Axle/Diff compatability issues

[Z3_GoCar]

It should have been a no brainer job....
I've got the axles that go to an e-36/7 Z3 2.8l and the Diff that's susposedly never been out of the car, but the inner CV doesn't mate to the output flange, as in the inner mating is too large or not deep enough for the the flanges inner mating. I'm afraid that I have ///M axles which are susposed to be 94mm. Is that the OD of the mating diamerter, or the bolt circle? I've ordered a new J/Y diff from an automatic 2.8l Z3 (4.10 ratio, but open diff) I hope the flanges fit, but it'd be nice to know before hand. I suspect that the e-30 flanges are different so I suspect that's where the problem is. Can anyone shead some light? Thanks.

James

[Doc Bro]

James,
2 things.

1. Are you sure that you have the stock diff in the car?
2. Are you trying to button this up in the car or have you removed the crossmember, final drive, trailing arm assemblies?

I have done this job several times. The last time I did it (2 mos. ago) I had a bear of a time getting my inner cv to match up to my output flange....I hadn't changed either one and I had unbolted them the day before. Try spinning the axel and aligning at each bolt hole...some times it takes persuasion. They seem to fit very particularly and can be finicky. I find it to be infinitely easier on the garage floor carrying the whole assembly as one unit.

....that is providing you have what you have been told you have....

(1.9l Z3 (or e30 318) stuff won't fit on any 6 Z3cyl stuff...the diameter of the output flange is too small....I'm sure you know this already but I thought I'd mention it anyway)

R

[Z3_GoCar]

Thanks Rob,

One things for certain, these axles and diff have never meet before. I've extensively looked at part numbers, so I also realize that the mating bolts are m10 for the medium and m8 for the small case. The bolt holes are definetly m10. So that leads me to wonder about any differences between e-30 flanges and e-36 flanges, along with the fear that my axles are actually m-roadster parts and not Z3. BTW, the output flanges on the all 6 cylinder (non-M) e-36's have the same part number, which is different than the e-30 part number.

I've been driving 4.10 gears at Laguna Seca in Gran Turismo. I set up a Z4 with similar specs and weight to what I'm expecting, including transmission ratios, and wow. The 4.10's a really good gear for there, I wonder about Button Willow if it'll be too short for some of the longer straights. I'm sure Willow Springs will require a 3.73 or even a 3.46.

[BMW RACER]

James.

First you might want to check on that 4:10 choice, I think it's going to be too short even for Laguna. Remember you have a 1 to 1 fifth gear. Look around Bimmerworlds web site, I think they have a gear chart you can plug in you gear ratios and tire sizes and it'll give you the speeds in gears.

As far as the flanges are concerned I believe that all the "big diff" flanges are interchangable. I'll double check the sizes when I get an E36 up on the hoist. But I know on the 325 it has a slightly smaller diameter flange.

Also speak to Rob Inthout (Kevin Mc Donalds landlord) about getting a limited slip.

[Z3_GoCar]

Oh Rob,

I forgot that this is all on the car. I've got pictures, but they're not in a place that I can post to them. If I remember right the inside of the flange is cylindrical with out any cutouts. The picture shows the back side metal cap just starting into the flange, but not any farther than the rounded endo of the cap so there like a good 7-10mm (1/4"~3/8") before the axle seats aginst the flange.

Hey John,

I factored the 1:1 fifth gear in, I did the calculations by hand, assuming no slip at the tire: I get:
Gear: 6800rpm 7000rpm

3.73 128.6mph 132mph
3.91 123.7mph 126mph
4.10 117 mph 120mph

I also saw the speed chart that covers all the gears, and not just the top gear at the Bimmerworld site. I worked it for a few minutes last night. In my simulation of Laguna I don't see more than say 117 anywhere on the track, and this includes the front straight into turn 2. Thanks for the pointer on where to find a limited slip.

[mlytle]

Thanks Rob,

One things for certain, these axles and diff have never meet before. I've extensively looked at part numbers, so I also realize that the mating bolts are m10 for the medium and m8 for the small case. The bolt holes are definetly m10. So that leads me to wonder about any differences between e-30 flanges and e-36 flanges, along with the fear that my axles are actually m-roadster parts and not Z3. BTW, the output flanges on the all 6 cylinder (non-M) e-36's have the same part number, which is different than the e-30 part number.

I've been driving 4.10 gears at Laguna Seca in Gran Turismo. I set up a Z4 with similar specs and weight to what I'm expecting, including transmission ratios, and wow. The 4.10's a really good gear for there, I wonder about Button Willow if it'll be too short for some of the longer straights. I'm sure Willow Springs will require a 3.73 or even a 3.46.
[/b]

the "m" axles are very different that the stock ones. the diameter of the actual axle is MUCH thicker. easy to tell visually if you have one of each in your hands. the flanges on the axles should be the same for either. the axles are interchangeable (at least on the regular e36's).

of course, the m axles would be illegal in ITR..

[GKR_17]

In my simulation of Laguna I don't see more than say 117 anywhere on the track, and this includes the front straight into turn 2.
[/b]

When you say "simulation", do you mean running a few laps on the Playstation, or is it something more sophisticated? Just curious.

Grafton

[Z3_GoCar]

I received my new diff this evening, and just got back from delivering it. It's definetly got cut-outs for the rear cover on the inner C-V joint. I suspect that the one in the car could be from an e-30 as the medium diff from the e-30 325 is shared with the six cylinder Z3, the flange for the e-30 is different and I suspect that its not got the cut-outs.

Graffton,

PS-2 GT-4 has the Z4, I've changed the transmission to the variable gear then adjust each gear ratio untill it lines up to the stock Z3's 1st - 5th. I leave 6th alone as it winds up being way too tall anyway. Lap times are in the realm of feasible, and seem close to actually being achievable, although I probably won't this season.

James

[robits325is]

It should have been a no brainer job....
I've got the axles that go to an e-36/7 Z3 2.8l and the Diff that's susposedly never been out of the car, but the inner CV doesn't mate to the output flange, as in the inner mating is too large or not deep enough for the the flanges inner mating. I'm afraid that I have ///M axles which are susposed to be 94mm. Is that the OD of the mating diamerter, or the bolt circle? I've ordered a new J/Y diff from an automatic 2.8l Z3 (4.10 ratio, but open diff) I hope the flanges fit, but it'd be nice to know before hand. I suspect that the e-30 flanges are different so I suspect that's where the problem is. Can anyone shead some light? Thanks.

James
[/b]

Those output flanges pop off with a big screwdriver in about 15 seconds. Swap the flanges from one diff to another and you are all set.