Jag rear end vented brakes upgrade problem

[Akimbeau]

Since I had the rear end apart, I thought I'd up-grade the rear brakes to vented rotors, try to reduce the heat at the stub axles. The kit I purchased incorporates a 2 piece rotor...a vented rotor from Wilwood and a 1/2" steel hat that adapts it to the stub axle. With some minor spacer tweeks and a small bit of grinding on the calipers the kit seemed to be coming together. The surprise came when I found that one of the hats was severely warped..almost 1/16" across its surface. The other hat seemed fine. I called the company that sold it to me and they are sending out a new hat. In the mean time, I put a dial indicator on the "good" hat and rotor and found that it's run-out in relation to the diff was .014. I tested the stock rotor I removed and it had a run-out of only .003. What is your opinion on the higher run-out of the vented kit? Is it more forgivable because it is a 2 piece rotor, having more flex? I'd hate to get the rear together and back in to find that I get pedal vibration or some other problem from the higher run-out. I get the other hat tomorrow and will mock that one up as well and see what run-out it has.

Kim

[xb-60]

Kim,

Even 14 thou is way too much. Rotors don't have any significant 'flex'....so depending on how much run-out there is, you would have varying degrees of pulsing of the pedal.

Good luck!
Glen

[DanEC]

That doesn't sound good. Old 65 - 82 Corvettes have problems with excessive runout in rear rotors that have been replaced and not trued up. The rotors cause the pistons to work back and forth and pump air into the calipers past the seals - resulting in a soft brake pedal. This is in part made possible due to the design of the stock Corvette piston seals. But always a chance it might do the same with the Girling seals.

[joyridin']

.014" is too much. You are probably going to feel a pulsating in your pedal when you hit the brakes. You stated you checked the hat. Did you check the rotor after it was bolted on the hat? The outside edge of the rotor is probably going to be around .02" when you take the larger diameter into consideration.

[Akimbeau]

Originally Posted by joyridin'

.014" is too much. You are probably going to feel a pulsating in your pedal when you hit the brakes. You stated you checked the hat. Did you check the rotor after it was bolted on the hat? The outside edge of the rotor is probably going to be around .02" when you take the larger diameter into consideration.

I checked the run-out with the rotor bolted to the hat and the hat bolted to the stub axle. I'm thinking they just drilled holes in a round flat piece of steel, it doesn't looked machined at all. I've not had much machining done besides the typical engine rebuild type work. Do you think I can take these to a machine shop and they can turn them so they're flat?

[joyridin']

I do not know how think the hat is, but if it has enough material, .014" should be no issue. You may want to mark the high side and low side just as a precaution. Depending on how it is bent or warped, they may have to take a little from the inside and a little from the outside to get it to run true. Is the thickness the same all around the hat? Can you check?

Something else to consider. If you modify anything made by Wilwood and you have a problem later, you are screwed. Just a thought.

[Gaz64]

All parts to make brake components should be machined square to centreline.

Otherwise, how could you end up with technically zero runout?

.014 is insanely too much, and even .003 is too much.

The side with .003 could come down by indexing the rotor.

But both hub adaptors should have machined faces to start with.

[Akimbeau]

The adapters are 1/2" thick and zinc coated. Since one of the adapters was so wildly warped, about 1/16" across the 6" diameter, I'm thinking that they might be heat treating the adapters and causing them to warp. It's hard to tell if the adapter faces are even machined with the coating they have on them. I get the new adapter today so I'll mount it up and see what the runout is and make some decisions based on what I find. If the new one runs true I'll send the other one back and hopefully get a true replacement.

Kim

[Grubby]

I can usually feel .002 run out and change rotors.

A decent machine shop should be able to fix your issues.

John