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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > Decided to fit a M3 diff



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      01-17-2013, 06:06 PM   #243
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Quote:
Originally Posted by N111CUK View Post
Hi, I have an auto and also have found an M3 DCT complete subframe.

My question is, does this final drive (3,15) work better for you. I also have a heavily modded car pushing over 400WHP so this will help determine the final drive
I have the M3 rear on my FBO 135i and I am also 6AT. Going taller than stock sounds silly to me. I have the 3.85 of the manual M3 and it is perfect.
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      01-17-2013, 06:46 PM   #244
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I just figured that with my setup launching from 2nd gear is better because i have the torque exchange in my transmission

therefore going taller would mean 1st gear is more usable for standing starts. once rolling 6AT's just adjust accordingly and wit all the torque of the N54 those taller gears would suit it better.

what do you think?
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      01-18-2013, 03:27 AM   #245
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Quote:
Originally Posted by N111CUK View Post
I just figured that with my setup launching from 2nd gear is better because i have the torque exchange in my transmission

therefore going taller would mean 1st gear is more usable for standing starts. once rolling 6AT's just adjust accordingly and wit all the torque of the N54 those taller gears would suit it better.

what do you think?
I would say keep as close as possible to OEM even going a bit shorter is good.

Remember it is not just for the launch...
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      01-18-2013, 06:44 AM   #246
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Originally Posted by RimasRS View Post
I would say keep as close as possible to OEM even going a bit shorter is good.

Remember it is not just for the launch...
George mentions there are final drive options for this diff.

So I can presume that apart from the final drive gearing there is no difference between the DCT and MT diffs

Maybe I need to learn how difficult is it to change final drive gears in the diff.
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      01-18-2013, 07:38 AM   #247
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Quote:
Originally Posted by N111CUK View Post
I just figured that with my setup launching from 2nd gear is better because i have the torque exchange in my transmission

therefore going taller would mean 1st gear is more usable for standing starts. once rolling 6AT's just adjust accordingly and wit all the torque of the N54 those taller gears would suit it better.

what do you think?
I have the 3.15 with auto. 1st gear is perfect as its a bit shorter than my stock 2nd gear for launches but not short enough to make the launch very tricky.
The only major negative I have is that at highway speeds the revs in 6th sit in the drone sweet spot of the AE Exhaust I had on. It was unbearable and I have put stock exhaust back on. At 120-130km/h the car cruising right in the droning spot.
My consumption with the diff also sits lower than 10L/100km always.
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      01-18-2013, 08:55 AM   #248
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Quote:
Originally Posted by GeorgeSmooth View Post
I have the 3.15 with auto. 1st gear is perfect as its a bit shorter than my stock 2nd gear for launches but not short enough to make the launch very tricky.
The only major negative I have is that at highway speeds the revs in 6th sit in the drone sweet spot of the AE Exhaust I had on. It was unbearable and I have put stock exhaust back on. At 120-130km/h the car cruising right in the droning spot.
My consumption with the diff also sits lower than 10L/100km always.
Thanks for the heads up. I'm also thinking the 3.15 would make more sense because we have all that torque to play with.

Is the M3 Manual diff shorter FD than our OEM diff? if it is then the dct is the best choice
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      01-18-2013, 11:40 AM   #249
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Hey George, didn't realise you were an auto 335i. Does that mean you went from 3.46 stock to 3.15? I'm kinda planning on going shorter rather than longer.
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      01-18-2013, 11:40 AM   #250
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      01-19-2013, 02:17 AM   #251
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Quote:
Originally Posted by Nigelo View Post
Hey George, didn't realise you were an auto 335i. Does that mean you went from 3.46 stock to 3.15? I'm kinda planning on going shorter rather than longer.
I went with the 3.85 M3 manual diff first which was a bit short for my liking then fitted the DCT 3.15. I have RB's and am always at the 440whp level so the longer 2nd allows for slightly better traction on road. With the 3.85 I would loose traction at the lower end of third with stock Michelin RFT.
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      01-19-2013, 03:26 AM   #252
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Quote:
Originally Posted by N111CUK View Post
George mentions there are final drive options for this diff.

So I can presume that apart from the final drive gearing there is no difference between the DCT and MT diffs

Maybe I need to learn how difficult is it to change final drive gears in the diff.
From my head I think even the finned cover of diff has different part numbers so I'm not sure about are internals same. Though still I don't know what is your car MT DCT or AT but like I said for best performance stay close to OEM ratio.
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      01-19-2013, 04:05 AM   #253
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Quote:
Originally Posted by N111CUK View Post
Thanks for the heads up. I'm also thinking the 3.15 would make more sense because we have all that torque to play with.

Is the M3 Manual diff shorter FD than our OEM diff? if it is then the dct is the best choice
The Manual diff is 3.85 .
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      01-19-2013, 09:48 AM   #254
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Quote:
Originally Posted by GeorgeSmooth View Post
The Manual diff is 3.85 .
So the 335i 6AT OEM diff is 3.46 FD

M3 Diffs
M3 dct is 3.15 FD
M3 mt is 3.85 FD

So in fact they are both +/- 0.30 FD difference

Based on the fact I'm running more power going longer must be the better option

As for the 335i MT diff it's 3.08 FD therefore the M3 DCT diff is the clear choice because the M3 manual 3.85 FD thats going to shorten the gearing significantly. Imagine that with slick drag rear wheels
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      02-10-2013, 11:41 PM   #255
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George, were the 3.15 and 3.85 diffs different lengths? Did you have to modify the driveshaft again when you switched?

On my 6 mt the front half of the m3 shaft ended up being 673 mm from center bearing to guibo face. Put a couple hundred miles on it so far. Theres a slighy wobble but we're trying again. I'm actually wondering because the m3 manual shaft on realoem is only a couple mm from my final driveshaft length. Not that it matters because they had to re-tube it to switch the tri-flange, but just wondering if I'd have bought the m3 manual shaft if this would've been easier...
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      02-11-2013, 05:03 AM   #256
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Hey Skyguy, nice work. If you don't mind I'm going to use your measurements to get my Mt driveshaft made up.

Are you happy with the length, or would you change it at all? Is the guibo the rubber end piece that bolts on to the driveshaft? And was there a particular part of the centre bearing you measured from? :-)

Thanks!
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      02-11-2013, 05:03 AM   #257
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      02-11-2013, 09:23 AM   #258
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Guibo or flex-disk, yeah same thing. If you're looking underneath at the two sets of center bearing mounting holes, they measured from the center-point of the rear set of holes to the face where the flex-disk bushings meet the tri-flange on the shaft. Like I said I'm still having some wobble accelerating through 20-25mph, I'll update when they tell me it's fixed and what the solution was. Hopefully it's not a length issue, so to speak...
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      02-11-2013, 09:53 AM   #259
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I had the wobble at 25mph full throttle

this is because you have to use the 335i center shaft bearing on the M3 one.

The M3 bearing will not align the shaft to the gearbox, it will hang the shaft too low!!!!
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      02-11-2013, 09:55 AM   #260
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Quote:
Originally Posted by skyguy View Post
George, were the 3.15 and 3.85 diffs different lengths? Did you have to modify the driveshaft again when you switched?

On my 6 mt the front half of the m3 shaft ended up being 673 mm from center bearing to guibo face. Put a couple hundred miles on it so far. Theres a slighy wobble but we're trying again. I'm actually wondering because the m3 manual shaft on realoem is only a couple mm from my final driveshaft length. Not that it matters because they had to re-tube it to switch the tri-flange, but just wondering if I'd have bought the m3 manual shaft if this would've been easier...
Yes the manual is about 15mm longer, you don't have to retube, simply cut the old flange and weld the new one... I did mine at 677mm
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      02-11-2013, 11:18 AM   #261
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Can the M3 centre bearing be swapped for a 335i one?
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      02-11-2013, 11:32 AM   #262
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Quote:
Originally Posted by marconi118 View Post
Yes the manual is about 15mm longer, you don't have to retube, simply cut the old flange and weld the new one... I did mine at 677mm
I see the shaft difference is 15mm but is that all at the diff end, or all at the trans end, was the question? I do see where you said that about the center bearing many pages back but guess I didn't pay close enough attention and now don't have my center bearing... I'll have to call about getting it back.

Must me a very slight difference I didn't even notice it, hope that will solve my problem.

Thanks,
Sky
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      02-11-2013, 11:39 AM   #263
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I had to refit the shaft 3 times and ask an expert friend to notice this difference, you simply can't see it below the car.
It was a nightmare to find out!!!!!!!!!!!!

If I remember well it is 10mm difference, because the M3 gearbox sits lower, it is a V8... you can reuse the one of the 335i it fits the M3 mid shaft.

My 677mm are from the middle of the hole in the bearing (where it bolts to the car) to the flange surface where it meets the guybo at the gearbox
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      02-11-2013, 11:47 AM   #264
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Thanks so much for the response Marconi. Really hoping it's really this easy of a fix, never had the center bearings next to each other separated from the shafts but now the difference looks obvious. Crossing my fingers they still have my bearing and don't charge me.



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