188mm Diff Build, 3 Clutch?

[ckpitt55]

Did a search and found lots of stuff on how to do it, but not much on why. I'm going to be rebuilding / regearing my diff soon here and wanted to get some impressions from you guys that have added clutch packs to the LSD. I've only ever driven on the stock 25% lockup so unfortunately really have no intuition of what a 40% lockup would be like. I'm building the car for the street, but intend to do autox and DE's with it as well.

At what point does adding a clutch pack become advantageous, and how does its performance compare to stock? Is the car more prone to understeer on corner entry, oversteer on corner exit with throttle input, etc.? Or can that all be dialed out by adjusting carrier preload?

Thanks for any input

[Allona]

Subscribed

[ckpitt55]

In the hopes of getting a discussion going, I'll offer a thread and an article I came across

general workings of the lsd - http://e30performance.info/viewtopic...=explains+lsds

how ramp angles affect vehicle handling - http://www.intothered.dk/simracing/differential.html

[RobertFontaine]

How much choice is there in changing ramp angles with the stock lsd's?

[ckpitt55]

Short of having the existing ramps ground or adding additional ramps to the original thrust washers, I really have no idea. It was implied to me by several people I've talked to now that modifying the ramps is somewhat necessary when you increase lockup via additional clutches. Perhaps because the 45/45 profile no longer behaves like a 45/45?

[rarudduck]

Here is a link that explains ramps and clutches and their effect on handling. Ramps define how the lock is applied under dynamic situations.

http://www.intothered.dk/simracing/differential.html

[jbrannon7]

The Z3 M roadster comes with a 4 clutch zero pre load custom ramped BMW Motorsports diff that is awesome, unfortunately it is an E30 carrier. I replaced the clutches in mine at 60k and love the way zero pre load allows for great power off turn in. Very easy to "drive by throttle" in sweepers. I have a spare in my garage, one day I will take it apart and get photos. I know mcoupemindy has some photos but I can't find them.

Joe

[RobertFontaine]

Other than the z3m not having the ratio that you are shopping for can't the guts simply be transferred into the e36 180 carrier?

[Itsablurr]

Did a search and found lots of stuff on how to do it, but not much on why. I'm going to be rebuilding / regearing my diff soon here and wanted to get some impressions from you guys that have added clutch packs to the LSD. I've only ever driven on the stock 25% lockup so unfortunately really have no intuition of what a 40% lockup would be like. I'm building the car for the street, but intend to do autox and DE's with it as well.

At what point does adding a clutch pack become advantageous, and how does its performance compare to stock? Is the car more prone to understeer on corner entry, oversteer on corner exit with throttle input, etc.? Or can that all be dialed out by adjusting carrier preload?

Thanks for any input

In generalities, a 40% lockup build over a fresh stock 25%, all other variables being equal (ramps, preload, suspension, etc), will manifest as a slight improvement in braking stability before turn-in, and earlier throttle on corner exit. Your preload will determine neutral-throttle characteristics.

How much choice is there in changing ramp angles with the stock lsd's?

Infinite, whatever you want to machine into the pressure rings. Stock is 45/45 accel/decel. The pressure rings have space for a second set of ramps to be machined at 90 degrees from the stock ramps.

Short of having the existing ramps ground or adding additional ramps to the original thrust washers, I really have no idea. It was implied to me by several people I've talked to now that modifying the ramps is somewhat necessary when you increase lockup via additional clutches. Perhaps because the 45/45 profile no longer behaves like a 45/45?

45/45 will always behave like a 45/45. What they're altering is how the increased lockup potential effects the car balance upon accel and decel. Oftentimes, less lockup is desired on decel relative to accel ramps, so 30/60 ramps are cut, or 30/75, or 45/90.... options are limitless, and a higher numeric angle on a given ramp imparts less mechanical advantage applying pressure to the clutches for less relative lockup. All depends on what characteristics of the car you are trying to preserve or alter.

The Z3 M roadster comes with a 4 clutch zero pre load custom ramped BMW Motorsports diff that is awesome, unfortunately it is an E30 carrier. I replaced the clutches in mine at 60k and love the way zero pre load allows for great power off turn in. Very easy to "drive by throttle" in sweepers. I have a spare in my garage, one day I will take it apart and get photos. I know mcoupemindy has some photos but I can't find them.

Joe

As far as I've ever heard, and seen from cracking open my factory sealed MZ3 diff, that is not true. M Roadster and Coupe LSD units are garden variety BMW Motorsport with 2 clutch packs, 45/45 pressure rings.

Other than the z3m not having the ratio that you are shopping for can't the guts simply be transferred into the e36 180 carrier?

A 188 carrier is a 188 carrier no matter the case, so yes they can be transferred.

[z3papa]

Subscribed. I own two Jim Blanton custom built 188 diffs, one is in my car and the other sitting out in my office. It does wonders for putting power down in the corner over my OE torsen.

[ckpitt55]

In generalities, a 40% lockup build over a fresh stock 25%, all other variables being equal (ramps, preload, suspension, etc), will manifest as a slight improvement in braking stability before turn-in, and earlier throttle on corner exit. Your preload will determine neutral-throttle characteristics.

Would you consider this "slight improvement" to be a worthwhile one? What would you consider to be ideal for a balanced road race setup? (<< I realize that might be somewhat unreasonable to ask since diff configuration, wheel setup, suspension setup and load transfer, etc. are all co-dependent on each other).

Subscribed. I own two Jim Blanton custom built 188 diffs, one is in my car and the other sitting out in my office. It does wonders for putting power down in the corner over my OE torsen.

Willing to share any info on how these diffs are configured?

[jbrannon7]

As far as I've ever heard, and seen from cracking open my factory sealed MZ3 diff, that is not true. M Roadster and Coupe LSD units are garden variety BMW Motorsport with 2 clutch packs, 45/45 pressure rings.

I know my car came stock with the BMW Motorsports diff. I have taken it out, seen the build sticker, taken it apart, seen the 4 clutches and custom ramps, replaced the clutches and felt the zero preload. I have another factory stock Z3M motorsports diff in my garage and I was at mcoupeminy's when we took out and disassembled 2 more stock Z3M motorsports diffs. Every original Z3M diff I have seen or have first hand knowledge of is a BMW Motorsports diff many people think they are not because they jack up both rear wheels and can spin just one wheel, thinking it's an open diff or torque sense diff.

[Itsablurr]

Please provide some pics next time you have one open, because that is certainly contrary to my own first hand experience. Are you sure that you're not confusing 2 clutch discs and 2 dog rings as 4 "clutches"? Don't mean to be insulting or anything, but what you're stating is a very strange departure, especially if you found alternate ramps cut on the pressure rings. I'm sure that there is a logical explanation.

*edit: Pulled through some of Jonathan's old posts, and it seems that there were indeed some 'Motorsport' LSD units (4-clutch, 50/65 ramps, NO Belleville washer in the stack) that sporadically made it out in the late 90s or so, but without an apparent rhyme or reason, seemingly mostly across 3.23:1 applications. Consensus seemed to be that it was not a consistent application to the MZ3. I know the 3.15:1 from my '01 was a standard 2-clutch stock.

[z3papa]

I have 3 clutch setup with 40* ramp on acceleration, 90* on decel which allows dynamically more lockup during acceleration as the wheel speed difference increases, and no dynamic lockup on decel.

[eye145]

I think one of the more popular 188 set-ups that Dan at diffsOnline sells is the 30/90 ramps with 3 clutchs. I had emailed him and he recommended not putting a 4th clutch if that was the set up I was going to use.
I didn't ask about the preload though. I suppose that all depends on how the driver prefers the car to feel.

[BLAKE AuST]

I've got the 3 clutch kit from bimmerdiffs.com in my Frankenstein 318is trackcar(2.8lt,5sp,188type lsd), very easy to install, just open up, install, and torque back to spec.

I actually also bought a 2nd kit for my daily M3 3.0 euro

[B0rJarZz]

4 Clutchs (8 disks) with OEM ramps.

[Allona]

As the OP, I am also in the process of researching options to rebuild the LSD on my low budget track e36. Bimmerdiff.com 4 clutch upgrade seem cost effective, but it is a oem sprung setup and DIY kit. I also have the option of going with an "unsprung race" set up with Wanganstyle for extra $450 and he puts the LSD together.

I searched for sprung vs unsprung but could not find much, this is another consideration. I assume it mean removing the conical belleville washers. Can anyone share the how do the sprung vs unsprung feel? Performance advantages/disadvatages? Worth the extra $?

[RobertFontaine]

Swapping for a 3.46, installing the bimmerdiffs 3 clutch, ordering new parts for a rebuild all seems doable. Machining 1 set of ramps from 45 to 30. How steeper ramps are made for the other set of ramps is not as obvious. Can the existing ramps be rotated and the rings reused or is a custom piece required?

- - - Updated - - -

... will the rings from the porsche zf's dropin as easily as the spacers?

[ckpitt55]

So I tore my diff apart yesterday and started measuring stuff. I've had numerous guys tell me that 3 clutch setups were a touch on the sensitive side, some reporting problems with understeer and a rear end that likes to step out with throttle input without changing preload / ramps in the diff. I wanted to get an understanding of how much preload there is originally and how it could be affected with new parts.

I loosened the cap bolts evenly until they were no longer in contact with the cap. The gap between the carrier cap and the carrier is how much the stack is being preloaded by.



I measured from the top of the cap to the carrier



Then subtracted the thickness of the carrier cap flange



Resulting preload for my diff was ~ 4.04 mm.

Then I measured all my original clutches, dog plates, and the spacer. Stackup total was 11.78mm.

To predict a difference in preload with new parts for a 3 clutch upgrade, I assumed a new clutch thickness of 2.14mm (taken from Bimmerdiff's 4-clutch install guide) and ran calcs for each dog plate thickness offered on Bimmerdiff's website, ranging from 1.65 - 2.20 mm in thickness.

Below is a summary of my calculations. Without machining the carrier cap, I'm only able to reduce my preload by 0.41mm using the thinnest dog plates available.



From how I understand this, there's 3 elements at play here - if I am wrong in my understanding please correct me. I'm just a noob trying to understand this stuff:

• % lockup - amount of torque transfer available, governed by number of clutch discs, ramp geometry, and friction between surfaces.
• lockup "shaping" - governed by the ramps, controls how aggressively (or not) lockup is applied once the wheels start to slip
• lockup sensitivity - governed by preload, serves as a buffer for when the ramps start to actuate the clutches. More preload, activates sooner with less slip. Less preload, activates later with more slip.

Am I in the ball park?

What preload should I be shooting for with this if I wanted the additional lockup without it being sensitive to the point of interrupting the balance of the car? I've read of a lot of track guys liking very little or no preload for that reason - based on my measurements, getting near-zero preload would require the carrier cap to be machined.

[jbrannon7]

I do know that the BMW 4 clutch discs are thinner than the 2 and 3 clutch discs. We originally put standard BMW 2 clutch discs in my 4 clutch unit and it became a locker with so much pre load it was wheel hopping on turns.

[RobertFontaine]

Are the Ford Atlas and Volvo 1031 guts interchangeable?
With a little digging about through 188mm zf differentials it seems possible that appropriate ramps for accel/deceleration might be able to be simply ordered as oem parts.

- - - Updated - - -

Bmw part number for compression ring was 33141206909

- - - Updated - - -

30° thrust rings were available from bmw motorsports and zf directly. but they are out of stock now.

BMW Motorsports PartNr 33122224823
ZF PartNr 4061.306.501

- - - Updated - - -

The porsche zf thrust rings look to be 30*

[TheJuggernaut]

Does anyone know if the ramps are case hardened? Can I just take the thrust rings to a machinist and have him carve out the angle I want?

[Z3racer701]

They are, I've seen photos posted where e-bay specials didn't have the ramps and pin matched case hardened. They were just chewing through the ring, and not functional at all. You can have new ramps machined in, but be prepared to find a shop to do a rockwell test on the old ramp then match that level of hardness.

[TheJuggernaut]

Makes sense, thanks!