Brake pulsing - do you measure run out ?

[j-dawg]

Using the wheel bolts to center the rotor might work ... I don't know. I'd use them all though. Putting in just 2 and torqueing to spec is likely to warp the rotor which is what I'm trying to avoid. They may be too long and I won't find out until the car is up off the ground and the wheels are off and I can't get to the store to try something else.

No need to torque them. The cone on the bolt will center them on the bolt pattern, and then you tighten the locating pin. Finger-tight will achieve the aim.

[abscate]

I don't think I've ever seen rotors warped by overtorquing. It's commonly reported , but usually not root cause.

[98v70dad]

I don't think I've ever seen rotors warped by overtorquing. It's commonly reported , but usually not root cause.

What is the root cause ... the point of my post.

[scot850]

If you go back to my first post you will see what I believe are the main issues of 'warped' rotors.

If the 'warp' issues happens soon after install, then either faulty discs, poor installation (E.g. the hub face was not cleaned off properly), heavy use of the brake peddle before the brakes have bedded in, or faulty calipers.

If the warping happens (as it would appear in your cases) well after installing it may well be the rust getting between the hub and the rear of the rotor and swelling the face of the rotor so when the wheel is removed and refitted it does not fit correctly, or possibly the brakes are overheating (caliper sticking, or sticking brake pads).

Like abscate, I do not believe torqueing the wheel is the issue. You are more likely to damage the wheel by over-tightening than damaging the rotors.

Have you checked the condition of the rear of the rims where they mate with the rotor? I have found some of mine are heavily corroded by salt and carefully clean them using abrasives to get then back to flat.

Neil.

[98v70dad]

If you go back to my first post you will see what I believe are the main issues of 'warped' rotors.

If the 'warp' issues happens soon after install, then either faulty discs, poor installation (E.g. the hub face was not cleaned off properly), heavy use of the brake peddle before the brakes have bedded in, or faulty calipers.

If the warping happens (as it would appear in your cases) well after installing it may well be the rust getting between the hub and the rear of the rotor and swelling the face of the rotor so when the wheel is removed and refitted it does not fit correctly, or possibly the brakes are overheating (caliper sticking, or sticking brake pads).

Like abscate, I do not believe torqueing the wheel is the issue. You are more likely to damage the wheel by over-tightening than damaging the rotors.

Have you checked the condition of the rear of the rims where they mate with the rotor? I have found some of mine are heavily corroded by salt and carefully clean them using abrasives to get then back to flat.

Neil.

Neil,

I am from "up North". I went to college not far from Canada and my hometown is in the Buffalo snow belt". I'm used to having 2 feet of snow on the ground all winter long. Every college hockey game started with the star spangled banner and Oh Canada since half the team was from Canada (RPI US national champions 1985). So, I've owned many cars with rust issues. But I live in Atlanta, GA now and we get snow about once every three years and it usually lasts one day at most. Salt is used on the roads once every 3-5 years for one or two days. Rust and corrosion is not an issue here. I doubt that its the root cause of my problem. I've inspected every rotor I've removed over the years here and they have a light rust bloom on them. Something like you could get overnight on unprotected metal up north.

[Teddy1975]

Rust and corrosion is not an issue here.

I want to move to there!

I'm about to start on a DIY project with removing rust on lower side fenders and the entire lower portion of my boot lid. Well, "removing rust" in this case is more like cutting off steel and welding new in.

[scot850]

I hear you, having only been to the US couth a few times I don't know the weather there in winter, other than it did snow in North Carolina when was there, but come to think of it, I also got snow and ice when in California on a visit in December one time!

Well, you can probably remove the rust growth issue, unless high humidity gives a rust issue!

Neil.

[johngxc]

Bummer that the original question is still unanswered:

How do you properly (tightly) mount a new rotor to measure runout when installing it on a car with lug bolts that are too long to fully tighten?

For my car (Volvo V70XC) it appears the lug bolts are too long to fully tighten the rotor to hub. So how do you tighten the rotor onto the hub to ensure it's torqued to spec before measuring runout? Are there conical washers available (where?), could you slide a short section of pipe onto the lug bolts with a large washer, or something else? To avoid damaging the lug bolts, anything over the bolts would presumably need to be softer than the bolt, or beveled to match the bolt. And I imagine that putting a pipe or other spacer over the bolt would make the applied torque measurement inaccurate.

To be clear, I'm not asking about dial indicators or indicator mounts, causes of runout, cleaning surfaces, etc. I removed tires and measured runout of rotors that were mounted and will need hammering to loosen. Runout on one side was ~ 0.030 and the other ~ 0.008 (yes, I have a brake pulse issue!). I didn't measure runout when they were new, but I carefully cleaned all surfaces and coated with a thin layer of anti-seize and the pulsing has now arisen twice (first ~ 30,000 miles. Rotors turned, then ~10,000 mi later). I know runout can be from the rotor, axle surface, worn bearings, or something else - I'm not asking about causes, only how to measure runout.

So I'm still wondering how to measure runout when mounting a _new_ rotor, or the old one (to attempt to index it) after breaking it loose. I'd prefer advice from someone that's done this or knows from experience how it's properly done.