Rear Caliper Centralization

[daykrolik]

I am rebuilding the IRS on the '67 OTS I have owned for three years, consequently I'm not sure what previous owners may have inflicted on it. In any event, although the rear calipers are parallel to the discs and properly positioned fore and aft, they are both approximately .07 inches out of side to side alignment with the disc in the direction where addition of shims will exacerbate rather than correct the problem. Also, my car has no adapter plates, number C22859, as shown in the parts manual and workshop manual. It is, of course, possible that the car does not have the original differential and/or calipers. In fact, the expert who rebuilt the differential for me said he believed it might be from a somewhat later car. I hope one of you experts have a solution for me. Do I need the adapter plates and will they solve my problem? Do I have the wrong calipers? Should I simply have the mating faces of the calipers skimmed down? Any suggestions would be greatly appreciated. I would be glad to provide any additional relevant information.

[jag68]

I have a 3:31 diff sitting on my shop floor that I took out of a Ser III XK12 that I wrecked. It has threaded caliper mounting bosses cast into the hub piece, instead of having a separate part (C22859) that bolts through the hub for that purpose, so I suspect yours is a later differential. The differential appear otherwise the same to the E Type. The very earliest E Types may also have had something similar from what I've heard from anecdotal stories, but they are anecdotal stories. I've had bosses of Wilwood calipers used on a racing E Type milled thinner and it worked well. Taking .07 out of the bosses won't appreciably affect the strength of the caliper - they don't work very hard on the back anyway, and it is the simplest solution provided they fit otherwise. In my experience I've found it's not necessary to be a fanatic on centering the caliper, as long as it runs true and the pads don't drag. Buying part C22859 won't help you if your differential has the cast bosses, as it won't fit on - you would have to change the hubs to E Type hubs to use it. C22859 was simply an adaptor because the hub bolt pattern and spacing is different from the caliper bolt pattern.

[daykrolik]

Thank you so much for your reply. After some research, I've come to precisely the same conclusions. Not having an original diff or the adapter plate for comparison, I just wanted to be sure I wasn't missing anything. I know centralization is not really critical so long as, as you say, everything else lines up and centralization isn't so far off that you run into difficulty removing pads.