final drive swap

[daddyo8]

I'm thinking of swapping my final drive out of my 93 325i (automatic) into my 94 325is (standard). Considering the gear ratio difference, how will this change my drive, like mpg, acceleration, mph readout accuracy, engine load, etc.
Any educated guesses out there in forumland?

[Willyum]

If you don't change the differential to match, you won't get the drive performance you are expecting. Years ago I changed an automatic to a three speed O.D. setup. I found later, after I was away from where I could get the differential swap, that the car barely had enough power to pull itself in O.D.

[Willyum]

I forgot to mention that you should get as much info as possible about what kind of problems you might have changing the coupling at the transmission to bell housing. I never suspected what I was getting into. I had to take the oil pan off the engine and pull the rear main cap to change the bolts holding the flywheel, they were a different length on the automatic. I have since heard from some that they actually had to pull the engine and change the crankshaft. Additionally rigging up the clutch assembly and interior cosmetics was difficult even considering I was pulling my parts of an exact same model donor car.

[daddyo8]

Thanks Willyum, I'll do some more research, and maybe look for a matching rear end.Luckily I'm not changing the tranny, just the rear end.