Author Topic: Differential, Small case vs Medium? (Read 7732 times)

TG197 · « **on:** August 21, 2011, 11:30:52 AM »

I need to replace my Differential (small case, 4.10 open), will a medium case
(188mm) bolt right in ?. It is hard to find the small case w/ 4.10. The reason I am looking to replace the unit is that the component that the ring gear is attached to (spool?) has broken in half. However, I have disassmbled the Diff. and it would be just as well to replace the broken part if I could find one.

romkasponka · « **Reply #1 on:** August 21, 2011, 12:59:47 PM »

Quote from: TG197;106259

I need to replace my Differential (small case, 4.10 open), will a medium case
(188mm) bolt right in ?. It is hard to find the small case w/ 4.10. The reason I am looking to replace the unit is that the component that the ring gear is attached to (spool?) has broken in half. However, I have disassmbled the Diff. and it would be just as well to replace the broken part if I could find one.

Yes, it's bolt right in. Could be that you will need driveshaft lenght adjustment in the middle.

TG197 · « **Reply #2 on:** August 21, 2011, 01:10:15 PM »

Thanks, that is good news, as there is a lot more medium case diff.'s for sale
than the small case. I want to stay with the 4.10 ratio.

Balkanac · « **Reply #3 on:** August 22, 2011, 03:51:24 AM »

I have a medium case 4.10 LSD off a US model e30 m3 and it bolted right in. Didnt need to touch the driveshaft. Apparently small case diffs are prone to beakage, where mediums can take a lot more

DesktopDave · « **Reply #4 on:** August 22, 2011, 07:25:11 AM »

Same here. My small case 4.10 died and I replaced it with a 3.73 LSD from an '87 325is. Bolted right in. Like romasponka said, I had to adjust the drive shaft length slightly.

This is a good time to replace the center support bearing and guibo as well...

91 e30m42 · « **Reply #5 on:** September 13, 2011, 06:34:06 PM »

now how do you adjust the drive shaft length slightly as im kinda interested in this mod as well.... sorry for the thread jack

romkasponka · « **Reply #6 on:** September 14, 2011, 02:24:18 PM »

Quote from: 91 e30m42;106659

now how do you adjust the drive shaft length slightly as im kinda interested in this mod as well.... sorry for the thread jack

In the middle you have big nut...

DesktopDave · « **Reply #7 on:** September 14, 2011, 09:03:15 PM »

+1...there is a really large nut in the middle of the driveshaft. It looks like a sleeve but the sheet metal is flanged out in a hex shape. The shaft is two pieces splined together under that cap with a rubber sleeve.

Also check your tranny mounts, guibo, center support bearing and rear u-joint while you're under there.

I wire brush the splines & spray some PB Blaster to clean them out. You can compensate an easy 2-3" for longer diffs. If you do replace the center support bearing while you're there, it comes off the spline joint after removing a big circlip. Be sure you pre-load the CSB forward 4-6mm when you put it back together.

91 e30m42 · « **Reply #8 on:** September 14, 2011, 10:51:02 PM »

great dtails there dave thank you will be looking more into this...as for all my mounts and bushings they are all new so no worries in there

mtle30 · « **Reply #9 on:** February 16, 2012, 05:47:09 PM »

I'm having this differential issue, I was lucky to get a free refurbished driveshaft from a 325, however the problem I'm having is the center Lange that bolts up to the car doesn't match with the car, and I have a 4.10 LSD medium case. The size of the driveshaft with diff is good but I can't bolt up the driveshaft, anyone have suggestions?

How exactly would I shorten my current driveshaft to fit the 4.10 LSD medium case?