BMW Coupes and Sedans 1970-1988 Repair Guide

4-Speed Transmission Overhaul

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See Figure 1



Click image to see an enlarged view

Fig. Fig. 1: Cross-sectional view of a 4-speed transmission

DISASSEMBLY



  1. Mount the transmission securely in a transmission stand or other suitable device.
  2.  
  3. Remove the console from the transmission.
  4.  
  5. Remove the clutch release bearing assembly and release lever from the front of the transmission.
  6.  
  7. Remove the front guide sleeve and retaining bolts. Do not lose the shims.
  8.  
  9. Remove the circlip and shim from the input shaft.
  10.  
  11. Remove the case cover mounting bolts and drive out the 2 dowel pins from the case cover.
  12.  
  13. Using a special case puller or equivalent, remove the cover from the transmission.
  14.  

The input shaft bearing will remain with the case cover during removal.

  1. Remove the front bearing from the case cover by driving it from the rear to the front. Do not lose the accompanying shim.
  2.  
  3. Remove the lockpin and spring from the case.
  4.  

The lockpin maintains the selector shaft positioning.

  1. Move the 3rd/4th selector lever and rod to the 3rd speed position. Drive the fork retaining pin downward until rod can be pulled out.
  2.  

The fork retaining pin must be driven downward between the teeth of the synchronizer body. The pin should remain in the lower part of the selector fork.

  1. Slide the locking sleeve away from the pin of the selector shaft coupler and drive the pin from the coupler.
  2.  
  3. Remove the selector rod by pulling it forward and out of the shifting fork.
  4.  
  5. Move the gear sleeve back to the neutral position and remove the selector fork.
  6.  
  7. Remove the bushing and the speedometer driven gear.
  8.  
  9. Straighten the bend in the lockplate on the output flange retaining nut. Install a flange holding tool and remove the locknut. Pull the flange from the output shaft.
  10.  
  11. Remove the rear bearing support ring and shims.
  12.  
  13. Using a special bearing puller or equivalent, remove the rear bearing from the transmission cover.
  14.  

A 0.08 inch (2mm) metal strip must be placed between the 2nd and 3rd gears to prevent the pressing off of the 2nd gear synchronizer body during the removal of the rear bearing from the shaft and cover.

  1. Lift the input and output shaft assemblies slightly and remove the countergear assembly from the end bearing and out of the cover.
  2.  
  3. Pull the selector fork, the reverse gear and the selector rod from the transmission cover. Do not lose the detent balls.
  4.  
  5. Remove the input and output shaft assemblies, align with the 1st/2nd selector rod and fork, from the transmission cover. Do not lose the detent balls.
  6.  
  7. Remove the reverse light switch and the end cap for the 1st/2nd selector shaft.
  8.  
  9. Remove the input shaft from the output shaft and remove the 4th speed synchronizer (baulk) ring.
  10.  
  11. Remove the circlip from the front of the output shaft and remove the support disc, synchronizer body assembly, 3rd gear synchronizer (baulk) ring, needle bearing race and the 3rd gear from the shaft.
  12.  
  13. Place the output shaft into a press or equivalent and remove the speedometer drive gear, washer, reverse gear, spacer, needle bearing race, 1st gear, synchronizer (baulk) ring, synchronizer body with the sliding sleeve, synchronizer (baulk) ring, needle bearing race and the 2nd speed gear from the shaft.
  14.  
  15. The 3rd and 4th gears can be pressed from the countershaft gear assembly, along with the roller bearing.
  16.  
  17. The pilot bearing can be removed from the bore of the input shaft.
  18.  
  19. The synchronizer unit can be disassembled by sliding the sleeve off the hub. The pressure pads will drop from the unit as the sleeve is removed.
  20.  
  21. Replace all worn, damaged or broken parts, along with new gaskets and seals.
  22.  

ASSEMBLY



Measurements Prior to Transmission Assembly

Washer type shims are used to control the end-play of the shafts and gears, while maintaining gear positioning, so that tooth contact is in proper relationship with each other. It is most important to inspect, measure and correct the shim packs to obtain the necessary preloads and clearances.

INPUT SHAFT

See Figure 2

  1. Install a 0.04 inch (1mm) shim and the ball bearing into the case bore.
  2.  
  3. With a depth gauge, measure the distance, from the sealing surface of the case to the surface of the bearing race.
  4.  



Click image to see an enlarged view

Fig. Fig. 2: Measurements needed to determine shim thickness

  1. A numerical figure is electrically engraved on the input shaft and represents column B in the shim chart.
  2.  
  3. The thickness of the shim needed on the input shaft can be determined by corresponding the measurements to the chart and locating the proper shim.
  4.  

COUNTERSHAFT ASSEMBLY
  1. Measure the distance from the sealing surface of the case housing to the circlip in the bottom of the housing.
  2.  
  3. Install the countershaft into the transmission case bearing and measure the distance from the top of the large bearing race to the sealing surface of the case, with the gasket installed.
  4.  
  5. Determine the thickness of the shim by subtracting the distances. The result is shim.
  6.  

These shims can be used to change tooth engagement.

SPEEDOMETER GEAR-TO-TRANSMISSION CASE
  1. Measure the thickness of the speedometer gear.
  2.  
  3. Press the ball bearing into the transmission case and measure the distance from the sealing surface of the case to the race of the bearing, without the gasket installed.
  4.  
  5. The nominal distance is a predetermined distance and is used to arrive at the proper sized shim.
  6.  
  7. Subtract the measured distance from the nominal distance. Subtract this valve from the measured distance between the ball bearing to the transmission case to determine the proper sized shim to be used between the speedometer gear and the ball bearing of the case.
  8.  

Gear Assembly
  1. Install the synchronizer springs onto the hub with the hooked ends of the springs in different pressure pads.
  2.  
  3. Install the pressure pads in place, then slide the sleeve with the flat teeth locations over the pressure pads.
  4.  
  5. If the 3rd and 4th gears have been removed from the countershaft, reinstall or replace the gears back on to the shaft. Heat the gears to 250-300°F (120-150°C) and install. The high collar on the bore of the 3rd and 4th gears should face the 2nd gear. Install the bearing and race onto the shaft.
  6.  
  7. Place the output shaft in an upright position with the rear of the shaft up. Place the 2nd speed gear and needle bearing assembly onto the shaft. Install the 1st/2nd synchronizer assembly with the 2 synchronizer (baulk rings onto the shaft, followed by the 1st speed gear, needle bearing, spacer, reverse gear wheel, washer and complete the assembly by pressing the speedometer gear onto the shaft.
  8.  

The end-play of the gear train should be 0.003 inches (0.08mm). Adjust by changing the selective washer between the speedometer gear and the reverse gear.

  1. Invert the output shaft and install the 3rd gear onto the shaft. Install the synchronizer assembly less the 4th speed synchronizer (baulk) ring onto the shaft and retain with the support disc and circlip.
  2.  

Case Assembly
  1. Have the transmission case mounted in a secure support.
  2.  
  3. Insert the selector rod detent balls and springs. Install the reverse gear selector rod and reverse gear, into the case until the 1st lock is engaged.
  4.  
  5. Install the countershaft into the roller bearing, mounted in the case.
  6.  
  7. Install the input shaft on the output shaft and install the assembly into position on the transmission case.
  8.  
  9. Install the predetermined shim between the speedometer gear and the ball bearing. Install the bearing into the case, but do not seat completely.
  10.  
  11. Using a special bearing installer tool or equivalent, seat the bearing on the output shaft and into the transmission case.
  12.  
  13. Check the tooth engagement of the input, output and countergear assemblies. Tooth engagement can be changed by movement of shims.
  14.  
  15. Install the speedometer bushing and driven gear.
  16.  
  17. Set the transmission assembly in the upright position with the output shaft pointing upward. Measure the distance from the case to the ball bearing race.
  18.  
  19. Measure the distance from the shoulder height of the sealing cover, to the surface of the gasket on the cover.
  20.  
  21. Subtract distances from Step 9 and Step 10. The result is the thickness of the needed shim between the ball bearing and the sealing cover.
  22.  


WARNING
There should be no end-play between the ball bearing race and the sealing cover. Measure and remove play with shims.

  1. Secure the sealing cover and install the output flange. Install the locknut and washer. Place the lockplate washer into the groove of the flange.
  2.  
  3. Install the 1st/2nd gear selector rod and fork into place. Insert the locking detent balls and springs. Secure the fork to the rod with the rolled pin.
  4.  
  5. Install the 3rd/4th selector fork into place on the sliding sleeve. Install the main selector rod. Install the lockpin and spring into the tapered bushing. Install the locking detent balls and springs.
  6.  
  7. Install the 3rd/4th gear selector rod and secure to the fork with the rolled pin.
  8.  
  9. Install the reverse light switch and the selector rod cap.
  10.  
  11. Install the gasket on the mating surfaces of the transmission case and housing. Install the predetermined shims on their respective locations and install the transmission housing over the gear assembly.
  12.  
  13. Bolt the housing to the case securely.
  14.  

It may be necessary to heat the transmission area of the input shaft to install the front bearing.

  1. Install the shim and bearing onto the input shaft and housing. Install the washer and circlip.
  2.  
  3. Install the clutch release guide sleeve and a shim to eliminate any existing play between the guide and the bearing.
  4.  
  5. Measure the distance between the case and the ball bearing. Measure the distance from the top of the shoulder of the guide sleeve to the mating surface, with the gasket installed.
  6.  
  7. Subtract the distances, and the result is the thickness of shim needed to remove the existing play between the guide and the bearing.
  8.  
  9. Install the selector rod coupler and secure with the pin. Slide the sleeve over the pin.
  10.  
  11. Install the console onto the transmission case.
  12.  
  13. Fill the unit with the proper level of gear oil.
  14.  
  15. Install the clutch release bearing assembly and the operating lever.
  16.  
  17. Install the crossmember and the exhaust system bracket.
  18.  

 
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