LSD Units - Ask me anything.

[iDreamBeemer]

When I had my 325i ('89) converted to manual Eko fitted a 2.0l gearbox.

My question is what LSD ratio would you recommend? I was hoping it would be 3.91...

From what I've read this would keep it pretty punchy - its a weekend toy now so want to lean more toward the acceleration rather than top speed but still want a little balance between the two.

(I also ask as the 3.91 seems to be the most common that comes up for sale, I've already got a wish list of rare bits and I don't want to add to it)

[Jimbob]

TommyM, that tag should should read 'S3.73' if it was a limited slip diff.

[TommyM]

TommyM, that tag should should read 'S3.73' if it was a limited slip diff.

Thanks wasnt sure as im not very clued up on them

[iDreamBeemer]

When I had my 325i ('89) converted to manual Eko fitted a 2.0l gearbox.

My question is what LSD ratio would you recommend? I was hoping it would be 3.91...

From what I've read this would keep it pretty punchy - its a weekend toy now so want to lean more toward the acceleration rather than top speed but still want a little balance between the two.

(I also ask as the 3.91 seems to be the most common that comes up for sale, I've already got a wish list of rare bits and I don't want to add to it)

Anyone able to answer this...?

[Demlotcrew]

Im sorry, I don't have much experience with M20 models, its very simple in theory but not that great in practice, I would be asking those who have actually done this conversion for their advice and results.

Andrew

[tomislav]

When I had my 325i ('89) converted to manual Eko fitted a 2.0l gearbox.

My question is what LSD ratio would you recommend? I was hoping it would be 3.91...

From what I've read this would keep it pretty punchy - its a weekend toy now so want to lean more toward the acceleration rather than top speed but still want a little balance between the two.

(I also ask as the 3.91 seems to be the most common that comes up for sale, I've already got a wish list of rare bits and I don't want to add to it)

Anyone able to answer this...?

4.10 lsd will be great on acceleration, 3.91 if you want it a little longer geared. I have run both in the past and there is very little difference between the two

[iDreamBeemer]

3.91 it is then! Ta

[DanThe]

Is there a 2.81 ratio CWP available in 210 fitment ala 8 bolt E36 M3 E34 M5 etc etc?

[vokietis]

Is there a 2.81 ratio CWP available in 210 fitment ala 8 bolt E36 M3 E34 M5 etc etc?

yes it is

[vokietis]

Hi, I am at the moment doing a m50 2.5 conversion, I am running a m42 box with the engine, what do you think would be the best lsd for all round performance?
Regards

3.91 4.10 4.27

[vokietis]

Here's another - how rare are 3.46 diffs?

mostly fitted to e30 323i,e34 524td autos and an e34 518i

[vokietis]

I've been told 3.15 LSD's are not too common..?

A gear ratio calculator...

http://www.bokchoys.com/differential/e4 ... ulator.htm

3.15 fitted to an e28 524 td,later e34 524 td manuals were fitted with 3.25 (same as e30 m3) or 3.46 if automatic

[vokietis]

apparently a z3m diff is a torsen diff.

have you any experience of this?

cheers,
matt

I have yet to see a Z3M with a Torsen diff, they are all 25% lock, 2 clutch preloaded units.

The 188type LSD from the Z3M uses larger 19mm bolts which are M14 and not the typical M12, you can make spacer sleeves that allow you to use this LSD with a regular E30 Crownwheel.

The other interesting point to make is that the Z3M uses a GrpN style LSD case, this represents it self with four large oval openings that allow significantly more oil flow to cool the clutches. This LSD cage also has a very slightly different designed 'cap' which does not need to be machined down anywhere near as much as the regular E30 cap when converting to 4 clutch plates.

Below is a photo of a regular E30 LSD case on the left and a E36/Z3M/GrpN LSD case on the right.



This photo shows a very very rare E36 M3 Differential which has 1.5way action with 45% on acceleration and 25% deceleration.



This photo shows a stock E30 ramp cage that started its life out at 45º and has been ground down to 30º.



Below is a Torsen type LSD.



HTH

Andrew

99.9% e34 525i sports (m50 engined) are fitted with four oval slots 3.23 ratio lsd units,also a late 324td and 524td with 3.25 ratio

[vokietis]

HI, IV BEEN TRYING TO WORK OUT WHAT DIFF I NEED FOR MY TOURING AS DOING A 328 M52 CONVERTION, IV BEEN TOLD E36TI`S HAVE THE SAME DIFF`S BUT ARE MOSTLY SMALL CASE,

THE OTHER THING IS HOW TO WORK OUT THE NUMBERS ON THE DIFF,, IS IT 3, WHAT EVERS ARE QUICKER WITH REVY TOP END OR 4. WHAT EVERS. ??/ WHITCH WAY AROUND IS IT..

m52 box?3.73 for track,3.25 for good everyday driving ;)

[vokietis]

half way though my m52 conversion now. but have ended up sticking to the m40 318 touring box and diff..
what sort of drive will i expect to get, will i need to change the diff,,

same gearing as 318,but more power means much faster

[DanThe]

Is there a 2.81 ratio CWP available in 210 fitment ala 8 bolt E36 M3 E34 M5 etc etc?

yes it is

What cars were they fitted to?

[Osamam3]

Is a 3.25 LSD good for a b32 road car ? I mean in terms of say staying at 3 k revs at about 80 and a good top speed ?

[Brianmoooore]

apparently a z3m diff is a torsen diff.

have you any experience of this?

cheers,
matt

I have yet to see a Z3M with a Torsen diff, they are all 25% lock, 2 clutch preloaded units.

Z3 2.8 is the one with a torsen diff. 3.15, IIRC.

[vokietis]

Is there a 2.81 ratio CWP available in 210 fitment ala 8 bolt E36 M3 E34 M5 etc etc?

yes it is

What cars were they fitted to?

sorry its 2.93 , e34 540 manual

[vokietis]

Is a 3.25 LSD good for a b32 road car ? I mean in terms of say staying at 3 k revs at about 80 and a good top speed ?

what gbox?

[urfy]

Any questions about LSD configuration and possibilities?

Andrew

Hi, wonder if you can decide which diff to go for?

I am re-building my tech2 325i sport but going the 2.7 route using my 2.5 block, crank & flywheel have been lightened & balanced and I am using a E30 323i dogleg gearbox.

I have a standard sport diff (I thinks its the S3.91), a S3.73 & a S3.25, so which will do what and which one would be the best?

The car will be for road use and not tracked. Any advice will be appreciated.
Thanks
Ivan.

can anyone advise on this?

[gooseygander110]

Hi, You seem to know what you are on about......... I have a 3.9 LSD with all new bearings set up by Bexhill Gearboxes which I am now looking to sell or ideally swap for something a bit higher as I am now very close to starting a M60B40 V8 and 6 speed conversion. It is road legal but is also my track bitch....... I am looking for some advise on where to look for a good second hand one from someone trusted..... who might like to trade ? Also what sort of ratio ? Wandering 2.9 ? Also will have a 6kg single mass flywheel
All the best Gus

[gareth]

I can change the ratio on your existing LSD if it's a good one? Local too, I'm in Hastings

[gooseygander110]

well as i say .....it was rebearinged etc ......... There is some freeplay some where........not sure if gearbox or diff....... or prop ........ Quite happy to pop over to Hastings if you can sort it out ........ are you able to sort any backlash and generally give it the once over ? The power is only going one way ..........that's more !! lol so i want it all tip top ........ Mate if you can sort it all at a reasonable price ....happy to bring it over to you .......can you help on the propshaft ?
regards
Gus

[gareth]

There should always be some free play in the diff (backlash) but not too much... As you're local, feel free to swing over with it and we can have a butchers.
Re propshafts etc, I'm not really set up to help. Usually the only things to go are the guibo coupling and centre bearing, both are pretty easy DIY swaps

[gooseygander110]

Cool Thanks Gareth...... I'll be in touch

[rix313]

I asked this some where else but am on mobile so the search is a PITA. Can you use the crown wheel from a medium case open diff on an LSD unit??

[gareth]

Yes. As long as all parts are from the same casing size, they can be swapped. Not an easy job though...

[rix313]

Whats involved with swapping them then? Sourcing an open diff and using the CWP instead of buying a whole new LSD would be handy.

[gareth]

Mechanically it's just a case of disassembly and parts swapping... in practice the bearing preload and position has to be reset to give the correct operation of the bearings and the correct gear meshing. This is done with shims. All bits are available from BMW but it's no easy job.

[rix313]

I assume the information is available in order to do this? Are the shims expensive from BMW?

[DanThe]

There are some TIS instructions floating about on the net, dont have any links but im sure they have been posted on here before

[Demlotcrew]

You need very specialist tools to set preloads.

It's far from easy and if you don't know what you're doing, expect to waste money and a lot of time!

Best to give it to a specialist.

[gareth]

What they said!
Also yes, shims are bloody expensive! about £200 to stock up a full range. This is why i will freely admit to cleaning and re-stocking used shims wherever possible.

[Martin347]

A question; the "percentage lock" is not an accurate method to describe the amount of resistance as "percentage lock" relates to the engine power/torque. Therefore, isn't stating the breakaway torque a better measurement?

I ask this because as I understand it, 70% lock equals a breakaway torque of something like 120 ft lbf (160 Nm) and is thus 70 percent of the engine torque (160-170 ft lbf or 220-230Nm for a standard 325i). If I was to build a much more torquey M20 (or use another more torquey motor), the "percentage lock" becomes some smaller number (depending on the torque of the new engine that is). One would then think that the 2 LSD's are different as the % lock values would be different, when in fact they are exactly the same LSD. Therefore, to accurately compare one LSD to another, the breakaway torque should be stated instead.

As I said above, this is my understanding.

Interesting post. I have never heard of the % lock being worked out like this before. Its a shame the post hasn't been answered. I have allways wondered exactly how it is measured, preload is simple but % lock is more tricky.