Is it common for disc brakes to be unbalanced? - Team Camaro Tech
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post #1 of 9 (permalink) Old Jun 18th, 08, 05:12 AM Thread Starter
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Dean
 
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Is it common for disc brakes to be unbalanced?

I'm down to checking my rear Baer 12" discs for being unbalanced. Just wondering how common this is or if anyone has had to have them balanced?

Dean

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post #2 of 9 (permalink) Old Jun 18th, 08, 06:06 AM
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Re: Is it common for disc brakes to be unbalanced?

Rotors should be, but not always, balanced out of the box. Most machine shops can do this function.

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post #3 of 9 (permalink) Old Jun 18th, 08, 06:09 AM
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Re: Is it common for disc brakes to be unbalanced?

I would think matching brake rotors would weigh the same. All rotors (execpt for the $3,000 ceramic ones) are cast into a mold. They should all be balanced, or even. If it was a bad cast, causing one part of it to be too light, it would be very evident (missing metal).

I'm guessing your getting a vibration, and your trying to track it down?
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post #4 of 9 (permalink) Old Jun 18th, 08, 06:17 AM
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Re: Is it common for disc brakes to be unbalanced?

I'm working on a C-3 vette and I guess it was not too uncommon for the rotors/hubs to be un-true so there is a process to check it while installed on car which I'm about to do since in process of installing new rotors and bearings. In this case you tq. bearing down to 15ft. lbs. to fully compress it to eliminate play. Then you use dial indicator planted firmly on frame or some solid surface next to rotor. Then spin rotor and and you want to be less than .005 total runout. I realize it's for a vette but may help you determine if you're within acceptable standards side-to-side.

Don't forget to reset the bearing tq. afterwords.
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post #5 of 9 (permalink) Old Jun 18th, 08, 06:59 AM
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Re: Is it common for disc brakes to be unbalanced?

i have seen a lot of rotors thet were untrue out of the box. i, myself will cut a rotor if it is brand new. (especially NAPA ones) but that is not unbalanced, just untrue.

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post #6 of 9 (permalink) Old Jun 18th, 08, 08:46 AM
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Re: Is it common for disc brakes to be unbalanced?

Is it a balance your checking for? Or, is it a flatness (rotates true)?

I have seen good flat rotors go bad by having lug nuts not torqued down well. If you have one or two lugs overly tight, it can cause warping when installed. This would give you a pulsing sensation when braking, as opposed to a vibration when driving down the road.
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post #7 of 9 (permalink) Old Jun 18th, 08, 11:26 AM
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Re: Is it common for disc brakes to be unbalanced?

What he said - are we talking about weight/balance (like a wheel assembly) or if the surface is uneven/needs resurafcing.

I've never had a rotor balanced - I have resurfaced plenty. Every brake job, in fact, even off the shelf ones need it from time to time, esp cheap ones.

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post #8 of 9 (permalink) Old Jun 18th, 08, 05:53 PM Thread Starter
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Dean
 
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Re: Is it common for disc brakes to be unbalanced?

I'm fighting vibes from the rear end mph related. I've had a d/s built and balanced 3 times, new Moser rear end, new TKO etc...
I have had the wheels off the car up on stands running up to speed clutch in, neutrtal, in gear dosen't matter the vibes are still there, the rotors run true I was just wondering if the rotors themselves could be unbalanced.
Yes I have tried multiple pinion/trans angles as well, I'm just reaching at this point.

Only thing left is to have a GOOD driveshaft shop like Denny's build me one (balanced to more than 500rpm ) since the new rear came with a 1350 yoke, I'm running a 1310 right now and would need it shortened anyway.

Guess I'll have to take it easy to Carlisle again, the banner must be there!

Dean

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post #9 of 9 (permalink) Old Jun 19th, 08, 05:22 AM
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Re: Is it common for disc brakes to be unbalanced?

With all the rotating stuff checked and rechecked, I'd be inclined to look at the drive shaft too. I faught that one for quite a while as well, and it did end up being the drive shaft.

I'll throw this out too. If I remember right, the drive shaft needs to be balanced, but also, the drive shaft must be built right. I think it had to do with the yoke positions on the drive shaft. They need to be 90 degrees to each other, not inline with each other. I'm talking about the mounting yokes on each end of the drive shaft. If they are parallel with each other, they bulid up some harmonics when rotating, causing the vibration. I remember Hot Rod doing an article on this, maybe check their site. Also, for normal use, I think the pinion centerline and the trans centerline need to be parallel as well. For race cars, I think you have the pinion pointing down a few degrees from the trans centerline, there-by using the rotational torque of the rear end to line up the centerlines on hard acceleration.
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