Welding up rear diff

[Evoluzione]

Don't laugh (too much), but I've been asked if I will drop the rear diff from a '94 BMW 318s, weld it solid and put it back on so the guys can go do some cheapo drifting.

I just wondered if anyone can offer any advice on actually doing the job as it's something I've never done before (a car I'm not familiar with at all either), any potential stumbling blocks?

[Steve_D]

Stages required.
1. Draw up indemnity certificate and get it signed.
2. Weld diff.

Steve

[DarrenRGD]

You forgot
3. Stand back and watch it understeer straight into a ditch

[TheEnd]

http://en.wikipedia.org/wiki/File:Welded_Diff.jpg

[GavinPearson]

The first thing to determine is whether the differential gears are 'spherical', meaning whether the case is machined to leave a spherical surface on the inside that mates with plastic washers and spherical side & pinion gears. If this is the case, you need to remove the plastic & then machine dowels to peg the side gears in place during welding, or the shafts will never go back in afterwards. Measure the bore of the side gear to determine the size of dowel.

If the side gears have faces mating with the differential that are flat and have no side movement then dowels won't be necessary

There is the issue of welding cast iron, so brazing may be a better bet. We brazed the gears into place, then fitted new bearings.

After that it is simply a matter of rebuilding the diff assembly.

[bucksmanuk]

DarrenRGD said:

You forgot
3. Stand back and watch it understeer straight into a ditch

This, very much this....
I did this on my Mk2 Escort road rally car years ago.
Welding the teeth up is easy enough, decent arc welder should suffice - its what i did
Driving the car normally on the public highway in dry tarmac is difficult to put it mildly, and great for practicing half shaft changes when one half is left in the diff…..
With a large degree of “enthusiasm” on wet tarmac - its epic fun... like driving a big go-kart.

[Evoluzione]

Thanks for all the replies, I'm slowly forming a plan.

I think we've covered the general idea, I just need some Beemer specific info now like how to get the thing off and indeed, if I need to at all as it seems to have a cap bolted on the back. I'm wondering if I could remove that and do the job insitu.....

[TheEnd]

The rear case is usually part of the mounting, so awkward to get off just by itself.

They are easy to remove, the driveshafts have flat mating surfaces so once you undo the bolt, it'll slide down, you won't need to pull them out horizontally for a couple of inches to disengage.