Locked up differential on E30 325

[Costi]

Hi everyone,

I'm new here.

I've just finished a project on a E30 convertible 325.

I went to MOT and it passed, but after 2 miles my differential got locked. I can't spin the wheels at all.

I fitted a complete Z3 (2.8l) subframe, arms and suspension and LSD differential (3.38 ratio). I still have the M20 engine and gear box.
From what I've managed to find out the gear box ratio is 3.83.
I also have 17" alloy 10Js on the rear (could this increase in width destroy the differential).

Does anyone else have this sort of set up?

Would this set up destroy the differential just by driving it normally?

I'm also reading on a lot of forums that LSDs should not be checked on rollers when doing the MOT. Is this true?

I would really appreciate a bit of help here.

Thanks,

Costin

[Brianmoooore]

What do you mean by 'locked'? You can't turn the input shaft with both rear wheels off of the ground, or both rear wheels turn at the same speed when the input shaft is turned?
The diff. shouldn't be damaged by any of the above spec., and the diff. doesn't do anything when on a standard Mot roller. It's the centre diff. on 4WD cars that's damaged by a single axle roller.

[Costi]

Thanks for this.
Both wheels are not spinning at all, either when the car is in gear or not. At first, I thought that the hand break pads got stuck, but no, I put it in gear, plenty of revs and the car didn't move at all and I just burned clutch.
This happened when I was driving at 35 miles speed.

After I finished with the MOT, I've driven for 2 miles, and started hearing a grinding noise at the back. I thought that it was the hand break, but it turned out to be this.

What do you think about the set up ratio that I mentioned?

Thanks again!

[Brianmoooore]

"Differential" on a rear wheel drive car is two independent components in one case - the crown wheel and pinion, which turns the drive through 90 degrees, and reduces the engine RPM to wheel RPM, and the differential unit, which allows the two wheels to turn at different speeds when required.
When driving in a straight line the differential part does nothing - it's just a rotating lump of metal, with no parts moving relative to another.
The problem you have appears to be with the crown wheel and pinion (although the problem could be broken diff. bits jamming it).
The only way to find out what's happened is to first drain the oil (you did remember to put some in? You wouldn't be the first to forget), and see if it has metallic bits in it, then take the rear cover off and see what's going on.
You don't give any indication of the rolling radius of your tyres, but, with an E30 overdrive gearbox, a 3.38 diff. ratio is biased towards economy, rather than performance. Would be more suitable with a later (post E30) direct top gearbox.

[drakesmith]

Did you tell the MOT tester it had a LSD fitted?
Should of been road tested and not on rollers for the brake test.

[ChrisHC]

Did you tell the MOT tester it had a LSD fitted?
Should of been road tested and not on rollers for the brake test.

I have had a car with an LSD for many years, a roller brake test never caused any problem, I see no reason why it should.

[Brianmoooore]

If your brakes are imbalanced across the axle, a LSD will distort the brake test readings somewhat, and the LSD will be operating for a short time right at the end of the test. This should do no more damage to the LSD than if you pull away from rest on the road rather briskly, with one wheel on gravel.

[M3KUK]

I've never heard of this MOT LSD thing? I have put my E46 M3 through 14 MOTs?
And my 2 E36's before that.

[drakesmith]

Think it depends on the rollers. The test centre that I use to use tested the brakes individually and the tester said it will wear the clutches out so he used to road test it.

[Costi]

Hi guys.
Sorry for the late reply. I took the diff off the car. The input shaft doesn't spin at all, it seems to be stuck to the crown. The 2 output shafts seem to spin ok, so hopefully there isn't much damage.
I found a few small bits of metal when I removed the back case.

My rear wheels size is 235/40/17. The radius is 30cm. The old ones were 205/55/15 and the radius was 29cm.

The reason why I went for a 3.38 diff is because I have a M52 B28 TU and 320ZF which I plan to convert, but it will have to be next year. Any opinions on this set up?

[Brianmoooore]

The LSD assembly is the valuable bit. AFAIK, that can be fitted to a replacement open diff, which shouldn't be too expensive. The chances are that the pinion bearing has broken up and is jamming things solid.
Any knowledge of the car that the diff. (and 320ZF gearbox) came from? Both these parts can be damaged by a hard rear end impact on a BMW.
With the ZF 'box and those wheels you will have the equivalent of a 4.03 diff. on a standard E30, which puts it somewhere between the 3.91 used on a manual 325 touring, and the 4.1 used on the auto version.

[Costi]

The 320ZF gear box is not fitted yet
I bought it and I plan to install it next year.

Diff and gear box is from Z3 2.8l and the engine is from an E46 which I plan to turbo. I don't know anything about the history of the actual cars that they came from. The sellers said however that they were in working order.

I bought a 4.1 diff so I can use the car till I get the conversion finished.