Brake rotor runout- Rookie needs advice

[Greg S.]

I'm in the process of redoing brakes. This is my first experience with discs. I have measured the runout on the rear discs. One side has a difference of .017 from low to high and other has .015. See the attached photo for actual values around the circumference of both discs. Is this an acceptable variance? If not should I shim rotor or have rotors turned? If so, where do you get shims? The rotors are not new but are well over minimum thickness and in good shape.

Second photo is the setup used to measure.

[Patrick H.]

Re: Brake rotor runout- Rookie needs advice

Raybestos makes shims, and sells them through Rock Auto as well as others.
You can Google for "brake disc runout shims" and learn a LOT of information.

Or, you can make your own from stainless or brass material of the correct thickness.

Verify first that it's a problem with runout and not thickness variation, or you'll be improving one side of the disc while making the other side "worse."

http://www.brakeandfrontend.com/roto...nd-correction/

[Gary R.]

Re: Brake rotor runout- Rookie needs advice

Greg,
Your spec's are way out and no good. I set them to under 0025" when I set them up. With that amount I suspect you might have some burrs someplace. Remove the rotors and run your fingernail across the holes inside the rotor hat. Do the same for the spindles or flanges. measure the thickness of the rotors at several points. Then make sure your indicator is tight in the base and the base is tight. Also make sure the indicator isn't sticking. If you want to go over it call me during the day and I'll go over it with your. Typically I see 005-006 as the range when I check rotors and won't use anything over 0025" even thought the spec is 005"

[Jim T.]

Re: Brake rotor runout- Rookie needs advice

Greg I can see in your picture that you are using wheel lug nuts to retain the rotor. Assume you have no rivets retaining the disc to the spindle. If you removed the spindle and rotor and send them to Bairs to have the rivets installed you would not have the runout that contributes to the calipers pumping air and having to bleed the calipers to remove the air and restore rear braking.

[Greg S.]

Re: Brake rotor runout- Rookie needs advice

Had time to remove and clean driver side mating surfaces today. Also backed off parking brake as I had them so tight the wheel was difficult to rotate. Re measured. Big improvement. Delta now .005-6. Will get shims and try to improve. Will do other side tomorrow. I also attached the indicator more solidly. I'm learning.

[Greg S.]

Re: Brake rotor runout- Rookie needs advice

I have looked online and cannot find shims for individual studs. All that comes up is hub rotor shims to correct either .003 or .006 runout. They are pretty pricy at about $16.00 each. Are these the best product to use?

[Gary R.]

Re: Brake rotor runout- Rookie needs advice

I have looked online and cannot find shims for individual studs. All that comes up is hub rotor shims to correct either .003 or .006 runout. They are pretty pricy at about $16.00 each. Are these the best product to use?

Forget trying to find "made" shims, waste of time and money. I use sheet shim stock from 001-015" ranges. You will need a punch set though. a good hardware or industrial supply should have the shims. One on a stud is usually all you're going to need. Those NAPA ones were 1/2 moon shaped and don't work all that good. I prefer shimming over turning a chip in this case.

[Mike E.]

Re: Brake rotor runout- Rookie needs advice

Forget trying to find "made" shims, waste of time and money. I use sheet shim stock from 001-015" ranges. You will need a punch set though. a good hardware or industrial supply should have the shims. One on a stud is usually all you're going to need. Those NAPA ones were 1/2 moon shaped and don't work all that good. I prefer shimming over turning a chip in this case.

+1

I tried the NAPA ones. Waste of money and time. BTW it looks like your spindle is aftermarket. Do you know if the rotor is original? If so that might explain the excessive run out. I replace both spindles and rotors. The runout was well within spec on the rears, didn't need to shim it at all.

Mike

[Greg S.]

Re: Brake rotor runout- Rookie needs advice

Is this the shim you tried?

http://m.napaonline.com/Tablet/parts/PartDetails.aspx?Id=UBPBA80306_0163776875

if not how did you end up shimming the rotor? I looked into buying shim stock and punches to make some but cost was close to $100. Gary, You might be able to make and sell shim kits.

[Mike E.]

Re: Brake rotor runout- Rookie needs advice

Is this the shim you tried?

http://m.napaonline.com/Tablet/parts/PartDetails.aspx?Id=UBPBA80306_0163776875

Yes it was one of those.

Here is the picture of the shims on the front I made using Gary's method. Mine were punched round but that's not necessary.

Curious was the runout measured with the 1/2 shaft connected to the spindle?



Mike

[Gary R.]

Re: Brake rotor runout- Rookie needs advice

Those are fancier then what I cut out. I just sissors them out and punch the ID. Worked great on all the TA's I built so far.

[Mike E.]

Re: Brake rotor runout- Rookie needs advice

Those are fancier then what I cut out. I just sissors them out and punch the ID. Worked great on all the TA's I built so far.

Yep...totally unnecessary...Had a buddy at a tool and die shop with a big punch make them up for me.

Gary....Do you think Greg should pull the outside end of the 1/2 shaft and check the end play on the rear wheel bearing and make sure there are no issues there?

Mike

[Gary R.]

Re: Brake rotor runout- Rookie needs advice

Mike, Greg

You could do that for 2 reasons if you're so inclined.

1- to check the endplay in the diff, with the 1/2 out you can really see what is going on there to know. Not that you want to get into the diff at this time but just as a Preventive measurement.

2- without the shaft or caliper then the bearings play will be easier to check as well. Is that needed, no again just a PM. The bearing spec if 001-008 but if you grab a wheel stud and can see and feel it move in/out you're over 003". That is where I see them move on the bench. As you know the spindle flanges are rough faced and many have 008-012" runout in them and have been like that since new. Others are tighter . Some out there use those numbers to tell customers the spindles are bent and should be replaced. I have no doubt spindle flanges can be bent but that will require a good impact and usually there is some evidence around the wheel well area to support it. I had guys tell me they were sold new spindles and they had full history of their cars without impact. Spindles are not going to warp over time so just beware. I know it's a little off topic but the point should be made.

Again Greg if you want to go over this type of work just let me know.

One more note that may help some of you :I set my bearings up to the point of no lateral play, meaning the magical number of 002" every expert on every forum spec's out means nothing to me. Once I reach 002" endplay in my fixture I can still see movement on the initial loading. Yes it is 002" but it's a false reading. At that point, I know I have already parallel ground the spacer and shim so all are flat against each other so I grind off .0003" to .0004" until I just reach the point where there is no loading. Then I know the there is no lateral play and the endplay ends up in the 0015 range. Interestingly when I setup 31 spline axles with the larger bearings I go to a preload setting completely. I'll be covering all of this in the Carlisle seminar next month for those interested that are attending.

[Gary R.]

Re: Brake rotor runout- Rookie needs advice

This is how I do rotors, front or rear. I wrote this a while ago and haven't gone back to it much but it may help you.

http://www.digitalcorvettes.com/forums/showthread.php?t=77063

[Steve G.]

Re: Brake rotor runout- Rookie needs advice

I wouldn't use individual cutout shims. For one thing, you no longer have the full surface contact of the rotor to the face of the hub. You compromise the strength and heat transfer.

Secondly, you would have a very difficult time establishing the correct gradual transition from the thickest shim to no shim. If your thickest shim is .006 and the thinnest spot is no shim, what should the shims between the two be so that you establish the correct transition and don't distort the rotor when you tighten it?

The tapered shims provide full surface contact and there is no concern about transition, it is established in the taper.

Steve