correcting rotor runout

[William F.]

Recurrent air in same driver's side front '67 brake. Think I have excess runout(previous owner changed rotor); first I'm going to measure runout. If it's excessive, should I have it corrected with one of the on car brake lathes such as Pro Cut or similar one by Hunter to take into account runout of whole assembly or can I just take rotor only off car and have it turned and get same results?
Thanks

[Edward J.]

Re: correcting rotor runout

Bill, I think you may have hit nail on the head, rotor run out will cause the pistons on the caliper to pulse in and out when applying the brake, hence taking in air into the system.

If you can find someone with a on the car rotor machine thats the best way. other wise remove the rotor and clean the hub surface where the rotor sits and have the rotor trued. you can also do the shim process if you want it truly correct , but this requires a dail indicator and the shims.

[Joe L.]

Re: correcting rotor runout

Recurrent air in same driver's side front '67 brake. Think I have excess runout(previous owner changed rotor); first I'm going to measure runout. If it's excessive, should I have it corrected with one of the on car brake lathes such as Pro Cut or similar one by Hunter to take into account runout of whole assembly or can I just take rotor only off car and have it turned and get same results?
Thanks

William------

You will very likely find that the run-out is caused by the spindle or hub. The replacement rotor will likely be VERY close to perfect out-of-the-box. So, to eliminate the run-out, you pretty much have to machine the rotor as an assembly with the spindle or hub (or, true-up the spindle or hub rotor contact surface).

[Gary R.]

Re: correcting rotor runout

Since the rotor was replaced I would go back and check the work done. Many times they're pulled out of the box and popped on the hub and that's it.

These were riveted on and once the rivets are removed and another rotor installed the 2 mating parts are going to be off.

Look for any rust or burrs on the surfaces. You didn't say how much runout you have? I set them up for under 002" and bolt them to flat surfaces. It works great buy takes time. With fronts you can machine them as a set if you deburr and bolt them on. You have to find someone who will just kiss cut them and then check them with a dial indicator that is fixed without any movement. Personally I don't like to turn vette rotors, new or used there is only 035 total of window to work with and an inexperienced or rushed operator can easily cut more then required.

Rears are more involved, fronts aren't too bad. Be sure the wheel bearings are properly setup as well.

[Joe R.]

Re: correcting rotor runout

Recurrent air in same driver's side front '67 brake. Think I have excess runout(previous owner changed rotor); first I'm going to measure runout. If it's excessive, should I have it corrected with one of the on car brake lathes such as Pro Cut or similar one by Hunter to take into account runout of whole assembly or can I just take rotor only off car and have it turned and get same results?
Thanks

Bill,

It's a piece of cake to turn the front rotors. ANY shop with a brake lathe can turn the fronts to very small tolerances. The bearing hub is left on the rotor when turned and therefore the center can be found very easily.

The rears are much more of a problem because they don't have bearing centers unless you turn them with the axles riveted or bolted on.

Like I said, any competent brake shop can fix you right up.

JR