So, anyone who has pushed the brake system in these cars hard knows how poor the system is. I run Wilwood front calipers on my car, and even so, i have noticed that the brake pedal engagement height was never consistent creating a very unsettling feeling for the driver. I road race my car and ever corner feels different. One corner and the pedal engagement would be high, the next it would be near the floor. I think i have finally discovered why this is.

I believe the problem to be that the OE PBR rear calipers have a kick-back issue. That is the pistons retract too far. This retraction is not always consistent, and this creates the random engagement height.

I found this by playing with my in-car brake proportioning valve. When i have the valve all the way forward, (limiting pressure to the rear) i noticed my pedal engagement was high. But when i put more pressure to the rear, the pedal height became inconsistent again. Clearly, its the rear calipers.

I would try a 2lbs residual valve to see how that works, but I'm replacing the my rear calipers with wilwoods so I dont know if ill need it anymore.

 

Called knock-back. The pistons are being pushed back into the bores due to side load causing deflection of the caliper mounting. The PBR calipers being a floating design shouldn't have this issue.

Check that the pins the caliper slides on are not corroded and are lubed.

Make sure that the rear Wilwood calipers don't have a fixed mount. Otherwise the knock-back will still occur.

RBob.

 

Excellent answer by Rbob... yes, knockback is an issue. It will normally present itself after you make a hard corner and side load the rear axle. The guys on frrax occasionally fight with it. I think c-clip axles may be worse about it... but Im not positive.

Im also not convinced our brake system is "poor". Outdated, maybe. I could lock up the stock brakes with summer performance tires, so the limiting factor was the tires, not the brakes. There's no ABS or anything in the system to complicate and fail. It's a very simple, effective system. The only issue is the factory rotors are small, but in an era where the biggest wheels were 15", that was just what would fit. There's not a huge difference in stopping power anyway. Most of the advantage to modern brakes is they can maintain a lower temperature. The factory front brakes overheat too quickly, but if you're not racing, they should be fine.