750i Differential gear question

[grave77]

I was looking for the stock manual tranny differential gear which was 3.25 I think. I asked about the 750i and I found it was 3.15 would it fit on my 535i or the input flange is different? I'm not looking for a powerfull take off just smooth high way running is fine for the time being ... I also think that the manual tranny will overcome the low ratio. ... please any advice? thanks

[bfd]

I was looking for the stock manual tranny differential gear which was 3.25 I think. I asked about the 750i and I found it was 3.15 would it fit on my 535i or the input flange is different? I'm not looking for a powerfull take off just smooth high way running is fine for the time being ... I also think that the manual tranny will overcome the low ratio. ... please any advice? thanks

What's wrong with your stock differential? You do know the stock gearing for a manual 535i is 3.46. Going to a 3.15 is definitely gonna make you slower, even with a stick. Although if all you're doing is highway cruising, you should be able to get better mileage. STill, these cars are heavy, so you mileage ain't gonna improve that much. If you want better mileage, GET A HONDA....

[632 Regal]

Barry,
I went from 3:15 to 3:64 and NO adverse mileage...much more drivable. You should try to see how it acts with the manual before guessing gear ratios anyways.

[grave77]

nothing wrong, but I have converted my auto tranny to manual and then my car turned very heavy and slow, max speed @ 6200 RPM is 210Km/h I'm looking for 255Km/h max speed or 260. I was told that 3.25 diff. is the stock ratio for the manual. and it seems that the German specs are different since they have the Autoban highways .. I need the right one now... I just guessed that the 3.15 will work fine ... by the way I can take off on the second speed now and the 3rd speed feels like the second speed.

[632 Regal]

find out what gear your car "actually" has...no guessing here, there should be a tag on the back of the differential cover.

[grave77]

its 3.91 now ... workes fine if I had 6 speeds but on 5 it sux!!

[632 Regal]

ahhh! 3:91 now we are starting to get somewhere...now you need to find out the final drive ratios on both transmissions and do the math accordingly.

[JonE]

Probably going to want that 3.46 diff. or some have liked the slightly higher 3.64?

[grave77]

see ... well ... is there a factor that comes in between? do u have that equation I need to calculate? ... is there a list with the BMWs that has the same ratio so I can look it up ... I'm facing a lot of shi** with those guys at the junkyard ... they dunno shi* about this ... I need a point to start from .. 750, 740, 540 has 3.15 right 535 has 3.91, 3.64 and 3.46? how about the 525?

[632 Regal]

as far as I know in US cars the rear deffs in the 540s and //M series cars have a larger ubit, dont know how easy they can be retrifitted. The diffs in the 20s 30s and 535s should all be a direct bolt in, however watch the flanges, those might need to be swapped even though the books say they are a direct bolt in. If you figure what gear ration you need heed this warning, watch carefully as the flanges are swapped... see here. If not done correctly you WILL have this problem.
http://www.bimmer.info/~regal632/rearend.html