BMW gearbox: Splines and other information

Easily compare BMW gearboxes with each other

1. What do the letters mean?
2. BMW gearbox numbers
3. Clutch release bearing
4. Gear shift problems
5. Compare Release bearings

What do the letters mean?

What is the difference between the different letters / designations HGD / JGA / HGU / JGG?

• HGD / JGA
  These gearboxes have a "regular" input shaft located in a support bearing in the flywheel.
• HGU
  These gearboxes have a hole in the input shaft so an adapter is required between the support bearing and the input shaft. An adapter is used so that the input shaft of the gearbox will be supported / fit in the support bearing in the flywheel.
• HGA
  These gearboxes have the same input shaft as the HGD but with a different bell housing (Old BMW M50 style)
• JGG
  This gearbox comes from the BMW 123d.
• JGK / HGX (GS6-53BZ)
  Gearboxes from N54 engines
  

BMW gearbox numbers

• GS6-53DZ = 26x35mm
• GS6-53BZ = 26x35mm
• GS5-39DZ = 10x35mm
• GS6-37DZ = 22x29mm
• GS6-37BZ = 22x29mm
• Getrag 420 TBAI = 10x35mm
• S5D-310 ZF-310 = 10x29mm
• S5D-250 = 10x29mm
• S5D-320 ZF-320 = 10x29mm
• Getrag 420 TBAB = 10x29mm
• GS7D36SG = DCT / DKG
• 8HP70

Clutch release bearing

215-240mm
BMW gearboxes use two different release bearings. 35 and 29mm. These are made for 215-240mm pressure plates = Inner diameter of the pressure plate spring.

184-200mm
If a 184-200mm clutch is used, a smaller release bearing is needed = A bearing that is adapted for a smaller pressure plate spring.

Below is a list of release bearings that fit BMW ZF and Getrag gearbox input shafts:

10 splines / 29mm axle - 184-200mm / 215-240mm
10 splines / 35mm axle - 184-200mm / 215-240mm
22 splines / 29mm axle - 184-200mm / 215-240mm
26 splines / 35mm axle - 184-200mm / 215-240mm

Gear shift problems

If a Gearbox, regardless of Getrag or ZF, is challenging to shift, a few things affect it.

Clutch
It could be air in the clutch cylinder (slave or master cylinder) that causes the clutch not to disengage correctly, which can lead to a hard-to-shift box and also scratches when shifting. This air is harmful to the gearbox and needs to be looked into immediately.

When this problem occurs, bleed the clutch hose! If this helps but slowly worsens, a clutch cylinder is probably bad and leaks air into the system. Then replace this and repeat the procedure.

If the above does not help and it is still slow to shift, then an adjustment of the linkage or cables can help. If these do not reach their full stroke, shifting problems can occur.

Synchronizer rings
If you can shift properly but one or more gears are difficult to engage or you hear scraping noises, this must be addressed immediately as this is harmful to the gearbox. Most likely, it is the synchronization rings that are worn or have some other fault. Step one is now to change the gearbox oil. If this does not help, the sync rings must be replaced to fix the problem.

Most often, problems with the synchronization rings appear when the parts spin faster / at higher RPM.

Gear jumps out
If the gear jumps, the gear fork in the gearbox may be bad. The solution is to change the shift fork / shift fork.