Z3 Diff ????

[badboye21]

Hi guys during the course of building my 320 cab m50 conversion. I bought a Z3 2.8 diff 3.15 My problem is at the time I bought the diff I read all that was needed was to swap the back plate from the e30 diff. I finally got round to trying to fit the diff today and the back plate from the e30 is to small.
Is the problem the diff is wrong for what I need or do I need a larger backplate??
cheers Malc

[leeparkes]

How many bolts hold the backplate on?

Edit.... iirc you should be able to use the Z3 backplate.

[maggspower]

How many bolt holes are there in the diff cover you have.

You need one with 8 holes, I suspect you have one with 6.

[Brianmoooore]

E30s came with two different sizes of diff. 325 E30s used a medium cased diff., the same as the Z3, but the smaller engined E30 variants used a small case diff.
If you need to swap it, you will need the cover from a 325 diff., but I don't recall swapping over the backplate when I fitted mine. As said above, I'm fairly certain the Z3 diff bolts straight on.
It's the 525e diff. that needs a change of backplate.

[jmc330i]

I used the Z3M diff, the backplate was fine, only needed to change the output shafts for 325i ones.

[badboye21]

thanks guys will count the bolts tomorrow but the back plate was a lot smaller will try and fit the diff withe the z3 backplate and see how I get on.

[rich318i]

Z3 has the same rear sub-frame as the E30. Z3 diff will fit

[leeparkes]

Im sure the Z3 backplate is better than E30 as it has more/bigger fins for cooling.

[Brianmoooore]

Z3 has the same rear sub-frame as the E30. Z3 diff will fit

Backplate bolts to the body, not the subframe, so similar subframes prove nothing.
It still fits though.

[Brianmoooore]

Im sure the Z3 backplate is better than E30 as it has more/bigger fins for cooling.

That's the Z3M backplate. Ordinary 2.8 Z3 LSD doesn't have the extra fins on the bottom.

[rich318i]

Z3 has the same rear sub-frame as the E30. Z3 diff will fit

Backplate bolts to the body, not the subframe, so similar subframes prove nothing.
It still fits though.

what other BMW's use the same rear E30 sub-frame and not the same back plate for the diff? cos the only ones i know of are the Z3 and E36 compact, all use that back plate for the diff

[Ianb]

I had this issue with my Z3 Diff. I originally used the E30 med case cover ( as i had already polybushed it ) and the E30 speedo sensor. This didn't work and i noticed that when i put the Z3 cover and speedo sensor on my old Med case diff the chopper struck the speedosensor and locked the diff ( when trying to turn by hand ). In the end i used the Z3 cover and speedo sensor ( careful, there are two types of speedo sensor on z3 2.8 ). This fitted fine and the speedo works. I did have to change the output flanges from my old diff into the Z3 one though as the Z3 flanges were too big.

[Motorhole]

Oddly enough, I've just fitted an E30 medium case backplate & speedo sensor to a Z3M clutch-pack LSD with no problems...

[randomspeedfreak]

is the Z3 diff a torsen diff rather than a viscus as the e30 lsds are?
or is that just Z3m?

[Motorhole]

iirc, the 2.8 Z3 had a a torsen diff, not sure about lesser models. Only Z3m got the clutch-pack type.

[BMW_E30vert]

so does that mean a e30 med case back plate wouldn't fit a z3 torsen diff?

[jmc330i]

so does that mean a e30 med case back plate wouldn't fit a z3 torsen diff?

No, it will fit, but you shouldn't need to fit an E30 backplate to a Z3 diff in order to use it on an E30. The Z3 diff will fit an E30. I know 100% that the output flanges need swapping for E30 325i ones if the Z3M diff is used, but the backplates don't.

[rich318i]

yeah the outputs are bigger thats it. CASE CLOSED lol

[Motorhole]

No, it will fit, but you shouldn't need to fit an E30 backplate to a Z3 diff in order to use it on an E30. The Z3 diff will fit an E30. I know 100% that the output flanges need swapping for E30 325i ones if the Z3M diff is used, but the backplates don't.

Indeed, only reason I fitted an E30 backplate to my Z3M diff is because I bought the diff minus the backplate! And Z3M backplates are over £200, versus £15 for a used E30 one...

[rich318i]

the Z3M is a finn diff setup with 4 long bolts not just the 2 . They used to be £130 now £250 cos the price of metal went up. they all fit dont know who this myth started

[badboye21]

Diff is in guys straight fit Thanks for the advice even the output flanges are the right size any one know what the best diff oil to use is ?? its a 2.8 z3 diff i believe it is lsd but not 100% sure. I have part number if any one can shed some light on it ( if I turn one of the output shafts the other turns the same direction which I was told a long time ago rightly or wrongly was an indication of it being lsd ).

[Motorhole]

Go to realoem.com and do a part no. search. iirc Z3 2.8 diffs are torsen differentials, a form of torque-biasing differential that should deliver the most torque to the wheel with the most grip at any one time. However, unloaded they should behave like an open diff so would have thought that turning one output shaft would result in the other one turning the opposite direction, just like an open diff! Aside from searching the part no. the no-doubt way of checking is to take off the backplate, take a pic and post it on here.

[badboye21]

had the back plate off before i fitted it i will do a search on the part number thanks.

[badboye21]

I have done a part search on real oem my part number doesn't come up think it maybe my fault not the fault of real oem lol
If i search for z3 diff i can find complete unit 33101428439 or it lists lsd internals for all z3 2.8 cars

the numbers on my diff are 1428438 7609L3.15
899804 06920016

can anyone shed some light on this for me??

[Motorhole]

Came across this on e30 tech forum, not sure how reliable the info is though and it is contrary to the info I've heard before about 2.8 Z3s having Torsen diffs. From this info, if your diff came from an early 2.8 Z3 (pre 1999?), it would have a 25% lock clutch-pack LSD, as per the Z3m. This would make sense if your diff behaved like a clutch-pack LSD when you tried turning the output shafts in opposite directions.

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

[Brianmoooore]

Clutch type LSDs operate in opposition to things like ASC and other stability type things, so any Z3 with these is likely to have a torsen type.
Torsen diffs. behave exactly like an open diff. in all the conventional tests, so take the back off and have a look. You should see several little gears in the form of a helix.

Writing to you lot from under the shade of a tree by a river bank in Metz, France - the first time I've had an internet connection for a week and a half!

[DanThe]

Came across this on e30 tech forum, not sure how reliable the info is though and it is contrary to the info I've heard before about 2.8 Z3s having Torsen diffs. From this info, if your diff came from an early 2.8 Z3 (pre 1999?), it would have a 25% lock clutch-pack LSD, as per the Z3m. This would make sense if your diff behaved like a clutch-pack LSD when you tried turning the output shafts in opposite directions.

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

That info is not reliable at all! There were a hell of a lot of Z3's produced with open diffs, some of the ratios are wrong also, maybe an american list?

[Motorhole]

Yeah Dan, that's an American list