Diff mounting?

[drjim]

Chaps

I am still building my track car (BMW E21 316), and have a load of bits off an ex Geoff Steele 323i including solid rear beam mountings. I was talking to Brian Long at a trackday in July, and he suggested that the diff should be solid mounted as well. It normally bolts straight to the subframe at its front end, and has a big rubber/metal bush at the back end that goes to the bodyshell. Presumably if I left it like that it would move around at the back end and break itself???

If I do need to solid mount it, that's quite good as the bush is knackered and a new one is £45!

Assuming that solid is the way to go I will fabricate a nice chunky metal thing using the original bush (replace the rubber with big circles of steel). I was thinking that I should reinforce the boot floor, and maybe build a brace to triangulate to the shock towers. I have a rear strut brace, and have seen setups which triangulate to the boot floor and double as a battery holder. I have a leftover piece of CDS rollcage tube that should weld in there nicely.

Am I thinking along the right lines??

Jim

[boyracer]

Generally the diff reacts to the torque and thumps into the underside of the body. I come from a scoob background, but never heard of any one breaking them. Probably not a bad thing to have it solid, though it will introduce a little more noise into the cabin, though if it's a dedicated race car I doubt that will worry you. If it's not adding much steel to triangulate the diff mounting back to the strut brace I'd say go for it, otherwise it's probably not necessary. If you laminated the floor where the mount bolts to that's probably fine enough. Solid's fine, unecessary weight isn't.

[drjim]

I had a closer look at the diff mounting situation yesterday, the existing rubber bush is knackered and would need to be replaced, so making a solid version of it will save some cash. The brace and tubing I have won't add much weight, and I need to relocate the battery anyway, so I'll go for it.

I'm sure I'll get some photos of the car online once it's finished!

Jim

[JamesH]

You could probably machine up some polyurethane bushes to replace the rubber - not quite as solid as steel/Ali, but would give some movement to prevent too much cockpit noise/problems with fatigue. Works for suspension arms....

James