who knows diffs?

[evandael]

i pulled a diff from an m52 equipped z3. it has a sticker identifying it as a 3.15 (confirmed via flange-rotation method) and a painted 'R' on the top, which signifies it is a Torsen-style unit.

however, i finally drained it and pulled the cover today and it looks like this (not my pic, but is identical in appearance)



or this




basically, it's a clutch-type limited slip. this would be all well and dandy, save for the fact that i can rotate the output flanges opposite one another with only a moderate amount of hand force.


so first; did some z3's (non-M) come equipped with clutch-style differentials? i can't find any definitive document that shows they did.

and second; because i can break the clutches loose so easily, am i looking at a rebuild?

[future rs]

I believe these have to have fluid and a certain amount of torque to "lock".

[reelizmpro]

Not all z3s had torsens. I thought it was the m versions that had em but it may have been the 2.8. I am not sure.

[b*saint]

Doesn't look like a clutch pack imo. You should see a hardened pin about 14mm in diameter sitting between two V's (ramps.)

[evandael]

^keep in mind those photos are of actual LSDs, not mine (though mine is identical in appearance)


i just want to know if some z3's were equipped with clutch-type limited slips, and also if a worn LSD exhibits the behavior i mentioned earlier (ability to turn output flanges opposite by hand)

[SkiFree]

if a worn LSD exhibits the behavior i mentioned earlier (ability to turn output flanges opposite by hand)

Yes.

3 Break away:-------------------------------------------------------
Prior to disassembly, measure the break-away torque of your differential (how much force it takes before the LSD clutches slip). A good percentage of the used E21 LSD's out there today are worn to the point where they hold barely more than a sticky open diff (sorry for those of you who paid $400 for an non-inspected E21 LSD). If you can twist the differential out-put flanges in the opposite direction with your hands then you've got a very worn differential. A healthy stock e21/e30/e36 small case LSD should take between 25-30 ft/lbs before slipping. By measuring now, it will give you a good baseline indication on the condition of the individual components inside the center pumpkin.
I measured my E36 pumpkin to have a break-away of 26ft/lbs, so technically I would be ok if I was to just stick it into the case and call it a day. However, I'm shooting for a bit more than 40ft/lbs. which is about the most I'd want out of a street-oriented LSD. (by comparison SPECE30 medium case LSD’s are limited to 65ft/lbs., and most other 2002 race setups are around 80ft/lbs.)

A weak limited-slip (with a low break-away) is simply due to a lack of tension on the internal components i.e. low break-away = worn internal parts = lost material = more space in case = less tension under load.

from

http://www.r3vlimited.com/BOARD/showthread.php?p=3369555#post3369555

[evandael]

right on. thank you.

i am now considering swapping the internals from my good 3.73 to the 3.15.

my assumption of the process:

remove output flanges
measure gear lash and wear pattern
remove and swap limited slip units
swap ring gears before bolting unit back in place
shim as (or if) necessary for side-to-side movement and preload

now this is where i am concerned.. because the ring and pinion wear as a matched pair, do i also need to swap the pinion gear? meaning i also need to swap the pinion bearing?


OR, am i creating too much work for myself, and all i need to do is swap the actual locking unit internals? and of course make sure the gears mesh as before, with the same side-to-side movement/etc.

[Varinn]

You cant use the pinion gear from a different ratio, meaning a 3.73 ring does not work with a 3.15 pinion. If you wanted to do an internals swap, you'd be best off to put all of the parts INTO the box that started with the ratio you want to run.

[robrez]

The Torsens are specific to the non-mZs circa 1999 model year and forward. Here's some info. I've gathered.

Torsen units:
Z3 M52tu 2.5 Manual 3.15
Z3 M52tu 2.5 Auto 4.27
Z3 M52tu 2.8 Manual 3.15
Z3 M52tu 2.8 Auto 4.10
Z3 M54 2.5 Manual 3.46
Z3 M54 2.5 Auto 3.64
Z3 M54 3.0 Manual 3.07
Z3 M54 3.0 Auto 3.46

Clutch Packs:
Z3 M52 2.8 Manual 3.15
Z3 M52 2.8 Auto 4.10
Z3 S52 3.2 Manual 3.23
Z3 S54 3.2 Manual 3.15

http://www.kneb.net/bmw/E36-7/SI_00_77_98_Z3_coupe_2.8_and_M_coupe_Introduction.pdf

http://www.unofficialbmw.com/images/diffassignchart.jpg

[evandael]

If you wanted to do an internals swap, you'd be best off to put all of the parts INTO the box that started with the ratio you want to run.

so to clarify.. i can swap the guts of the limited slip units between the two diffs (good clutches from my 3.73 > my worn 3.15 and vice versa)?

The Torsens are specific to the non-mZs circa 1999 model year and forward. Here's some info. I've gathered.

Clutch Packs:
Z3 M52 2.8 Manual 3.15
Z3 M52 2.8 Auto 4.10
Z3 S52 3.2 Manual 3.23
Z3 S54 3.2 Manual 3.15

http://www.kneb.net/bmw/E36-7/SI_00_77_98_Z3_coupe_2.8_and_M_coupe_Introduction.pdf

http://www.unofficialbmw.com/images/diffassignchart.jpg

awesome, thanks. i had not seen that information in any of my internet searches. my diff came from a m52/manual equipped car.

[Varinn]

Who you really want to talk to is Wanganstyle or Jlevie (who seems to be the king of e30 knowledge around here). As far as I understand it, you can pull the entire carrier assembly from one differential and bolt your ring gear to it then re-install in the same diff the gear came from. This keeps the pinion gear untouched, and all you'll have to do is likely swap the output shaft bearings and re-shim with the correct pre-load and clearance/backlash on the teeth.

[SkiFree]

Who you really want to talk to is Wanganstyle or Jlevie (who seems to be the king of e30 knowledge around here). As far as I understand it, you can pull the entire carrier assembly from one differential and bolt your ring gear to it then re-install in the same diff the gear came from. This keeps the pinion gear untouched, and all you'll have to do is likely swap the output shaft bearings and re-shim with the correct pre-load and clearance/backlash on the teeth.

Yes, this is exactly what I've outlined in the provided link.

[evandael]

Who you really want to talk to is Wanganstyle or Jlevie (who seems to be the king of e30 knowledge around here). As far as I understand it, you can pull the entire carrier assembly from one differential and bolt your ring gear to it then re-install in the same diff the gear came from. This keeps the pinion gear untouched, and all you'll have to do is likely swap the output shaft bearings and re-shim with the correct pre-load and clearance/backlash on the teeth.

ah okay. it seems there may be more than one way to skin this cat. luckily I've got some time to figure out which way is best.

[evandael]

also, skifree, I just saw your post. excellent information!

[Varinn]

Yes, this is exactly what I've outlined in the provided link.

Damn! Sorry I didnt even click your link, that is an absurd level of detail that I have not yet come across before. What BMW manual were you using that goes into detail on the proper technical specs? I'd like to do a little personal research to see if the BMW setup is the same as the specs listed in my millwright manual for a matching gearset. As far as I can see it, automotive diffs are no different than an industrial gearbox, hypoid, bevel gears etc can only be so different from one another. I'm debating my own diff swap/build but have a bit of fear about setting things up correctly as I've only ever done it on worn out classroom gearsets.