Shim Cobra brake calipers?

Shim Cobra brake calipers? Problem found!

I’m just finishing up a 8.8 build up with and Eaton differential, superior 31 spline axels, and cobra rear disks… only the caliper brackets are interfering with the rotors, unless I place a .080” thick washer between the mount bracket and the caliper bracket.

What gives? Has anyone else seen this problem? I’m not really concerned about it working, Baer brake installs regularly need shimming, but this is a first for me using Ford production brake parts.

ttt

Yeh, i've done Baer brakes and this is always the case... but I have done several GT rear disk swaps never needed to shim them. The M-2300-K instructions say nothing about it either, yet if I don't the caliper brackets rub the rotors and could bend the rotors if I mounted the wheels. I wonder if it has something to do with the Eaton diff? The axels are 31 spline Superior Axle replacements for a SN95, they should not be the problem. And, all other parts, housing, brackets, calipers, rotors, are Ford OEM parts???

I now know what the problem is!

The reason the axle sticks out further is due to the 31 Spline Eaton differential. Or rather due to the size of the crosspin. One call to Superior axle, and shazam! They knew exacly what it was.

The standard car crosspin is 3/4" diameter, where as all of the 31 spline diff's, Fords post '87 trucks 31 spline and aftermarket, use a larger pin. Either 7/8" (ford and some aftermarket) or a 15/16" crosspin. This locates the axles out .0625"-.0938" further on each side. I believe the Eaton must be 15/16" as my axles sit out about .080" longer.

That takes a lot off my mind... hope it helps the next guy doing a 31 spline upgrade on a disk brake car. Surprised more people out there hadn't had this problem.

Anyway, I found that I could not shim the full amount at the caliper as this would not leave enough room for the parking brake cables (they hit the caliper mounting bolts and would not even go in). Had to shim it at the adaptor brackets (where they mount to the axle housing).