Cause of Rotor Runout

[Thomas H.]

Working on a 66 front end. Has original hubs (assuming) which have been separated from the rotors - for how long I have no idea. At some point they had been painted black which I glass beaded off. The hub surface is clean and flat. Threaded rivet holes in hub and attached new rotors with flat head bolts after countersinking so bolt heads are sub flush to the face of the rotor.

Checking drivers side, runout is 0.002 max. Pass side it is coming in at 0.015" max. I swapped rotors between hubs and got the same results so the issue is in the hub - or spindle? I have not tried swapping hubs between spindles - yet. 0.015" seems excessive to me, could it be the spindle or the bearing races in the hub?

Best method to rectify? Turn on a brake lathe? I have access to one maybe just kiss the rotor to clean it up, but if there is something wrong with the hub bearings or the spindle itself, that would just be masking a different problem?

Suggestions welcome

Thanks,
Tom

[Tom E.]

https://www.summitracing.com/parts/agb-ba90403?seid=srese1&gclid=EAIaIQobChMIgbObhZbm9gIVqdSzCh3bCANgEAQYASABEgKVs_D_BwE

[Thomas H.]

Re: Cause of Rotor Runout

I had the same problem when I restored my 67. I used brake a brake rotor shim to correct. You can order different thickness and once you find the high spot you install the shim between the rotor and hub. Mine have been on there for about 800 miles with no issue. I had planned on pulling them and sending to Baire’s Corvette this winter to have them machine rotor to hub but never got to it.

https://www.summitracing.com/parts/a...SABEgKVs_D_BwE

Thanks Tom.

I had seen them advertised and looks like they would work well for small amount of run out, 00.003, 0.006, 0.009. Bu I'm dealing with 0.015 so I think I need to address that as best I can then take up any remaining slack with a shim as you suggest.

Tom

[Thomas H.]

Re: Cause of Rotor Runout

Swapped rotor / hub assy side to side and runout follows the assembly. So not a spindle issue problem is in the hub. Could replacing the bearings / races help get me down to the point where I can use a small shim?

Tom

[Tom E.]

Re: Cause of Rotor Runout

Tom,
That’s certainly possible although I would think that much runout in a bearing would cause it to fail prematurely. Also possible the race is not seated evenly or the race cup was machined out of tolerance. There are lot of possible faults and/or combination of faulty tolerances which is why the factory probably decided to machine the hub.

[Thomas H.]

[Tom E.]

Re: Cause of Rotor Runout

Tom,
Sounds like you have it figured out. If you lived closer you could use my lathe!
Tom

Edit
Assuming you can figure out how to mount the hub true in the lathe. I suspect the shops that do this have a jig they use.

[Richard M.]

Re: Cause of Rotor Runout

Tom,

John Hinckley told us years ago GM turned rotors and hubs as a assembly.

I did the same on all fronts I ever did using new rotors. I've had up to 0.020" runout on new USA rotors, but it was the hubs not the rotor as the intolerance.

My brake shop was able to turn them as assemblies with a adapter.

Edit. If you attempt to turn the hub face, best to use a adapter to capture the bearings like the spindle does.

Rich

[Thomas H.]

Re: Cause of Rotor Runout

Tom,

John Hinckley told us years ago GM turned rotors and hubs as a assembly.

I did the same on all fronts I ever did using new rotors. I've had up to 0.020" runout on new USA rotors, but it was the hubs not the rotor as the intolerance.

My brake shop was able to turn them as assemblies with a adapter.

Edit. If you attempt to turn the hub face, best to use a adapter to capture the bearings like the spindle does.

Rich

Hi Rich,

I was trying to correct it at the source (or get it close enough to use a thin shim). Since both new rotors I have are in good shape and the source is the hub face, I was looking at making the correction there. Thought we would be able to chck it up on our lathe at work but that is not going to be possible and we would need to make adapters as you point out.

Soooooo.... I have a friend with a brake lathe and I'll have him fix it at the rotor level.

Just another bump in the reassembly road...........

On a side note, the 427 for this car was bought assembled and never fired. "Customer" wanted me to take a peek inside before putting it on the frame - good thing I did. It was just thrown together, probably would not have lasted through break in. I'll spare everybody the details.

Took it to my local machinist (one man shop) a couple weeks back, calls me last week says he has a health problem and can't lift anything for a couple months. So I go to machinist #2 who I've used several times in the past. Dropped block and heads off on Saturday, tells me he won't be able to even look at them for 6 to 8 weeks! He usually has 4 guys in the shop but since pandemic it is down to just him - can't get anyone qualified to work!

Having fun!

Tom

[Mark F.]

Re: Cause of Rotor Runout

...Took it to my local machinist (one man shop) a couple weeks back, calls me last week says he has a health problem and can't lift anything for a couple months. So I go to machinist #2 who I've used several times in the past. Dropped block and heads off on Saturday, tells me he won't be able to even look at them for 6 to 8 weeks! He usually has 4 guys in the shop but since pandemic it is down to just him - can't get anyone qualified to work! Having fun! Tom

No kiddin', Tom - it's serious...and unfortunately, I think getting worse.

I have used the same mechanic for my "regular vehicles" for 30+ years. His wife runs the "office", scheduling, paperwork, etc. and his son has also worked with him for 20+ years. Good folks who "fix" things - not just unbolt and replace. They used to have 3 to 5 people, but they have all faded away.

Recently, he told me he got what he thought was a good prospect mechanic and hired him.
The guy started on a Monday and at the end of that day he asked, "Can I have 2 weeks off - I have to go to prison?"
WHAT??? true story, I kid you not - but what a minute - who knows they have to go to prison for 2 weeks in advance and then come back?

How can a small business function like that? Unbelievable!