Gearbox types

Overdrive 5-speed, click to enlarge

Available gearboxes on E21’s were the Getrag manual units and  ZF automatics. Standard equipment on most models was a 4 speed manual. Overdrive 5 speed was optional and became standard equipment on some top of the range models in later years (1981-1982). There was also an optional close ratio 5 speed gearbox with a dogleg pattern and a 1:1 (prise direct) 5th gear for more sporty characteristics. The 5 speed gearboxes can be distinguished from the 4 speeds easily as they have an extended housing at the rear. The ZF 3HP-22 auto box has 3 gears.

Sports 5-speed, click to enlarge

Because of limited availability of the 5 speeds boxes, a frequently asked question is if there are gearboxes from other models that are a straight swap. Because of the mechanical speedometer drive that is required for the E21, the choice is limited. First, the gearbox needs to be for the same engine type, i.e. M10 OR M20. On top of that it needs the mechanical speedometer drive as well. This means that only E12 M10 and M20 gearboxes can be used and sadly they’re just as rare as E21 five speed gearboxes.

Please note that M10 and M20 gearboxes are not interchangeable and that the much more common E30 gearboxes do not have the mechanical speedo drive.

When you are planning to buy a 5-speed for conversion, it is advised to buy a complete kit from a wrecker. Since the 5 speed gearbox is longer, the propshaft is shorter and there are two different connections between box and shaft (3 lug and 4 lug). The steel plate holding the gear change mechanism and the connecting rod are also shorter as the shifter axle is closer to the driver now. So it is better to buy a box complete with propshaft and shifter mechanism.

Gearboxes factory fitted in E21’s:

 316-318-320/4 > 08 / 77 Getrag 242/9 or 242/18
 316-318-320/4 08 / 77 > Getrag 242/18.30
 320i   Getrag 242/18
 320/6-323i   Getrag 242/7-50
5-speed sports    
 318-318-320/4-320i > 81 Getrag 245/2
 315-316-318i 81 > Getrag 245/10 BO
 320/6-323i 81 > Getrag 245/11 OO BJ
5-speed economy (overdrive)   
 315-316-318-318i   Getrag 245/4 BN
 320/6-323i   Getrag 245/288 GC
Automatic gearbox (3-speed)  
 all models   ZF 3 HP-22

Additional info on codes on top of gearbox casing:

T or BO -> m10 Getrag 245 CR
BJ or GJ -> m20 Getrag 245 CR
BN,GH or GL -> m10 Getrag 245 OD
GC,GG or GM -> m20 Getrag 245 OD
ME,MF -> m10 Getrag 240 OD
MG -> m20 Getrag 240 OD
CR = “sport” and OD = overdrive

Gear ratios        
  4-sp 5-sp sports 5-sp economy automatic
1st 3.764 3.764 3.682 2.478
2nd 2.043 2.325 2.002 1.478
3rd 1.320 1.612 1.330 1.000
4th 1.000 1.229 1.000
5th 1.000 0.805
reverse 4.096 4.096 3.682 2.090

Short 5-speed!

Thanks to member Kyle Summerfield we were also made aware of the fact that on the very latest 1982-1983 models, at least the M10 4 cylinder versions, a different manual eco 5-speed gearbox was applied as well. This gearbox cannot be recognized by its extension, it is in fact a few cm’s shorter than the regular 4-speed!

Best way to check is to test out the shift pattern, just keep in mind this is mirrored if the complete switcher mechanism is missing so reverse gear can easily be mistaken for 5th gear… you won’t be the first to take a 4 speed home for way too much money!

This gearbox appears to be numbered 240.0.0266.90.

Short rear end with speedo drive

Compared: regular 5-speed on the left, later short 5-speed on the right

Click here for a detailed topic on 6 cilinder gearboxes on the forum