E21 is limited slip

[Lowered and Louvered]

I have a e21 limited slip in my 2002, the gear ratio is different then my old rear end, can I change the ring pinion from my old rear end? Thanks Bob 

[danco_]

What ratio do you have now ?

 

 

What ratio

are you hoping for? 

 

 

 

 

 

We can solve your problems. Just give us more info to work with. 

 

Edited December 9, 2022 by danco_

[Russell74Fjord]

yes, converted my 3.90 to 3.64

 

Update:

 

Mine was converted at Metric Mechanic - Jim has some modifications he can also do to have the limited slip engage faster. He has lots and lots of experience. I have also read that the ring and pinions are always a matched set, so mixing and matching rings and pinions is not recommended. Will it work, of course, will it whine that a sumofabitch - probably.

Edited December 10, 2022 by Russell74Fjord
add picture

[visionaut]

3.91 ratio in the e21 LSD vs 3.90 ratio in the 2002 diff means they use different number of pinion gear teeth to get that different ratio…  

 

You can likely change what’s in your LSD but might need a non-2002 pinion source??

 

[Cabbage Fumes]

Small case is small case, regardless of source. Decide what gear ratio you want, find a set (here, eBay, etc), and get someone qualified to swap the gear sets. Spoiler, diff builders tend to charge more than you are probably expecting for this, so it might make more sense to find a diff already setup with the ratio you want. The only thing to watch for is the pinion splines. They could be fine or course, so you need a matching flange.

Edited December 9, 2022 by Furry Camel
adding more info

[TobyB]

Yeah, it's a time- intensive process to reset a ring and pinion, 

so it doesn't tend to be cheap.  It also makes sense to find a 

BMW shop, as they'll have the spacers and shims already.

 

As to the original question, can YOU set up a different ring and pinon

in a case- yes, IF you're methodical and careful.  But it's not like

changing a bearing in a transmission- you'll have to measure, measure again,

reshim, and check the contact pattern.  And potentially go through a 

few sleeves and seals, if you get unlucky.

 

The E21 manual is out in the interwebs, and it's the last BMW source for

info on resetting diffs the BMW way.  That said, lots of others 

(Toyota, for sure) use a crush- sleeve system, and they're all pretty similar.

So there are plenty of sources for info.

 

t

 

[Conserv]

A. The 3.90 diffs. (U.S. 1976 49-state versions only) have 39-tooth ring gears and 10-tooth pinions.

 

B. The 3.91 diffs. (E21 era) have 43-tooth ring gears and 11-tooth pinions.

 

C. The 3.64 diffs. (just about everything except Euro-spec tii’s and turbos) have 40-tooth ring gears and 11-tooth pinions.

 

Are those 11-tooth pinions (in B. and C.) the same part? Stated differently, assuming you’re willing to make the necessary adjustments, including shims, etc., to create a correct contact pattern, can you convert your 3.91 into a 3.64 by installing a 40-tooth ring gear in place of the 43-tooth gear? Or do you, realistically, need to swap in a ring-and-pinion set?

 

Thanks and regards,

 

Steve

 

 

[williamggruff]

To respond to your specific question directly, "can I change the ring pinion from my old rear end?" the answer is, "Yes, assuming you mean swapping both the ring AND pinion, along with the related seal, crush sleeve, and shims. As @Furry Camel noted above, you’ll need to have an appropriate input flange, but you could also get that from your old diff.”

[Son of Marty]

It may be easier to just shift you lsd unit into the other case using that ring and pinion, this will save you from doing a set up from scratch and can just adjust the contact pattern with the side covers.

[Lowered and Louvered]

Thanks folks, What I think you’re saying is send it to Korman

[jimk]

5 hours ago, Son of Marty said:

It may be easier to just shift you lsd unit into the other case using that ring and pinion, this will save you from doing a set up from scratch and can just adjust the contact pattern with the side covers.

Previous threads on swapping brought out the side covers that are needed are $$ because there is a width difference.  A drawing was provided to machine them.

[TobyB]

Quote

Or do you, realistically, need to swap in a ring-and-pinion set?

 

Always as a set.  Even if you have 2 seemingly identical sets, they're set up by the factory to run as

a pair, and there is a number scribed onto the pinion itself telling you what setup adjustment

from standard you need to make to make that gearset run together.

 

In addition, once the gears are set in the case, they run together in a particular way

such that changing one or another might cause a problem.

 

Hypoid gear teeth are really pretty darned complex surfaces to machine.

 

t

 

[Dudeland]

Make sure you have someone that really knows these things.  I got mine done and it is too tight(I think). Something is not rolling correctly and binding up when things warm up.

[Gordon]

I'm just try to wrap my head around why you would want to have your old gear ratio in your E21 LSD?

[Slavs]

I used to have a number of e21 limited slip diffs. As I recall they also came in a 3.64 ratio with limited slip. I had one on a 1977 320i which was very dangerous to drive in wet conditions. If you weren't ginger on the accelerator in slippery conditions, your tail would spin around to the front.

 

Back in the day these diffs were pretty cheap. I removed a few from cars at salvage yards for $75 each. To be frank, I never really cared for them for the street. They are plain dangerous in wet conditions.

 

I have a 4.11 long neck diff which was converted to limited slip by a very competent builder. I gave him a 3.90 limited slip I sourced from the wrecking yard along with a 4.11 open long neck. And, he did his magic and created my diff from the two for $900. That was about 15 years ago. Was it worth it ? No ! not really, not for the way I use my car.

 

You got to check your oil level in the LSD frequently vs. an open diff because the LSD runs hotter and goes through gear oil faster.