jcnst1

I've got a caliper rebuild project going on and decided it would also be a good idea to update to new rotors. Current rotors measure, on average, 1.220 - 1.225' thickness which is above the minimum threshold (1.215") but not by a lot. I put the new rotors on and am measuring fifteen thousands runout (on a dial indicator measuring in 0.001, it runs from 0 to 15 on the dial). I put my old rotors back on and am measuring six thousandths (0.006) runout, much closer to the target not to exceed of 0.005. I have a feeling if I really cleaned up the inside of the rotors and scrubbed the hub with a brass brush, runout would be at or below the runout requirement.

My question is should I go with my old rotors knowing they're within spec but pretty close to the minimum (and return the new rotors to save me some money ), or with the new rotors and shim them to get the runout in spec? Currently the runout of fifteen thousandths with the new rotors seems pretty high, and I'm not even sure if there's a thick enough shim to bring in spec.

ignatz

That is too much runout. I'm at 0.001 everywhere from a set I got from TireRack. They were also cryo'd.

From what you've said so far, I would send them back...... but, are they all that way? Have you tried clocking them... that being a bit of a pain?

Since your old rotors are within spec and if they don't have a rim around the edge, I would stick with them. You do want to remove any glaze. My originals lasted nearly 30 years and I could probably still put them back on the car, although they are at the minimums.

One last thing I've got to say is I've deglazed my originals by gluing emery cloth to a set of old pads and carefully and slowly driven around.

jcnst1

Thanks! By clocking I assume you mean rotating them around and checking runout at different positions? If so, yes, I rotated the front rotor in three different positions and found approx. fifteen thousandths at each position. When I put the old rotor back on in the original position, six thousandths right away, so I think this validates it's the new rotor and not the hub.

67:72

Out of curiosity, what is the thickness on the new rotors?
I'd lean toward keeping the old and clocking/shimming to minimize as much as possible.

shoptek

Good find jcnst1 !!

It would stink to assume the new one's would be in spec, only to create a new issue.

NOT TO HIJACK---What is the best way to you are all using to check runout on the rears? Disconnecting the 1/2 shafts? Is there an alternative method?

jcnst1

The new one's measure at 1.25" thickness. My only hesitation with my originals is the 1.220 - 1.225" average measurement is getting close to the minimum, but given how infrequently I drive it (less than a thousand miles a year, probably more like 500) I'm not sure they'll ever see the minimum?

jcnst1

Good question....I haven't even attempted the rear's yet because I'm currently rebuilding the brake shoes and parking brake (and waiting on some final components)......

jcnst1

Just curious, did you get to 0.001 with shims or without?

GTR1999

For a street car I use NAPA premium rotors. They are fine and you can find them at any NAPA store instead of shipping them.

015" is way too much, I don't even like 005" and can get them dialed in under 003". You have to deburr the mating parts, wire brush won't work. You can shim them without a problem, I would not turn a chip on them. I bolt them on and it works great.

69L88

I used the Raybestos shims BA80303, BA80306 or BA80309 and got all down to less than 0.002. I did drill out the rivets holding the rotors to the hubs, carefully detailing the mating surfaces while preserving the original positions to avoid clocking but actually did clock one front assembly by one lug and got that one down to 0.001.

ignatz

No shims. New bearings everywhere and my mechanic set up the T/A's with new Tom's axles. He (the mechanic) had a very bad case of OCD, but unfortunately has retired. The rotors are nearly perfect, best I could tell. I've had nothing pumped into the calipers over some seven years now. The calipers were new Wilwoods. All good stuff!

Richard454

Disconnecting the halfshafts is the way to go.

FYI- the rear trailing arms- rotors were turned as an assembly when new. That's why they are originally riveted in place.

So anytime you take the old ones off- if you turn them- they will be out of round.

Old rotors that have been turned - or new rotors will have to be shimmed just about every time.

Just take your time-and you can get them really close to.001

Richard

67:72

I tend to agree with you about the life left in your current rotors; that would be a lot of years at 1,000 per. Be aware that the rear disks can only go on one way. Clocking these two won't work if you expect to be able to adjust the parking brake shoes.

Side question for an experienced mechanic: If 1.215" is the minimum thickness for a resurfaced rotor, how much more wear can the rotor safely accommodate?

jcnst1

Good point on the rear rotors. Just waiting on my new rear cable parking brake spring and look forward to making the adjustments so I can get the rotors, re-built calipers, hoses and tires back on.

Haggisbash

Thought: if both rear wheels are off the ground you should be able to turn the rotor on the side you are checking to verify the runout. If you have a helper you could leave the wheel on one side and get them to rotate this while you check the runout on the other side. I haven't tried this but I would before I went to the trouble of disconnecting the half shafts

L-46man

Go with the old rotors....that much run-out will cause the seals to leak.