e36 LSD unit swap

JamesShort · **Posted:** Tue May 25, 2010 10:28 am

I think Keith/Mike/Chuck rang in on this in another thread but in researching my potential project car, I want to gather some info on this job.

So I think I'll be looking to build an STX legal 96-00 328 for autox/track. So from what I'm seeing, finding one with LSD is almost impossible, so an M3/325 LSD unit (as Keith put it, the 'chunk'

) swap might be in order, but I have to keep the stock R/P ratio from the 328.

I'm looking around the intraweb and I haven't really seen a good BMW diff rebuild or LSD unit swap (only swaps are full diffs which I can't do). My brother in laws Bentley manual is no help in this regard.

To put my ability in perspective, I took apart and rebuilt a d-series honda 5spd to replace an IS bearing....wasn't a cake walk but I got it done and it works, so a diff rebuild doesn't scare me much.

It seems to me, I'd yank the output flanges out of the diff. Unbolt the 'plates' on the sides of the diff (which I assume hold the output flange bearing races), open the back cover and the whole ring gear/lsd unit is free to be removed. Unbolt the ring gear from the open diff (think it's pressed on as well as bolted on), press ring gear on LSD unit from 325/M3, bolt 'er up, drop unit back in (check bearings while I'm in there), put the output flange bearing races back on and bolt to diff case, insert output flanges, done.

If anyone has experience with this, or more BMW specific info/forum threads etc, it'd be appreciated.

JamesShort · **Posted:** Tue May 25, 2010 10:42 am

Score! :

http://forums.bimmerforums.com/forum/sh ... p?t=894366

Since I'll be keeping the 328 case and R/P, I won't have to worrying about gear backlash or bearing preloads. This assumes the output bearings are in good shape.

EDIT: Actually I think I got ahead of myself. The open diff and LSD output carriers are not the same

. The question is, can I take them off the donor diff and put them in the 328 diff. My plan is to just buy a whole diff for an M3 or 325 so I will have the output carriers from the LSD base diff. I'll also have to use the shims from the LSD case on the 328 case (and on the right side!). This assumes, again, that the output carriers from the LSD case fit the open case.

And I'll have to remove the output bearing on the side with the speed sensor ring so I can get the ring gear off

. Someone said you can slightly bend the speed sensor wheel a bit to get the ring gear off....I guess that's a last ditch option if I don't feel like having to press off and press on a new bearing.

MarcusMcRae · **Posted:** Tue May 25, 2010 5:41 pm

Shoot diffsonlne.com an email. They were always very helpful with any qustions. You could also speak to Mark Cooper @ performance chassis. I know he has done several diff swaps and rebuilds.

steve remchak · **Posted:** Tue May 25, 2010 6:26 pm

mine came from VAC. send them a core and they send you a diff. i would suggest the finned diff cover also as it helps in cooling and holds more fluid.

whether any of this is AutoX legal i can't say as i don't AutoX. i have an aversion for cones. :twisted:

http://www.vacmotorsports.com/

BTW the 3.64 is a perfect fit once you do the OBD I intake swap & cams. i went with used S50 cams. with 17" wheels the powerband comes in nicely.

JamesShort · **Posted:** Tue May 25, 2010 7:07 pm

Geeze Steve, you keep taunting me with all of these fun mods....maybe I should just ditch this STX build

.

Sean O'Connell · **Posted:** Tue May 25, 2010 7:32 pm

have you bought the car yet? why are you not considering a older 325?

steve remchak · **Posted:** Tue May 25, 2010 7:57 pm

JamesShort wrote:

Geeze Steve, you keep taunting me with all of these fun mods....maybe I should just ditch this STX build

.

do ya think?

mine puts a measly 209 to the wheels James. i have heard 240 RWHP is possible.

but as Sean is suggesting, the 328 2.8 might limit you. ideally an OBDI car is better to build on.

JamesShort · **Posted:** Tue May 25, 2010 8:20 pm

Sean O'Connell wrote:

have you bought the car yet? why are you not considering a older 325?

Nope. Steve and Keith had me convinced I should get the 328 for the better power band etc but the diff became the issue to have LSD and the stock R/P ratio.

Then off course Steve has taunted with me with an m50 intake manifold, OBD1 conversion, and low geared lsd onto a 328 which throws my STX hopes out the door

.

But if I go 325, getting stock LSD will be much easier. How much power do you think a 325 puts to the ground after intake, exhaust, tune (timing, fuel etc)? Is there any major suspension difference between the 325 and 328?

Sean O'Connell · **Posted:** Tue May 25, 2010 9:04 pm

what i was hinting at is a 92-95 325 has endless possibilities of where to end up. all suspension parts on all e36 including the M3 are swappable same goes for motors and well anything. the 325 being obd1 will let you go to an s52 with an obd1 conversion putting down more power than you could ever get out of an 2.8 without spending your lifes savings. being older will mean its cheaper and you'll have more of a budget for the go fast parts. the 2.5 should be able to keep up with Steve's 2.8 if done correctly.

Richard Casto · **Posted:** Tue May 25, 2010 9:10 pm

James,

I don't have any BMW transmission/diff experience, but I can say on a Porsche, that if you swap out the diff, using the same ring gear, shims, bearings, etc. is not a guarantee that the bearing pre-load and backlash will be the same. This is because the dimensions on the LSD may be slightly different than the open diff.

If it was me, I would get familiar with the process for setting bearing preload and backlash. You might get lucky and use the existing shims and it all might work out just fine. But I would measure once assembled just to make sure.

Richard

JamesShort · **Posted:** Tue May 25, 2010 9:11 pm

Sean O'Connell wrote:

what i was hinting at is a 92-95 325 has endless possibilities of where to end up. all suspension parts on all e36 including the M3 are swappable same goes for motors and well anything. the 325 being obd1 will let you go to an s52 with an obd1 conversion putting down more power than you could ever get out of an 2.8 without spending your lifes savings. being older will mean its cheaper and you'll have more of a budget for the go fast parts. the 2.5 should be able to keep up with Steve's 2.8 if done correctly.

I like where you are going. If I build to STX specs.....and I turn out to like tracking it more than autoxing it, I have a lot more room to upgrade (and money to do so)

with the 325.

JamesShort · **Posted:** Tue May 25, 2010 9:14 pm

Richard Casto wrote:

James,

I don't have any BMW transmission/diff experience, but I can say on a Porsche, that if you swap out the diff, using the same ring gear, shims, bearings, etc. is not a guarantee that the bearing pre-load and backlash will be the same. This is because the dimensions on the LSD may be slightly different than the open diff.

If it was me, I would get familiar with the process for setting bearing preload and backlash. You might get lucky and use the existing shims and it all might work out just fine. But I would measure once assembled just to make sure.

Richard

Thanks for the info. I've been emailing Dan at diffsonline and he might have a setup for me and that's basically what he is saying but he said with the LSD carrier unit he'd sell me, the backlash and bearing preload would be pretty easy to setup.

But as you can see with Sean's suggestions....I might not need to do this afterall

.

JamesShort · **Posted:** Wed May 26, 2010 10:47 pm

What mileage should I start getting wary about an M50? My father in laws 95 325is auto has like 250k and is going strong-ish. Also finding a 325is in sedan form (5spd) is proving to be much more difficult than in coupe form (5spd). I guess I can get a 325i and do the LSD swap as a whole diff unit and since I'm going to do suspension I don't care about the sport suspension...don't care about the spoiler or onboard computer either.

MarcusMcRae · **Posted:** Wed May 26, 2010 11:27 pm

Why do you want a sedan?

Try to shoot for less than 150k. If properly maintained they can still run strong till 250k pretty easily.

steve remchak · **Posted:** Thu May 27, 2010 7:58 am

MarcusMcRae wrote:

Why do you want a sedan?

Try to shoot for less than 150k. If properly maintained they can still run strong till 250k pretty easily.

structurally the sedans are stronger. but i'm sure it is a minimal difference.

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