BMW e46 M3 SMG to Manual Swap

The E46 SMG does well on the track for DE and Time Trials but for racing it is not quite ideal. It is streetable technology and hinders the car in various ways on the race track. Up shifting is a touch slow and down shifting doesn’t perfectly rev match creating a problem on trail braking and turn entry. You can overcome this somewhat by assisting rev matching by bliping the throttle but it is still not ideal. Another problem is transmission longevity. The 3rd gear syncros in the 6 speed transmissions are known to fail quickly. However, the 5 speed ZF is known to be a tough transmission and they are readily available from junk Yards. The 5 speed gear ratio’s are the exact same as the 6 speed ratios for 1st through 5th gear. Basically 6th gear is pretty much not used on the track. Some have tried to use a really short diff to utilize 6th gear but the pinion in the diff becomes too small and breaks teeth. Since 6th gear is useless it makes sense to go to a lighter, cheaper, more durable 5 Speed transmission.

So if you want to switch to a 5 speed gear box below is complete documentation on how to do this. Also note, if you are going to build a car from scratch, having the ability to include an SMG car in your donor car search is a nice option knowing the swap is easy.

Special Notes

• Parts such as the clutch disk and shift lever can be different depending on your needs but the general information is logged in the tables below.

• You will need to weld a rear shift carrier bushing bracket to the chassis. Part (41128246251) You could actually bolt this part in if you drilled holes but some spot welding is best. Another option is to omit the bracket and bushing and use a rod end bolted to the chassis with an adapter sleeve to mate the rod end to the shift carrier.

• You will need to trim the clutch fluid supply nipple on the brake fluid reservoir. This is simple with a pair of diagonal cutters.

• You will have left over SMG wiring that will need to be removed. It is loomed with other engine wires so it is a pain to remove. You could get a Non SMG engine wire harness and rewire the whole engine. It is a toss up.

Transmission/Clutch/Driveshaft

Shifter Parts

Clutch Pedal and Hydraulics

Recommended Replacement Parts

Internal Clutch Parts

Electrical

The SMG DME software DOES NOT look for a clutch switch input to the EWS module, it uses logic from the SMG computer. When switching to a Manual shift DME, the software DOES looks for a clutch signal from the EWS. This creates a problem since the e46 M3 SMG chassis wire harness doesn’t have the wiring that goes from the clutch pedal switch to the EWS module. Since we are talking about a racecar the best way to do this is to run a fake signal to the EWS module. You can do this by supplying +12v to Pin 8 on the EWS plug. Since there isn’t a pin or wire there, you can steal a pin out of the plugs for the SMG computer or buy a new pin from BMW and wire it yourself. The +12v supply can come from various places such as the ignition switch, power distribution block, brake switch or even a switch on the dash. The nice thing about this is you can use the starter to move the car in an emergency since you do not have to have the clutch pedal depressed.