Run-out on new brake rotors Topic is solved

[FireFox31]

My new Zimmermann rotor shows 12/1000" run-out when installed yet each individual component has acceptable run-out. What am I missing? What tool can I use to smooth out rust on wheel hubs?

I check run-out using a quality Mitutoyo dial indicator on a Noga magnetic holder. I mounted the new front rotor on a machine shop lathe, set the indicator, and spun the rotor slowly by hand. Inner and outer faces showed 3/1000" and 4/1000" run-out.

I set the dial indicator on the wheel hub but it was too rocky with rust to show a clean run-out. I sanded the hub face with an 80 grit air powered tool. I was gentle but it was still aggressive. Once the inner and outer ridges were rust free, the dial indicator measured no run-out on either.

I put a tiny bit of anti-seize on the inner hat of the rotor. Upon mounting, it felt firm on the rotor with no rocking. Yet, when I measured the run-out, it was 12/1000" between the 12 o'clock and 6 o'clock positions. Before I sanded the hub, it measured 22/1000"!

Rotor has minimal run-out, hub has no run-out, yet together they have bad run-out. I haven't driven on the rotor so it still has the silver coating. This happened on my rear rotors as well, so I drove 1000 miles and they still had 12/1000" run-out. I must be doing something wrong, but I'm checking everything to be sure it's right.

[abscate]

Yeah, your new parts are already at 3x Volvo spec. #sadface

Volvo let’s another 0.005 runout creep in on mounting, from 0.035mm to 0,040 mm, or a total , in Us measurements, 0,0016 inches

With today’s supply chain problems, I would be be thankful you have rotors in hand!

[FireFox31]

They're 3/1000" on the lathe and that might be from the lathe being ancient and not perfectly maintained. And the hub has no run-out. So how could I be introducing 9/1000" run-out when I mount it?

Maybe the anti-seize caught some contamination? But I wiped it all off and tried again. Maybe it's unstable to mount the magnetic dial holder to the strut (but I had it there when measuring the hub).

I only did one side so far. I'll do the other side today and see what happens. I'll revert to scraping the rust off the hub with a razor blade instead of an aggressive sanding pad. I sanded it so much that I half removed the tiny grooves in the two mounting tracks. But I removed a large area of high spots which were 4/1000" off.

[volvolugnut]

Clean up the rust as best you can. If you find any runout on the hub, you can match rotate the hub and rotor to reduce the combined runout. When you bolt up the parts, use care when mounting the parts to assure the bolts are tightened in a cross pattern and there is no warping.
volvolugnut

[FireFox31]

I just worked with the other (left) front rotor and had good results. Before sanding the very rusty hub, the rotor showed 17/1000" run-out. I carefully sanded the hub, frequently checking its run-out. The rotor showed 3/1000" run-out on the lathe and 2/1000" on the clean hub. I hope that's permanent.

I'll try carefully sanding and checking the bad first side (right) again.

This work is for Geronimo, the rusty 350k mile 2000 V70. Slow going, but I'll get its rusty brakes all replaced.

[scot850]

I use a couple of different wire bushes on a drill to clean all the surfaces so they are free of any rust on the surface. With all the different brush heads you can get you can get into any area of the wheel bearing hub face. I never use copper grease between the surfaces as it is too this and difficult to get flat. I use a cloth and WD40 to wipe over the surface before fitting the new rotor.

Strangely, other then Volvo rotors on our XC70, the only brand I had issues with were Zimmerman rotors on my 98 V70XC, and in particular the rears. Making sure the faces of the rotor and the hub are clean prior to installation makes all the difference. I'm not saying Zimmerman are bad, but they are the only ones I had issues with. I have just fitted new 302mm Zimmerman rotors to the front of my 'R' and they are just great. I like the anti rust treatment they use too.

Neil.

[FireFox31]

It's the locator pin. When I check the run out without the locator pin, pushing the rotor hard against the hub, there is zero run-out. When I tighten the locator pin, there is 6/1000 run-out.

The car is using a simple M6 X 1X10 bolt instead of an actual locator pin. It's too short, should be 15 mm. Of course I have used pins at home, but forgot them. Perhaps swapping one on will help.

For now, I'll leave the pin barely tight. Let the wheels, torqued to spec, hold the rotor. I'll see if I feel vibration.