The E46 M3 had a couple major issues, one of the lesser ones is the SMG gearbox. The hydraulic pump often fails resulting in a costly repair. If this happens to a car you own it often make sense to convert the car to a manual rather than fix the SMG unit. Manual E46 M3’s tend to be more desirable and cost quite a bit more than manual M3’s so often times owners can buy an E46 M3 SMG and have it converted to manual for about the same price as buying a true manual.
Since the SMG transmission and the 6 speed transmission are internally identical all that is required to physically do this swap is to modify the bellhousing on the SMG transmission. This modification adds in the shift detents so the driver can feel where the gears are. Since the SMG is shifted by the computer these detents were not necessary in the manual gearbox. Machining the bell housing accurately is critical so that the driver can easily find the gears. If the machine work is not precise then the driver can have trouble finding gears as the gates will not be in the correct location. We’ve seen this problem on some swapped cars that have ended up at our shop for troubleshooting.
Here’s a video collecting the informational videos given to BMW Dealerships circa 2001
For race cars it is also possible to swap the 6 speed transmission to a less expensive and rebuildable 5 speed transmission. Coupled with a 3.91 or 4.10 final drive this is often a good race/track setup, but it does require modifying the driveshaft and shift linkage. Overall the cost tends to be about the same as the 6 speed conversion but the 5 speed also has a considerable weight advantage compared to the 6 speed.
This swap also requires the installation of a clutch pedal, master cylinder, and slave cylinder into the car. In addition, the transmission tunnel must be opened up to allow the shifter to be installed. A shifter bushing carrier also has to be installed into the car if a factory style shifter is to be used. Since the transmission will be removed this is also the perfect time to change out that worn out clutch and flywheel.
In order for cruise control, PDC, and the reverse light to function the car must be wired and re-coded as a manual car. The SMG computer is removed and all SMG components are unplugged. The clutch switch and brake switch must be installed and wired appropriately to retain the function of a true manual transmission E46 M3. We also have a special tune for the SMG to Manual conversion, developed by Frank Smith, that adjusts the idle to the correct level and can be coupled with a performance tune upon request.
If you’re considering an SMG to Manual conversion and are near the Orange County, CA area we encourage you to contact us for a quote.