25 The exact shim thickness required can be obtained by combining shims of different thicknesses If the size of the shim required is larger than those listed in the table, install two shims amounting to the correct value Insert the thicker shim first – Press outer race in again and tighten gearbox housing bolts to specified torque ⇒ page 112 220 Rep Gr.39 - Final drive - differential