Z4M Roadster Diff removal difficulties...

[jontZ4M]

Hi guys

I've run into a spot of bother. I am now thoroughly confused as to what to do.

I am doing a light underside refurb on my roadster which I picked up a few weeks ago. As part of the refurb I planned to remove the diff which is leaking from the front seal.

As long as I have the diff off the car, I am confident I can change the pinion oil seal.

Today I tried to remove the diff. The prop and driveshafts came off no trouble.

The problem is I can not get the diff off the subframe/car. With other types of cars I have dealt with before, you just unbolt the diff and it drops straight down on a hydraulic jack. This one seems more problematic.

First problem was I can't get access to the rear two diff->subframe bolts. No space. I tried the usual tricks of making up my own tools, but no joy.

My next idea was to drop the entire subframe down 2 inches to achieve more access to bolts. Before doing that I had a good look at the shape of the diff, and bearing in mind there is part of the subframe that loops under the diff, I'm not even sure how this diff can be removed. If I managed to get the rear bolts out, then I'm not sure the diff would have enough room to rotate and drop backwards through subframe. Even if it did, I doubt I could manage carefully manouvering a 55kg diff while laying on my back.(car is on blocks)

So at this point I give up with the idea of removing the diff and instead look at changing pinion seal with diff on the car. I've got access to the big pinion bolt but bearing in mind I'm lying on my back with very little space of visibility, I'm not sure I can even remove this bolt, let alone re-torque/thrust it.

All in all, I'm stuck and not sure how to proceed.

Questions for you guys please:

1) has anyone removed diff with car on blocks? How on Earth did you do it??

2) has anyone replaced a front seal with diff on the car and the car on blocks? How on Earth did you do it??

3) there is a possibility I may need to give up on this. If so, I need to get a garage to change the seal. Car is not roadworthy for all sorts of reasons at moment, so would need to be trailered. Do we think a local garage can do this or needs some kind of specialist? Anyone know somewhere suitable not too far from Ely, Cambridge?

Thanks a lot.

Jon

[Wassup]

Definitely possible, you'll need to jack the car up high as possible from the rear and lay it on stands.

Remove the rear anti roll bar. The two rear torx bolts will break free using a shallow 3/8" torx socket and then use an 11mm racket spanner to lossen further. The front 21mm bolt is best tackled with a decent impact wrench as swing space is at a premium.

Once the bolts are off, the differential tilts downwards from the back but is best supported with a floor jack. Caution, its heavy AF, I had to get another pair of hands to help.

Pinion input seal will be easier to work once the differential is off the car in this instance I reckon, just make sure you mark the input flange and 32mm nut, as it's crucial to ensure bearing preload.

[PDJ]

You could also just drop the whole rear sub frame and have all the bits blasted and powder coated

While it is all off the car you can clean and protect the bits above the subframe

[Beedub]

You could also just drop the whole rear sub frame and have all the bits blasted and powder coated

While it is all off the car you can clean and protect the bits above the subframe

this is the way i plan to do it on mine.

[Joycey]

Yeah, the rear diff is sat slightly off centre so it obscures bolts.

If my memory serves me well I undone the drive shafts removed all the diff bolts, the threads on the subframe bolts are long so you can drop it an inch, you will need to remove the roll bar to allow the diff to pivot round the subframe. I did this on my chest but not sure many people can cope with the 50+ kilos.

First M subframe I did on the ground, actually found it easier.

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Second time I used some hydraulic help

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[PDJ]

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On it's way back in

[PDJ]

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As can be seen the bushes put up a good fight but I won in the end

[Beedub]

i'm really looking forward to doing this.. ive got a gear-lab diff cover to go on ( larger capacity and better cooling + stronger) so i'm going to strip it all and polybush it , and while im their paint it all black because i'm a tart.

https://www.ebay.co.uk/itm/165408280270 ... qQQAvD_BwE

[jontZ4M]

Wonderful feedback thanks guys!

I don't want to fully remove rear subframe yet as that will be next year's project.

Ok I'll get the tools and get cracking on removing diff

I'll probably rig something up to help cradle the diff as she drops.

Yup aware of the crucial pinion nut thrust.

[jontZ4M]

I just bought these Torx spanners hoping they will aid access to those nasty rear bolts: https://www.ebay.co.uk/itm/154309134846 ... BMiOPd98lh

[Wassup]

i'm really looking forward to doing this.. ive got a gear-lab diff cover to go on ( larger capacity and better cooling + stronger) so i'm going to strip it all and polybush it , and while im their paint it all black because i'm a tart.

https://www.ebay.co.uk/itm/165408280270 ... qQQAvD_BwE

I've gone down the Ecs route for differential bushes and OEM for subframe, didn't fancy the additional NVH from polybushes on subframe. Each to their own I guess

[Wassup]

I just bought these Torx spanners hoping they will aid access to those nasty rear bolts: https://www.ebay.co.uk/itm/154309134846 ... BMiOPd98lh

I still think you'll need a torx socket to access the bolt as it's recessed into the bush. Spanner will come handy once the bolt has been loosened.

From memory, Halfords sell them separately in store although you'll need to find a larger halfords store.

[jontZ4M]

I still think you'll need a torx socket to access the bolt as it's recessed into the bush. Spanner will come handy once the bolt has been loosened.

Yeh I've got torx socket set. On my roadster there isn't enough room to get the socket and head of the ratchet in there.

So I modified the socket by cutting 10mm off front, 7mm off back and 7mm off ratchet square insert. Total size reduction 17mm, still won't bloody fit in there! Trying spanners.

Question to you guys:
- what type of paint did you use on diff and subframe?
- how on earth do you clean up the alloy part of the diff? Wire brushes won't fit in this nasty crevaces.

[john-e89]

I still think you'll need a torx socket to access the bolt as it's recessed into the bush. Spanner will come handy once the bolt has been loosened.

Yeh I've got torx socket set. On my roadster there isn't enough room to get the socket and head of the ratchet in there.

So I modified the socket by cutting 10mm off front, 7mm off back and 7mm off ratchet square insert. Total size reduction 17mm, still won't bloody fit in there! Trying spanners.

Question to you guys:
- what type of paint did you use on diff and subframe?
- how on earth do you clean up the alloy part of the diff? Wire brushes won't fit in this nasty crevaces.

Whip it off, pop it in the post to me and I’ll vapour blast it if you want Jont, this is a cosworth diff I did the other day.

[john-e89]

The back plate I'm meaning.