School me on diff rebuilds

[Earendil]

It's winter again, and winter means it's time to rebuild my 4.10 diff. I had originally bought the diff with the understanding it was a good diff, well it's LSD functionality is good to about 10ft/lb and then it breaks loose, so the discs are shot... I think.

Here is my understanding, and I'd like someone in the know to confirm or school me.

• Rebuilding an E30 diff is "easy", as long as no bearings are replaced.
• Bad Bearings will cause a whine.
• Bad bearings won't effect lockup.
• An LSD that acts like an open needs to have the clutches replaced.
• Replacing clutches and dog ears in a medium case LSD diffs is not difficult if the person is halfway competent.
• If the Diff is quite, there is no need to mess with the bearings.

Are those statements all correct?

Additional question:
I believe I understand what kills the clutches, but what kills bearings?

I hope to follow this guide by Yoshi when the time comes, but I don't want to crack open a diff without knowing exactly what I'm in for first!

Thanks!

[SkiFree]

Write-up for the small case.

http://www.bmw2002faq.com/component/...opic/t,379621/

Same general theory as Yoshi. I don't see how you could have a "rebuilt diff" if you don't put in new bearings/races.

[FredK]

If the bearings are quiet, I would just replace the clutch discs.

Bearings go bad due to normal wear. This happens extremely slowly under normal circumstances. Wear can be accelerated by contaminants in the oil (particulate contamination--friction disc material + steels), or insufficient lubrication properties due to oil breakdown, or because of insufficient lubrication properties due to operation out of the temperature limits of the oil (common for track cars).

[Earendil]

Write-up for the small case.

http://www.bmw2002faq.com/component/...opic/t,379621/

Same general theory as Yoshi. I don't see how you could have a "rebuilt diff" if you don't put in new bearings/races.

That's why I say "Rebuilding an E30 diff is "easy", as long as no bearings are replaced". It's a limited rebuild, as it'll just be the clutches, dog ears, seals, bolts, and anything else that is easy and cheap to do at the same time. Anything that brings it back up to factory spec and prevents it from leaking oil in the future. Call that what you want :)

[jlevie]

With the exception of the second item in the list above, the rest are true. Bad bearings can cause noise, either from the bearings or from incorrect pinion to ring gear engagement.

[demlotcrew]

That's why I say "Rebuilding an E30 diff is "easy", as long as no bearings are replaced". It's a limited rebuild, as it'll just be the clutches, dog ears, seals, bolts, and anything else that is easy and cheap to do at the same time. Anything that brings it back up to factory spec and prevents it from leaking oil in the future. Call that what you want :)

If rebuilding a stock LSD with two clutches, you can rotate the dog plates, saving you money.

Andrew