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MG MGA - Disc/Rotor run-out

Can any of you guys with a worksop manual or other knowledge, tell me what the permissible run-out tolerance on the brake disc/rotors are?

I heve just put new ones on and one disc is 4 thou out and the other 9 thou out. I have a workshop manual but it only covers the drum brake set up.

As usual thank you all for your assistance.

Regards...John Bray
John Bray

Section MM of the later shop manual says run-out must not exceed .003 in. and that the discs can be ground up to a maximum of only .040 in. off the original thickness of .380 to .370 and that it can be equally from each side or more on one side.
John DeWolf

John,

With 9 thou run-out I would make some other checks. I suggest that you remove the discs and take measurements while off the hub.
Clamp the dial gauge to the disc mounting surface and run the pointer around the disc surface near the outer edge.
If these are new discs 9 thou is a lot.

Mick
Mick Anderson

John

Haynes MGA manual says .0006in (0.152mm) for a Dunlop type disc.

Steve
Steve Gyles

Steve,

That is only for the mga twin cam Dunlop disc brakes.

Mick
Mick Anderson

Thank you all for your comments, I followed Mick's advice and took everything apart again. I found measuring with the discs of the car quite difficult. So I cleaned everything up again and tried rotating the disc/rotors one bolt hole at a time. Eventually managing to achieve a run-out of 3 thou for bothe discs. The discs were new and genuine Lockheed ones, athough I purchased them about 20 years ago, and the greased paper they were wrapped in had stuck to the discs.

The excessive run out appears to be the result of using hubs that are 45 years old and it is now difficult to get a good clean interface on them where they attatch to the disc.

I have had enough of taking huns apart to get at the discs so will leave them as they are for now, until I'm able to drive the car. If I can detect any pulsing through the brake pedal I will have to look at the expensive option of new hubs.

Thanks again...John Bray
J Bray

This thread was discussed between 09/10/2004 and 10/10/2004

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This thread is from the archive. The Live MG MGA BBS is active now.