Mythbusters: Z3M LSD variants

[Wanganstyle]

From reconfiguring a few Z3m LSD units for Fun cars I have found that the factory has delivered them with 2 types of clutch LSD from the factory.

Torsen is not usually shipped in z3m, I wouldn't be surprised to see one in a z3m though as Torsen is standard z3 spec.

TORSEN:


Most Z3m are Oem fitted a standard 188mm LSD unit just like USA e36 m3. This style unit first came
Out late model e34/early model e36.

This is a standard e36 common 188mm LSD Capsule from a 325i. Inside it is identical in function and setup as a e30 188mm clutch LSD capsule. If you can rebuild one u can the other, internals v similar, gearing standard interchanges.




Rare cars have a 4 disc unsprung (no bellvue washersprings)-semi Motorsports setting LSD capsule that has a asymmetrical OEM center section, this center is ramped for 1.5 way action: less lock on deccel.

These units are set v lax from factory and designed to prevent lock up when lifting off throttle- but do require much more frequent service intervals.

You can see the additional oiling groove and stamping for 40/25 action
Additionally the center spacing and guts stacking is completely different, so standard rebuilding procedure is moot with it.

Oem 4 clutch unsprung style should NOT be tested for lock up like
Normal e30/36 sprung units. Bmw does not have a listed procedure for servicing these units, they seem to be unofficial units

Cost of refresh would be double of a standard e30/36 LSD as 4 clutch plates and dog plates need replacement.

It's guts/DNA uncovered.







Wbs 188mm usually is large stud fastener. same 19mm bolt heads for ring gear but the hole in diff flange and threads in ring gear bigger size.
Holes in diff flange will be larger also

hardware size differences: M on top.



In the USA; Z3m, e36m 3.0 and 3.2 usually have fasteners Biggie sized.

Z3m diff can only take wbs ring gears or drilled/re-threaded standard ones.

Besides for these minor details nothing is that special, with internals as the clutches and steels are made of same material.

[demlotcrew]

I am unsure as to why these cannot be converted to the same preload configuration as a stock E30 LSD since after measurement the internal dimensions were identical between both.

Andrew

[Wanganstyle]

I am unsure as to why these cannot be converted to the same preload configuration as a stock E30 LSD since after measurement the internal dimensions were identical between both.

Andrew

Why would you want to?

It's setup good from the factory for lap times in 4 clutch 1.5 way mode

[The Dark Side of Will]

What's WBS?

[demlotcrew]

Why would you want to?

It's setup good from the factory for lap times in 4 clutch 1.5 way mode

It has no or very little preload and a very sudden "on/off" actuation after only a few hours of use, I would much rather have a preloaded 4 plate LSD with 30º ramps. Im not convinced of 1.5way LSD's. I love the high speed stability and braking performance of a 2 way. You simply use the throttle to control the LSD to your advantage. All E30 DTM race cars used a 2 way LSD.

Andrew

[Wanganstyle]

It has no or very little preload and a very sudden "on/off" actuation after only a few hours of use, I would much rather have a preloaded 4 plate LSD with 30º ramps. Im not convinced of 1.5way LSD's. I love the high speed stability and braking performance of a 2 way. You simply use the throttle to control the LSD to your advantage. All E30 DTM race cars used a 2 way LSD.

Andrew

Perhaps your issue with the unsprung factory 4 disc 1.5 way units is with 1.5 way then? You can change out the center ramps for a 2 way to have more feedback on the deccel-

I've raced with both sprung and un-sprung in the same car and different cars; the racing E30 I drive is non-sprung; its 2 way ramps 4 clutch discs setting; NOT a 1.5 way center.

with preload springs it would understeer a bit for the current chassis setup and have too aggressive transitions; the car runs no rear swaybar and 750 lb rear springs.

[Wanganstyle]

What's WBS?

wbs vin number cars (M cars)

[demlotcrew]

Perhaps your issue with the unsprung factory 4 disc 1.5 way units is with 1.5 way then? You can change out the center ramps for a 2 way to have more feedback on the deccel-

I've raced with both sprung and un-sprung in the same car and different cars; the racing E30 I drive is non-sprung; its 2 way ramps 4 clutch discs setting; NOT a 1.5 way center.

with preload springs it would understeer a bit for the current chassis setup and have too aggressive transitions; the car runs no rear swaybar and 750 lb rear springs.

Interesting, I am running 50nm rear coil over and 23mm ARB, 4plate sprung LSD with 45º ramps.

No understeer.

Here is a clip of me on the ring 8:31 BTG.

http://www.youtube.com/watch?v=P4XGwkR23bw

Andrew

[Wanganstyle]

This is 4 clutch disc 2 way stock 45deg ramps un-sprung.
no rear sway bar, car dyno-ed 154rwhp post race.
stock M20b25 with no cats, TMS chip. 400 springs front 750 rear; no rear sway bar.
2800 lbs weight

[demlotcrew]

Your track car weighs 2800lb? - Still quite a bit of understeer and did I see some shiftlock?

What sort of track day were you on? Looks like a bit the movie DeathRace2000.

Andrew

[Wanganstyle]

190 cars on 1.9 mile track is hilarious fun

Local NorCal series 24 hours of lemons; my first race of this nature. "$500" car budget not including safety; it's hilarious fun and good racing. And a great party

Car is caged with 22 gal cell, still has glass, both bumpers for contact and a bash beam in front to protect the night lamps.

Has a bit more weight to loose for next event. G260 gearbox inside is sloppy so I'd point some shifting gremlins to it; also the loose nut behind the wheel!!

Under steer is probably from no rear sway bar and lack of driver skills, did not try running a bigger rear bar yet.

I was actually hoping for more lock up on lift off deccel on the diff for some braking effect / drift blocking ability and may set it with a little more tension load from thicker steels or clutches (or both).

Next event in (Infineon) is usually rainy so perhaps will wait till summer button willow event.

Right now it's running a $0 cast off parts "lemons spec" diff built with random mystery clutch discs ( abandoned pile from full rebuilds with new internals); some better condition free discs. Even the case and bearings were donated parts to meet lemons rules for "upgrading". It's quite silly and ridiculous

G260 been removed and a zf sg320 is going in, should be a fun next race with less weight!

[e21boi]

Rare cars have a 4 disc unsprung (no bellvue washersprings)-semi Motorsports setting LSD capsule that has a asymmetrical OEM center section, this center is ramped for 1.5 way action: less lock on deccel.

Hey, any more info on that? I have got myself a diff probably from Z3, 168 mm, 4 clutch unsprung, 2 way action, numbers 4061004301 5005845 S25. There is big "R" stamped on the housing, and R3.45 something on a tag. There are no big spring washers installed.

Can't figure out if it is supposed to be this way or someone has been fiddling with the setup in the past? Or maybe this is one of those rare LSD's?

[TobyB]

not in a 168 housing.

M parts start at 188 mm...

t

[Wanganstyle]

Hey, any more info on that? I have got myself a diff probably from Z3, 168 mm, 4 clutch unsprung, 2 way action, numbers 4061004301 5005845 S25. There is big "R" stamped on the housing, and R3.45 something on a tag. There are no big spring washers installed.

Can't figure out if it is supposed to be this way or someone has been fiddling with the setup in the past? Or maybe this is one of those rare LSD's?

sounds like you have one of those rare open diffs that were standard in all 4 cylinder 1.9 z3's

[e21boi]

Alright dudes,

Thanks for your help!

Just got a reply from ZF authorised service partner here, they have sent me spare parts catalogue for my diff, and it looks like there was a modification of limited slip diff with 4 clutch discs and no springs.

It was quite a pain in the back to get info on this exact unit, so anyone who has the same type diff and looking for some info just drop me a message :]

I am not authorised to share the catalogue I got, however ZF transmissions were kind enough to send it to me, so another way to get this info is contact them directly.

Now the diff is being overhauled, hopefully if fits my e21 diff housing and next summer I will do some sideways driving while smiling a lot.