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Brake Rotors Out-of-Balance...BAD!

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Old 03-18-2005, 08:14 PM   #1
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Default Brake Rotors Out-of-Balance...BAD!

Here's something most people don't know.

Brake rotors can be out-of-balance so bad that it feels like the tires are out. AND there is NO VIBRATION DURING BRAKING.

I know. That's the problem I have. I purchased a set of SP Performance drilled and slotted rotors for my '87 and they are crap!

I noticed before installing them that there were spots on the hub that the lathe tool cut some durimng the machining process and spots that were still rough cast. I'm not talking about the part of the rotor the brake pads run on or the surface that the wheel mounts to but the area between the two. That's the rotor hub.

Right now my car is at Accurate Wheel and Alignment in Orange, CA. They have an excellent reputation for doing a good job. But they can't fix the problem because they balance the tire and wheel off the car like most shops. No matter how well the tires are balanced, if the rotor is out, it's as bad as if the tire was out-of-balance. It's still a rotating part and spins as fast as the tire. Although not big in diameter compared to the tire, it's made of heavy iron and/or steel, not aluminum and rubber.

The reason I mention this is one, to dispell the notion that a rotor that causes a vibration has to be felt during braking. That's just not so.

Two, stay away from SP Performance rotors. I have sent emails to the on-line store where I bought them and to SP Performance complaining that they are out-of-balance and they are rust magnets having no paint on them at all. These things turn bright red/orange after a rain. Neither the on-line store or SP Performance sent any response to my emails.

And lastly, tell you how I'm going to fix the problem, hopefully.
I may be wasting money but Harbor Freight has a bubble tire balancer on sale for $49.95. It's made for balancing the tire and wheel as an assembly. But I feel if the rotor is out-of-balance enough to cause the front end to shake, it could be used to balance the rotors as well. And I know where to put the balancing clips in the rotors.

Before someone says, "Find a shop that still does on-the-car balancing", I thought of that. But every time the tire comes off if it's not put back on in the exact same position, it will be out-of-balance again.

I'm going to do this anyway. If nothing but for a learning experience. It's only $50.00. I will keep the forum members posted of the results.


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Old 03-19-2005, 01:37 AM   #2
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Jim, I put 'match marks' on my tires and rotors AND hubs. So when I take them apart, they can be put back together exactly as they came apart.
I use a small bottle of touch up paint to put a little red dot on the parts. Just a small dot almost not noticeable by anyone but me.

I also mark the location and weight of the individual wheel weights with one of those little label makers. If it throws a weight I can go and get one and replace it with no big hassle of taking the car in for a rebalance.

The reason for this is I've had a lot of aggravation in the past getting wheels/tires balanced correctly.
When I finally got a set that worked correctly, I matched marked the wheel/rotor/hub.

The Hunter GSP-9700 ? is the ONLY machine to even consider when getting balance done. Unless you can find one of those on the car balancers. IMHO those are good to solve the problem of out of balance rotors.... then just keep everything matched up .... until you want to rotate your tires then you'd need to start all over again....

Actually all my methods/madness are devised to keep me from having to depend on someone else to do things to my Vette that invariably turn out wrong. (and run my blood pressure up)

Good luck with getting your's right.
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Old 03-19-2005, 01:38 PM   #3
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Your absolutely correct.

Every reputable brake rotor manufacturer has this kind of tool in their line or something similiar: or

On a rotor if you look carefully you can see the machining done to balance the rotor. Drilled holes, machined grooves, dimples or a straight edge cut at the edge of the rotors.

Some time weights are used, but milling is far more common.

If a rotor is not balanced from the factory, I would question everything about that rotors quality and dependablity.
While there are only a few very large manufacturers that supply most of the rotors on the market, both OE and aftermarket. There are some smaller operator that either make the high-end stuff or the real cheap stuff.

I would return and buy new rotors.

Last edited by Mighty-Mouse; 03-19-2005 at 01:44 PM.
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