I found while installing brake rotors that by changing the clocking position of the rotor on the hub it changes the measured rotor runout. I used a magnetic base and a dial indicator as an effective way to minimze my rotor runout.

On my '01 F-250 SD here is what I found when installing new ART front rotors...

Left rotor maximum runout was 0.005". Minimum runout 0.003" with optimal clocking of rotor on hub.

Right rotor maximum runout was 0.004". Minimum runout 0.001" with optimal clocking of rotor on hub.

 

Huh? Clocking Position? Rotor runout?

 

Interesting idea, but I'm not sure you'll feel .002 to .003 difference.

 

Rotor runout is how much axial (or lateral) motion of the rotor braking surface as the rotor rotates. In an ideal hub and rotor assembly there would be no runout. With real world mfg, there are slight variations in the surface of the hub and rotor.

Clocking refers to the rotational position of the rotor on the hub. The rotor can be set in 8 different rotational locations on the hub since there are 8 lug studs. You can move the rotor clocking by taking the rotor off the hub and then rotating the rotor relative to the hub and studs and reinstalling the rotor.

 

You shouldn't feel it at all after a brake job. I think the point is to delay the uneven wear to the point you will feel it in your brake pedal.

 

My point was that .002 lateral runout should be imperceptable in a brake system. I'd bet the allowable tolerances on factory rotors and hub assemblies is more than that..but I could be wrong.

 

The Haynes manual specs front brake rotor runout limit at 0.0015". However, that may not match the Ford spec.

 

Eric, you are not wasting your time

Every sealed/unitized hub known to man has a little bit of runout. If the hub is .001", and the rotor is .002" (at the brake surface), you can imagine that overall you'd wind up with .004-.005" or even more total. Which is probably enough to feel.

I went through this with my '96 t-bird and '97 cougar. One of the studs is marked with yellow paint. If you line up the tire valve with that stud, you get no vibrations. If you don't, you get a shimmy about the 40 mph point.

Then, I noticed that the rotors did have some runout, so I ran a dial indicator over the surface of the hub, found the high-spot, put the rotor on, and like you did, found the position where the rotor had the least OVERALL runout.

On the SD, I've never noticed a paint mark on the studs or hub, but I can imagine they DO have some runout, even brand-new. Next time I do the brakes, I'll be certain to get the dial indicator out and do what you're doing

 

Wow....all these years and I didn't know it made a difference when you mated the rotor back to the hub. Now I'll have to pay attention.

Thanks guys.

 

It would be interesting to test a bunch of used and new trucks to see what runout is actually there. I may check my 150 just for grins.

 

What's even more fun is getting a rotor where the back of it is not square with the braking surface

That'll drive you nuts. Shop cuts the rotor to square it, still not square - because they use the FRONT of the rotor to cut it, not the back.

I've learned to, if available, use a dial indicator and always check for runout while you're in there. Unless you're just freshening up the pads or something, but even then, it can't hurt to check.

 

I have also experienced the dissatisfaction of having more rotor runout after the rotor is turned than before.

Equally annoying is finding a replacement rotor that has more runout than the rotor you are replacing.

I always check before and after on all rotor work. I also keep records to see if my rotors get worse over time.

 

Thats why Ford actually tells dealerships to use the on vehicle brake lathe, instead of the old style lathe. Its kind of a pain to use, so, most dealerships dont want to use it. For warranty work, Ford will not pay unless you use it (like the dealership is gonna admit not using it)

 

Interesting... thanks!

 

Does the factory index the rotors when installing them?