Differential Swap Help - E30 Beginner

[bdwE30]

Greeting,

After 8 months of searching, I finally entered the E30 cult with a 1984 325E purchase. My E30 has a M50 swap and 5-speed.

The car runs fantastic, but I am interested in a differential swap. Currently it has a 2.79 gear ratio in a medium case.

I would like to swap to a much higher gear ratio. I use it as a daily driver and don't often go over 60 MPH (never go over 85 MPH) but enjoy the acxelation getting there.

I've been shopping around for a new differential and am overwhelmed at the options and my general lack of knowledge. I would hate to spend $700 on the swap and have it be less than ideal.

Any help would be greatly appreciated. My current questions revolve around limited slip or open, can any e30 differential fit, transition between medium and small case.

Thanks much for your time and consideration.

[5Toes]

limited slip from an e28 535is or 535i with the LSD option. its a 3.25 ratio. just drop out your old diff and remove the rear cover, bolt the rear cover up to the new e28 diff. Then use a large screwdriver and pop out the output flanges and swap those to the enw diff too and install. Use redline LSD rated fluid and have fun.

[Fsnow]

If you are going through the trouble of sourcing and installing a diff make sure you get a lsd. Any e30 diff will fit but stay away from small case since you have an m50. As for a ratio that seems to be a matter of personal preference depending on driving style and economy . I'm sure someone with an m50 or similar swap will have a suggestion for you.

[5Toes]

oops missed the m50 swap part. A 3.73 LSD from a 325is e30 should fit the bill then and turn ncie revs on the highway.

[bdwE30]

Thanks all. Based on your input it won't matter in the swap if the case is small or medium (medium preferred)?

[bdwE30]

Does it matter if the differential is pulled from an automatic or manual?

[5Toes]

a small case on an m50 swap is a bad diea. they only put small cases in 4 cylinder cars for a reason (with the exception of the e30 m3)

no auto or manual doesnt matter. auto i is a medium case 4.10, manual 325i is a medium case 3.73

[bdwE30]

Thanks again. I think I am ready to pull the trigger on a purchase. When making the swap, is there anything else that is a must to replaceshould when it is torn apart? Differential mount? Output gaskets?

[stonea]

I would go a head and do the Diff bushing and Diff cover gasket at minimum.

[crappycoco]

I'd go for the 188mm 3.73 LSD out of the 325is.
Change the bushing(do NOT buy the $20 bushings), cover gasket - I'd recommend the dog-ears and clutch disks too (I got mine from thayer), and if you're in there you can change the axle seals.

I would also recommend to check the diff for play before you buy it (grab the yoke and turn it to each side. A noticeable clunk is a bad sigh). A lot of them are beat up. I bought a "new" used one because my old one's bearings were getting loud, only to find out the new one had the same problem =)

[b-rad]

Any opinions on diff cover swap? I have S50 with 3.73 LSD.
shop is suggesting cover swap, explain... more fins basically?
Also this looks interesting also LINK

S50 is powerful but not sure I need?
Will be changing out the poly with Garagistic as well, the kit.

[stonea]

I don't think the fins are necessary. IMO the shop is probably just trying to get more money out of you. Theres people on here running a lot more than S50 numbers and are just fine. The second ear is cool, but I don't know why garagistic machined a second ear tab when you can just use a e36 cover.

[jeffnhiscars]

I'd change the output flange gaskets and O rings. Quick and easy w the diff out

[crappycoco]

The fancy diff cover would help getting rid of excess heat, but I don't think you track the car for extended periods of time for that to be a problem. The medium case can handle three M50's on stock internals, so you should be good =)