got to balance rotors?

[Doug Steinel]

put new front rotors on my '77 a couple of weeks ago. I notice at highways speeds I have developed shaking in the steering wheel. Could the new rotors have upset the balance in my front wheels, or is the shaking coincidental and probably due to the need to balance the front tires? Does one merely bolt on the rotors or is balance an issue that must be dealt with?

Doug

[Oh Haha]

I would suspect your wheels bearings. Are they tight? Did you replace them or just repack?

[Doug Steinel]

I repacked them and they are tight. With the car jacked up, there is little play in the wheels.

[Gunter]

Doug:
New rotors are checked for axial, and radial play.
I always put a dial indicator on because I want to know.
They should be within a few thousands ".
If not, the cause could be dirt/burrs between hub and rotors or distorted hubs.
Try a dial indicator on the rotors.

[Dixie]

You do not need to balance rotors. First, the small amount of mass they present does not extend far from the axle. Second, most rotors are balanced when they are manufactured. None of this absolves your new rotors form being the problem. All you know at this point is the problem was induced by changing the rotors.

I'd start with the easiest stuff to do. First, I’d recheck how tight the bearings are. How much effort does it take to slide the washer behind the nut holding the bearing in? Tension on the washer is the easiest way to gauge how tight they are. There should be no discernable wiggle at the road wheel. If that checks out, I'd put the old rotors back on. If the problem goes away, you know it's the new rotors.
.

[Gunter]

Play in the bearings has no effect on balance.
If the bearings are worn/burned, you'll feel vibration.
If tires/wheels are balanced, and there is no distortion in the hubs, you shouldn't feel any vibration.
I have seen more than 0.005" axial play on rotors due to distortion.
The maximum recommended is 0.003".
Try a dial indicator and check it out.
Normally, rotors do not require balancing.

[oneblueyedog]

Old tires? Directional tires accidentally switched?

[Quicksilver]

You shouldn't have to balance a rotor but it is possible. If you look around the outside of the rotor you will see one or two spots where it has been machined for balance at the factory. It is extremely uncommon but I have heard of them screwing it up.

I think it is much more likely that it is the wheel balance being off.
Another idea is: The wheel and the rotor's balance is never perfect. They are just within a reasonable tolerance. If their remaining inbalance happens to line up with each other it might be noticeable. Try remounting the wheels on the rotor turned 2/5ths of the way around to see if it calms it down.