I get a metallic 'clunck' on my Sapph when I drive off. I am quite sure this is caused by the rear arb touching the poly diff mount. Last year when I was rebuilding the car I didn't put the rear arb on, as I already saw it would be touching the diff mount and then it didn't make the noise yet. On my old car the arb and diff mount were also tight, but I never had any noises coming from it. So in the end I decided to put the arb on and see how it would go.

But I'm not quite sure how to solve this. The problem is basically with the poly diff mount being too 'thick' in combination with tolerances on the shell. The diff mount is an old one from Mc2Racing, from before they were available from the UK. The mount has the flush kit fitted as well (which is now standard on all mounts anyway), plus I already removed the plate between the diff and the poly bush to gain some room, but that is still not enough.

So what to do to get more room? I'm not sure if the diff mount can be made thinner in some way. I also was thinking of having a few mm milled of the backplate of the diff where the 2 bolts go in. But I'd rather not modify original parts to make aftermarket parts fit...

 

I would take more metal off the billet diff mount if you can. Can you do a picture of the mount in relation to the bar?

 

Today I had the alignment done and while it was on the 4 post lift I had a look underneath to take a picture. It turns out the arb is only touching the diff mount when the suspension is on full droop. When it's on its wheels there is about 1 - 2 mm clearance. Unfortunately the picture I took was blurry because it was too dark.

So I'm not sure where the noise is coming from, but I also didn't hear it today... I will keep an eye on it whenever I drive it again.

 

Is it worth putting some paint on the mount where you think/thought it was impacting? Take it for a drive, hope it clunks, then take a look for any chips/marks on the paint?

Sure theres a better product than paint, but its cheap and easy. Almost like you need plastigage

 

That's indeed an idea. But for now I'll first check if the noise is still there. But the 6 degree beam has rose joints on it, the arb has rose joints on it and the front tcas also have rose joints, so the car is not that quiet anyway.