Diff mix up

[smonkbmw]

i have a 89 325i.

i bought a 3.91lsd diff from a 84 318. ive been told its not going to fit? something about the drive shafts being to short because the 318 is a small case diff and the stock 3.73 is a medium case?

what do i need to get the 3.91 to fit? i heard all that i need is the driveshafts? help!

[MikeE30325i]

i believe it would be a longer driveshaft, or pay a shop to extend your slightly.

[smonkbmw]

the driveline from the trans to the diff? or the shafts from the diff to the wheels?

[MikeE30325i]

maybe all of them. depends on how less wide the diff is

[Mr Deagle]

it will bolt right up, dont worry

edit: dont do burnouts or you will blow the small case diff up

[tophertii]

I own a 318is, small case 4:10. I just bought a med case 4:10 lsd out of a 91 vert auto. No fit! If you mesure from the end of the diff flange to the center of the upper mounting holes there is about a 1/2" difference. Damn I need a new diff!

[Mr Deagle]

uh oh, looks like im keeping the subframe from my parts car........for my 318i (84)

[trent]

uh oh, looks like im keeping the subframe from my parts car........for my 318i (84)

No, you are correct. A large case 4.10 bolted directly into my 84 318 subframe.

[trent]

I own a 318is, small case 4:10. I just bought a med case 4:10 lsd out of a 91 vert auto. No fit! If you mesure from the end of the diff flange to the center of the upper mounting holes there is about a 1/2" difference. Damn I need a new diff!

You have a different problem. This should fit perfect.

[tophertii]

I'm going to document this with pics and post it. I spent literally hours researching wether a med case would fit or not, this site and others. I purchased the diff only after I felt certain that it would fit.

I tried installing it three times and couldn't line up the diff holes with the sub frame. I finally decided to reinstall the stock small case. Bolted up in minutes with no such problems. I later found posts from people with the same problem. It is like the drive shaft is too long.

I would love to find out that the I made a mistake at installing it. I bought the diff and a salvage yard and they do not offer refunds. I also dumped in 25 bucks of Redline fluid.

Someone enlighten me and tell me what mistake I may have made installing it.

[trent]

Are the input flanges different? I would love to see pix.

[crunk3]

I own a 318is, small case 4:10. I just bought a med case 4:10 lsd out of a 91 vert auto. No fit! If you mesure from the end of the diff flange to the center of the upper mounting holes there is about a 1/2" difference. Damn I need a new diff!

Il buy your diff off u if your gonna sell it :D

[tophertii]

I'm not sure were the added length comes from, the flanges seem the same. It is hard to find consistent reference points to measure. I think if I place something like a large flat piece of wood on the end of the diff flange and measure straight back to the mounting holes I can take pics and show the difference.

I was pulling my hair out at 1:30 am the other night I quickly tried this with a piece of 2"x 10". I hope to try this again with a better piece of wood or something more suitable.

As I said I would love to be wrong. I will try to get some pics up in the next couple of days or at the latest by the weekend.

[Rocla]

Someone enlighten me and tell me what mistake I may have made installing it.

Ever wondered why there is a sliding joint on drive shaft?

All e30 diffs do interchange, if you replace typ168(small case) with typ188(med, e30 "big") or vice versa you must adjust drive shaft lenght, because the pinioin "nose" is different in lenght.

Typ210 diff however will not bolt to e30 subframe.

[tophertii]

Thanks, for the info. Seems obvious now that you mention it. This is the first time I have found this info and as I have learned I'm not the only one that has faced this problem. If by chance you ever make it to SLC Utah the beer is on me. I may have an LSD yet!