Changing diff ratio questions

I read about a few board members doing differential swaps. All of them I know of have bought a new / used / rebuilt unit. Do you really have to do this avenue or could I source the the clutches from a Limited Slip Differntial (for LSD ability) and a different pinion and crown wheel to change the ratio?

Assuming I rebuilt the diff myself, is this possible? I don't know much about the internal configurations for our diffs. I have to do more reading.

i am not sure about down under but bmw replacment ring and pinion are a mother to come by around here in the us, as for a clutch unit, somebody is bound to make one that fits in the bmw diff but it's probably hideously expensive and it would be cheeper to find a used diff with ls in a useful ratio

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Originally Posted by winfred

i am not sure about down under but bmw replacment ring and pinion are a mother to come by around here in the us, as for a clutch unit, somebody is bound to make one that fits in the bmw diff but it's probably hideously expensive and it would be cheeper to find a used diff with ls in a useful ratio

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thanks. thats what i wanted to hear, if it was cost prohibitive. If something is hard to find in the USA, then I have no doubt it's a lot harder to find here.

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Originally Posted by BigKriss

I read about a few board members doing differential swaps. All of them I know of have bought a new / used / rebuilt unit. Do you really have to do this avenue or could I source the the clutches from a Limited Slip Differntial (for LSD ability) and a different pinion and crown wheel to change the ratio?

Assuming I rebuilt the diff myself, is this possible? I don't know much about the internal configurations for our diffs. I have to do more reading.

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Kristian, this is the reason why we ask for a core in return for a quaife diff. I tore down about 20 of them a few weeks ago, including a bunch for E34s.

There are a couple of parts that can't be bought from BMW. As Winfred said: the ring and pinion. We stockpile gear sets for this exact reason. Shims are also critical AND impossible to come by as new. We have a few limited slip packs if you're looking for one. Everything else can be replaced, and things can mostly be put together on your own/with a hydraulic press (HIGHLY interpretable). Take apart only requires a few punches and dead blow/ball pean hammers.

The trick is pinion preload. Getting this wrong can lunch the thing. If you read Jeff Bidoli's writeup, he discusses how his recently rebuilt diff started to whine. I'll suspect why: the shop that did the work read TIS, which has some kind of ridiculous torque spec on it, and followed the instructions. Oops.



best, whit

thanks champion. it seems the best option would be for me to find a complete unit in australia.

yep Id say thats the only way to do it. get another known working unit and plug it in, the side seals can be replaced easily but once you get to messing around with the input flange and seal is where you can run into problems pretty quickly and ruin the unit. I got lucky and saved my unit before it trashed itself.