New brake rotor runout

[2autoX]

When installing new oe-spec front brake rotors, and the disc retaining screws are properly torqued, is it necessary to check the runout? If so, is the integrity of the hub what we are assessing?

 

[GregLocock]

You are checking that there is no grit on the mounting surfaces, or that the cumulative tolerances have not caused an out of tolerance condition, I think.

Certainly the factory doesn't check run-out after assembly.

Does the workshop manual actually specify that you do this? I suspect that if it does then it is making sure that you have actually cured the fundamental problem.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[2autoX]

Thanks for the feedback. It was actually Brembo, the mfr. of the discs, who specified the runout be checked. I also spoke with a gentleman who is a cart racer and he advised that the runout be checked because "rarely are they actually true from the factory." You guys have saved me from what had the potential to be an outrageously frustrating project.

 

[evelrod]

I have been using Brembo discs for some time now and I always check the runout after final assembly when new or when replacing pads...it's only a few minutes job, what's the big deal? I just like to know that they are within specs. Wouldn't it be better to find an 'out of spec' disc or assembly BEFORE you run it in?

Rod

 

[evelrod]

GregLocock (Automotive) 26 Oct 05 17:54
You are checking that there is no grit on the mounting surfaces, or that the cumulative tolerances have not caused an out of tolerance condition, I think.

Certainly the factory doesn't check run-out after assembly.

Sorry, Greg. I did not see this thread until this morning. Isn't it SOP to have the occasional quality control check?
Perhaps it's because the "QC" folks were on coffee break when my Canadian built '95 Chrysler LHS came through with the 'totally out of spec' brake rotors. Thanks to a good warranty, all four were replaced by <6000 miles. FWIW, the OE discs on our '01 Lincoln are still doing fine at 130,000 miles.

Rod

 

[GregLocock]

No, they'd never get checked unless someone noticed a problem on the assembly line or during the test drive. We don't disassemble finished cars routinely.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[izzmus]

It is important to remember that you are not taking the rotors directly from the manufacturing line to the car. They get shelved, crated, shipped, dropped, folded, spindled, and mutilated by a small army of mostly indifferent people in the interim.

For example. it is not uncommon for deliverymen to drop rotors from waist height to the ground to save their backs, or for them to store or ship rotors on end. Yes, this is a human problem, not an engineering one.

 

[Tmoose]

"Your minivan needs a new hub, and replacing the hub will destroy the bearings. It has excessive clearance, and that is why the brakes are "bumping" when the car comes to a stop."

Excessive clearance proved to be excessive wheel/rotor runout, and the same (otherwise acceptable) dealer had done wheel bearings about 6 months before. Further inspection on Satruday morning with everything still assembled revealed a huge hammer dent on the hub OD that raised a big (0.010 inch)lump on the hub face, which tipped the rotor and wheel. It seemed quite likely that the dent was an artifact of the wheel bearing replacement.

Within the first 100 miles after the bearing change one wheel's lug nuts were loose, and now I'm thinking that was the lump wearing down a bit.