Have a first gen race car that was converted to disc brakes on rear. They need to be rebuilt, how do I if the calipers are for a 12A or 13B? Is Black Dragon the best place for kits? Can't find anything local.

 

I believe that the GSL-SE (13b) brakes are all vented discs whereas the 12a brakes are solid discs as far as the rear axle goes. That is how you should be able to tell which calipers you've got. Also, the bolt pattern between a 13b and 12a rear end (SE compared to everything else) is different - SE has 4x114.3 and the others are all 4x110. So if you've got the same stock wheels on the whole car you can easily assume it's a 12a rear end.

 

The quickest way to identify 12A vs 13B discs and calipers is to measure the wheel bolt pattern, listed in the prior comments. That is assuming your discs have not been redrilled for a different wheel bolt pattern. Look for 2 sets of stud holes as an indicator.

The discs were different diameters between the 12A & 13B. Your shop manual can give you the specific dimensions.

The 13B only had front vented discs, the rear were solid discs.
Wheel bearings, front & rear, were larger on the 13B, and the front struts had larger diameter axles for the larger bearings.

Steering was identical.

The 13B engine is about 3/4" longer. The 13B front cross member difference was simply the 3/4" longer tab for mounting the front of the engine. The additional length was simply moved forward on the front mounts. If you have a 13B front cross member and want to mount a 12A motor, simply drill a hole 3/4 " back from the exiting hole.

If you are upgrading a 12A to 13B motor, you will have to fabricate a longer tab.

John

 

^Rear rotors on the GSL-SE are in fact vented. As mentioned, if you have lug studs it's most likely an SE, the GSL uses lug bolts instead (unless someone has converted to studs of course)

Also - moving this to the tech section