Open to LSD conversion - change ring and pinion?

[econti]

The only suitable LSDs for sale in the country are a 3.45 ratio small case for $600, or a built 4.1 85% medium case for $1100.

My question is, how difficult would it be to combine my 4.1 open with the 3.45 small case using my ring and pinion to make a 4.1 small case?
I've never played with a diff before but am very mechanically competent.

Or do I just save up for another week and buy the 85%? How would that drive on the street, I would imagine sideways?

[MINIz guy]

I'm curious on the same topic. I have a 3.45 open and a 4.44 LSD. I want to make a 3.45 LSD by swapping the ring gears and not touching the 3.45 pinion on the case.

I assume shims would be needed to fix backlash and gear pattern. Where would I source shims?

How would I fix preload?

[SkiFree]

Swapping ring and pinions from open to lsd pumpkins has been done for 40 years. Yes, you will need to re-shim and set lash. Shims can still be bought from BMWnorthamerica (i.e. your local dealer or favorite supplier). It's best to give them part numbers up front though (using realoem.com for numbers). Some thicknesses are NLA and require you to have a machine shop machine one down to spec.

Here's article I wrote a couple years ago you may find helpful (see table of contents for applicable info).
http://www.bmw2002faq.com/_/technica...tial-build-r74

[econti]

I'm curious on the same topic. I have a 3.45 open and a 4.44 LSD. I want to make a 3.45 LSD by swapping the ring gears and not touching the 3.45 pinion on the case.

I assume shims would be needed to fix backlash and gear pattern. Where would I source shims?

How would I fix preload?

You apparently can't combine 3.45 and 4.44 as the flange heights for the crown wheel are different (? just what I've been told).

Swapping ring and pinions from open to lsd pumpkins has been done for 40 years. Yes, you will need to re-shim and set lash. Shims can still be bought from BMWnorthamerica (i.e. your local dealer or favorite supplier). It's best to give them part numbers up front though (using realoem.com for numbers). Some thicknesses are NLA and require you to have a machine shop machine one down to spec.

Here's article I wrote a couple years ago you may find helpful (see table of contents for applicable info).
http://www.bmw2002faq.com/_/technica...tial-build-r74

Very helpful, thanks.
However I may have just bought a 4.1 medium case from America and it may be in the process of being shimmed to 40% then posted over here ;D

-edit: and if that doesn't work well enough then KAAZ 2-way here we come

[MINIz guy]

You apparently can't combine 3.45 and 4.44 as the flange heights for the crown wheel are different (? just what I've been told).




Very helpful, thanks.
However I may have just bought a 4.1 medium case from America and it may be in the process of being shimmed to 40% then posted over here ;D

-edit: and if that doesn't work well enough then KAAZ 2-way here we come

I hope that is not the case. There is just one part number for both automatic and manual transmission 318tis so the unit is the same. I also read that low rations are different than high ratios, but 3.45 is still considered high.