Brake re-assembly caution

[Craig245]

A friend brought over his GTRA and wanted to replace the rear axle seals. He took it apart with some guidance and threw away the "Panoz" seals and put in some good ones. After reasembly he wanted me to look at it because one on the rear brakes was dragging badly. At first I thought the rotor was warped, so I put a dial indicator on it and it had 0.060" TIR (total indicated runout). I checked the hub and it had 0.040 TIR. I seemed like the hub wasn't straight on the axle. It got my interest up so I started to investigate. When I asked how his "Pedal" was under braking he said that he pumped it once before each corner to get the pedal up. What he had was "Knock back", where the warped rotor bumped the caliper pistons back into the caliper. Yielding a deep pedal until the pad were back tight against the rotor. I continued to take it apart and found that the PO, or the PO's mechanic, did some bad things. First they tightened the hub to rotor bolts completely, preventing the rotor from floating. This is probably a common mistake for someone who has never worked on floating rotors. Don't do it, follow the direction and torque specs. The second error was that he installed the hat backwards. Even though it is a flat plate, it has an outside and inside. This was the cause of the runout and an easy mistake to make. The bolt ears on the hub have a radius where they protrude from the hub to make them stronger. The center bore in the hats are chamfered on one side only. If you install the non chamfered edge toward the hub bolt ears, the hat will not seat square. It will tighten up at an angle dependent on the order that the bolts where tightened. I turned the hub around and the TIR went to 0.002", perfect. Watch for this when you replace your rear rotors and hats. (I think the hat should be chamfered on both sides to prevent this, but they aren't.)

Craig