On both my Sierra's the poly diff mount and rear have always been very close to each other. But now on my re-shelled car it's even worse, the arb is really tight against the diff mount. The diff mount already has the countersunk bolts fitted and even has the thin plate between diff mount and diff removed to gain some clearance, but that is not even enough.

I just don't get why these aftermarket diff mounts are not designed with a bit more clearance. I think there might be some history there, as originally the poly diff mount was first designed by Mc2Racing in the US, for the Merkur XR4ti. That car doesn't have a rear arb that runs so close to the diff mount, so no issues there. I believe the companies in the UK producing these diff mounts simply copied the design one-on-one, while they could have made an update to it to fix these clearance issues.

I am unsure what to do with it, as I don't want to run the car without rear arb or with the stock diff mount.

 

Hi Marc, this is quite often the problem with aftermarket stuff, it seems that the people who make the part could never have trial fitted it to make sure it does actually fit ok.

 

the tolerances aren't there in the sierra as they are in more modern cars
even the front suspension can be out so that one set of wheels that fits one sierra will foul on another
been there, done that
the diff mount is another issue where some will fit and others won't
other than remounting the plate or making the holes to the flor move futher forwards i can't see an easy way out

 

Motorsport developments mount with 4x4 Cosworth rear ARB on my 5 door hatch.

I know I have a weird diff that may change the fitment but it will only move so far before the bolts hit the edges of the holes in the bodyshell.