Author Topic: Diff swap (Read 11113 times)

91318isguy · « **on:** July 06, 2007, 12:16:47 PM »

Hi all,

I've been looking through the forum and I can't find the specific subject I'm looking for.

I'm wanting to eventually do a Diff swap from my 4.1 to a limited slip. Have any of you other wrench heads ever done this? Is the 325 the most prolific for the E30? Seems like all the swaps I see is from a 318is 4.10 to the 325. A buddy of mine was looking at the 91 325 is and mentioned that stock the 325 has 30 more ponies. I know alot of people have done stuff like this but (please forgive this... I do love the M42), what is it that makes the M42 better than the 325?

91318isguy
FOREVERM42

dino245 · « **Reply #1 on:** July 06, 2007, 01:11:26 PM »

The E30 318is came with a small case 4.10 diff but there are a few out there with a 4.10 LSD in a small case. The small case diff also came in a 3.91 lsd in the early 318i with the M10 4 cyl. engine.

Now the 6 cyl E30's came with a medium size diff in many different ratios. This diff also came on the E30 M3.

In the early days of my mods I decided to get the small case 3.91 lsd diff. Now that I am aiming for more power so I will be looking for a 3.91 medium case lsd diff. The small case diffs cant handle too much power and there is only one clutch disc in the LSD as oposed to 2 in the medium diffs which equals more surface area.

91318isguy · « **Reply #2 on:** July 06, 2007, 01:23:42 PM »

Thanks.

How hard is the swap? What should I be expecting to spend? If I do the swap, I may-as-well do the medium case diff with the 2 disks. That's and LSD right?

Vladi · « **Reply #3 on:** July 06, 2007, 05:30:38 PM »

Quote from: dino245;29174

The small case diffs cant handle too much power and there is only one clutch disc in the LSD as oposed to 2 in the medium diffs which equals more surface area.

So how does that translate in performance? Why exactly is the medium case lsd better than the small ones?

silverblades181 · « **Reply #4 on:** July 06, 2007, 05:46:28 PM »

If you swap a 4.10 small case LSD it's pretty easy. Just swap diff should take about 2-3 hours on jack stands. If your putting a medium case you'll need to use the drive axles from a 325.

The medium case isnt better then the small case, it can handle more power that's all. With a stock M42, the small case is plenty.

AL GReeNeRy · « **Reply #5 on:** July 07, 2007, 02:56:32 AM »

Quote from: silverblades181;29187

If you swap a 4.10 small case LSD it's pretty easy. Just swap diff should take about 2-3 hours on jack stands. If your putting a medium case you'll need to use the drive axles from a 325.

The medium case isnt better then the small case, it can handle more power that's all. With a stock M42, the small case is plenty.

i just did the swap from a 4.10 open small case to a 4.10 LSD medium case out of an m3. it was a straight swap. didnt have to replace anything but the differential. no problems so far. had it in for about a week and its taken some abuse so far with no problems and that includes a whole day of writing my name in the streeeetttsss.

twinpop171 · « **Reply #6 on:** July 07, 2007, 09:18:11 AM »

I'm going to do a diff. swap as well. My m42 has an open 3.73 in it and my '89 325i DD has a 4.10 LSD in it. I want to do the swap but want to make sure that it IS a direct swap.

How can you tell the difference between a small and medium case differential? I've done searches on this before but I have never really found out the answer.

The PO must have changed it at some point. Something that is a odd on my m42 is that the passenger side rear wheel is a little bit more outboard than the drivers side rear wheel. The car drives as straight as can be. Is it possible that it could have 2 different size half shafts from the previous swap? I' ve owned the car for over 2 years and have never been able to figure this out and never addressed this in the forums. Has anyone ever seen this?:confused:

Thanks, Dan.

gearheadE30 · « **Reply #7 on:** July 07, 2007, 08:35:06 PM »

The half shaft length wouldn't alter the track of the car. The hubs would have to be different to do that. Chack and make sure that the car doesn't have spacers in one wheel. Another common thing is for people to put wheels on from a 325ix, which has a different offset.

I recently had my pumpkin out to put in a poly bushing from AKG motorsports. It is fairly easy to do, but many of the bolts are in difficult to reach areas and are covered in about an inch of road grime...

BrandC · « **Reply #8 on:** July 08, 2007, 07:51:49 AM »

Quote from: twinpop171;29203

I'm going to do a diff. swap as well. My m42 has an open 3.73 in it and my '89 325i DD has a 4.10 LSD in it.

Your car must be slow as piss with that 3.73 diff. with your M42. That is way too tall for the little torque it already generates. Definitely swap over that 4.10 LSD unit from your 325i.

scorptrigger · « **Reply #9 on:** July 08, 2007, 02:47:20 PM »

I just got a 91 e30 318is with 44,000 miles on it. I would like to know if there isany problem with swapping to a 4.44 LSD from a e36 318ti? I have not seen any mention of this but it seems like the best option to me.

silverblades181 · « **Reply #10 on:** July 08, 2007, 05:15:14 PM »

it will work, 1st gear will be short as hell but you'll have a lot more torque. My friend has an E30 M3 and he swapped his diff for a 4.27 LSD and he says the engine revs higher but doesn't have to work as hard to get the car moving, he loves it. I imagine a 4.44 is a bit radical for street use but it is something I'd like. The powerband on the M42 is so high, you'll reach it faster.

BrandC · « **Reply #11 on:** July 08, 2007, 09:22:13 PM »

Quote from: scorptrigger;29247

I just got a 91 e30 318is with 44,000 miles on it. I would like to know if there isany problem with swapping to a 4.44 LSD from a e36 318ti? I have not seen any mention of this but it seems like the best option to me.

Problem: It won't fit. E36 diffs do not work on E30 subframes. I believe the only diff cover that does it the M-Coupe finned cover.

twinpop171 · « **Reply #12 on:** July 08, 2007, 09:51:35 PM »

Quote from: BrandC;29236

Your car must be slow as piss with that 3.73 diff. with your M42. That is way too tall for the little torque it already generates. Definitely swap over that 4.10 LSD unit from your 325i.

I don't think it is slow as piss but then I don't have any other m42s around here to compare with.

I'll definitely post a thread after the swap. I'm very curious to see the change in torque.

Wise Old Dog · « **Reply #13 on:** July 08, 2007, 10:06:42 PM »

If I'm not mistaken, the Ti is the only e36 that uses the diff layout from the e30. I read that somewhere.

AL GReeNeRy · « **Reply #14 on:** July 09, 2007, 03:43:07 AM »

Quote from: Wise Old Dog;29262

If I'm not mistaken, the Ti is the only e36 that uses the diff layout from the e30. I read that somewhere.

the 318ti is the only e36 that closely resembles an e30 suspension-wise. actually, you can use parts off a 318ti to do a "poor mans" 5 lug swap. not quite sure about the differential, but i wouldnt doubt it one bit