e30 318 Touring w/ e36 m3 engine - swapping original rear diff to '98 z3 m question

[EastCoastErik]

Hello. I recently purchased an '89 e30 318 Touring mid-project from a guy in CA (the car is CARB certified) and am finishing what he started. I bought Rosie with all sort of goodies the previous owner purchased but never installed. One piece is a finned rear diff. Rosie came with a rear diff from a '98 z3 M & the Garagistic adapter kit & magnetic drain plug. So I realized last night that the 318 rear axle flange is a different diameter than the z3 diff, the z3 is about 3/4" greater. It looks as if everything should match up except for where the rear axle connects to the diff. Does anyone have the correct rear axles for sale?

[roguetoaster]

You probably want flanges from an appropriate car as any decent axle can deal with an S50/2 even if you drive like an idiot with sticky street tires. IIRC E30 medium case flanges slide in.

Try to verify what axles you actually have first in case the PO changed them.

[EastCoastErik]

RogueToaster- Thanks. I need to ID what I have and double-check that E30 med case flanges fit my needs.

I'll do some brief research, this one has been covered many times. I'll search Z3 diff swap, E36 diff, axle flange, diff splines...

Also, I realize that the Z3 diff is not really an upgrade but a ratio change and the fins are mostly for show as I'm the only one who will see them.

[EastCoastErik]

One other question; is there a specific left and right side or are sides interchangeable?

[roguetoaster]

Left=right.

[EastCoastErik]

My existing axle, the flange that bolts to the diff is approximately 98 mm whereas the diff I'm installing has a flange diameter of approximately 113mm. Does anyone have a left & right rear axle for sale that has a flange diameter of approximately 113mm? Thanks

[EastCoastErik]

Hello. So, I've got it all set. Now it the speedometer is not working. I re-checked the sensor - it's pushed in all the way & the connection is good. The tac works. Any suggestions why the speedo isn't working?

[Vincenze]

A Z3 M differential uses the same black speed sensor as the E30 325i.

62168355008

A regular Z3 differential uses the blue speed sensor as the E36.

[EastCoastErik]

Thanks.

https://www.ecstuning.com/b-genuine-...r/62168357020/

I bought this speed sensor.

[Vincenze]

Thanks.

https://www.ecstuning.com/b-genuine-...r/62168357020/

I bought this speed sensor.

It doesn't show the Z3 M among the compatible models.

This one does. https://www.ecstuning.com/b-genuine-...r/62168355008/

[EastCoastErik]

Thanks for all the help.