Volvo M90 transmission
M90 is the model designation for an automotive rear-wheel drive gearbox that is found in Volvo 940/960 models from 1994-on.
The gearbox is made by Getrag in Sweden and it is of a 3-axle design, deriving from the Volvo M56 gearbox of the front wheel driven 850 series. It is rumored that the gears between these gearboxes can be swapped.
There are three variations of the gearbox. There is a version for the cast iron 4 cylinder engines of the 940 (redblock), the all aluminum 6 cylinder of the 960 (whiteblock), and the version for the Volkswagen 6 cylinder diesel engine D24TIC. The differences are the bell housing bolt pattern and the output shaft flange with a 3-bolt flange for the redblock/diesel engines and a 4 bolt flange for whiteblock engines. The variant for the 6 cylinder Volvo engine will fit on all 4/5/6 all aluminum Volvo N/RN-series engines.
The clutch is hydraulically operated by a master/slave cylinder setup with a normal clutch fork and throw out bearing. The flywheels used with these gearboxes are dual mass versions (petrol engines) to eliminate the noise that 3-axle (3-shift) gearboxes can make in neutral, and a regular (single mass) flywheels for the diesel engine.
All gears, including the reverse gear, are synchronized.
The M90 gearbox is available with different gear ratios.
| Gear | M90H1 | M90H2 | M90L1 | M90L2 |
|---|---|---|---|---|
| 1 | 3.54:1 | 3.54:1 | 3.91:1 | 3.91:1 |
| 2 | 2.05:1 | 2.05:1 | 2.20:1 | 2.20:1 |
| 3 | 1.38:1 | 1.38:1 | 1.38:1 | 1.38:1 |
| 4 | 1.00:1 | 1.00:1 | 1.00:1 | 1.00:1 |
| 5 | 0.81:1 | 0.70:1 | 0.81:1 | 0.70:1 |
| Reverse | 3.00:1 | 3.00:1 | 3.00:1 | 3.00:1 |
This gearbox is the strongest manual transmission that Volvo fitted to their rear wheel drive cars. The H2 and L2 versions are stronger than the H and L versions. There is a common disbelief that H is stronger than L, but the only difference between H and L is the gear ratio. In 1997, M90 H2 and M90 L2 where introduced. This revised model of the M90, had an improved design of the 3rd gear synchronous ring; to prevent premature failure of the transmission.
It is possible to modify the synchronous ring of the M90 H and M90 L gearboxes, to eliminate the problem. To do so, one must open up the transmission and weld the synchronous ring in its place.
External links
For applications over 350 horsepower one should consider the BWM Getrag 265 or ZF transmission. Retrofitting another manufacturers transmission requires a modification to the 'bell housing' (an adaptor-plate from KLRacing can also be used). This will require a custom drive shaft and modifying the gear linkage length (depending on vehicle application).