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Topic: Front Rotor Run Out

in Forum: C3 Handling Components

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Front Rotor Run Out (1/11)
8/16/09 5:06pm

jp75vette
Former Member
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Bloomfield Hills, MI - USA

Vette(s):
1975 Corvette coupe, 4 speed manual, 383 ci 9.5:1,Edelbrock dual plane Air Gap intake, Alum Heads,Comp Cam, roller Rockers, PS,PB,Tilt

Joined: 6/29/2008
Posts: 199

I am redoing the brakes all around on my vehicle. The first caliper I put on (driver's rear) was right on the money for run out. I next went to the driver's front and it is out by 0.015". I moved the rotor around to differenet stud positions, but the run out stayed at 0.015". I have read about tapered shims, but am having trouble to find a place where I can get them. Does anyone know a good source?

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Front Rotor Run Out (2/11)
8/16/09 6:19pm

crossfire1982
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Cramerton, NC - USA

Vette(s):
black 1982 coupe slate gray interior, 350 crossfire, 1985 fuel pump, Steeroids R&P conversion

Joined: 8/22/2006
Posts: 1094

I was looking for then about a year ago and found them online but I cannot remember the site, it may have been on ebay but they WERE NOT inexpensive. I ended up using .002 stainless steel shim stock to make shims to bring mine true. I drilled and tapped my spindles and bolted the rotors to the spinle flange so things would stay where I put them.

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Front Rotor Run Out (3/11)
8/16/09 10:27pm

Adams' Apple

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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
Posts: 20128

Hobby Shops usually have an assortment of brass stock...you might give that a shot.
Does the actual run-out stay in the same location on the hub, regardless of the rotor position?
Or, does the run-out follow the rotor position?
You may have a bent hub, or possibly some rust that is keeping the rotor from seating properly.

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Joel Adams
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Front Rotor Run Out (4/11)
8/17/09 10:41am

dcherr
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Elkhart, IN - USA

Vette(s):
1975 Red T-Top 1972 Red Convertible

Joined: 10/7/2007
Posts: 209

Whay don't you take the hub and rotor together and take it to a local auto parts store that can turn rotors and have the true them up. WORK GREAT FOR ME.

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Front Rotor Run Out (5/11)
8/17/09 7:12pm

I'm going to do a few more investigation steps and see what the run out is of the hub by it's self. I am wondering if the bearing setup affects the run out?

I'm also going to really remove all rust on the hub and to double check that there are no burrs where the rivets were.

Did you double check the run out before and after you had the hub/rotor combination tured up? My rotors are new and I would like to see if I can fix this without removing material.

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Front Rotor Run Out (6/11)
8/18/09 11:06am

dcherr
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Elkhart, IN - USA

Vette(s):
1975 Red T-Top 1972 Red Convertible

Joined: 10/7/2007
Posts: 209

YES I DID

Yes the bearing set up will affect the run out. I think they need to be set at 12 inch pounds. Or tighten them up and then back them off a 1/4 to 1/2 round till the rotor is free but no in & out play.

I had new calipers, brake lines front & rear, wheel bearings, trailing arms rebuilt & sent the new rotors along to be trued with hub, pads and rotors and still had a pull and surge in the pedal. Took the front hub and rotor and had then turned together. Only took about about 1 to 3k off to true them up. Thumbs Up

No problem now.

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Front Rotor Run Out (7/11)
8/18/09 1:28pm

Adams' Apple

The front rotors should never be removed from the hubs to start with...they really should be kept riveted together, as there's really no need to separate them like there is on the rears. Not that it's a bad thing to do, just that there's no reason to do it. That would keep the possibility of hub/rotor run-out a non-issue....

I have seen hubs that were far enough off to cause a bad run-out issue at the outer edge of the rotors, so it's definitely something to look into.

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Front Rotor Run Out (8/11)
8/18/09 1:34pm

OK, if I have some time tonight, I will start to take some measuerments to see what the root cause is.

Adam, I had to take the rivets on the fronts out as the rotors were too thin and I had to replace them. Should I rivet them back?

When I take the measurements I torque the wheel nuts on backward to keep the rotor tight to the hub.

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Front Rotor Run Out (9/11)
8/18/09 6:06pm

Well I spent some time taking measurements.

The Front Driver hub only side read as follows at each wheel stud;0,+0.003, +0.010, +0.009, +0.003. With the new rotor, the max run out was 0.015.

The Front Passenger hub only side read as follows at each wheel stud;0,+0.001, +0.002, +0.001, 0. With the old rotor, the max run out was 0,+0.007, +0.011, +0.007, 0.

I guess I will look to see where I can get the combination rotor/hub trued up.

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Front Rotor Run Out (10/11)
8/18/09 11:25pm

Adams' Apple

[QUOTE=jp75vette]Adam, I had to take the rivets on the fronts out as the rotors were too thin and I had to replace them. Should I rivet them back? [/QUOTE]

No, no..I'm not suggesting that at all... Smile

The rotor/hub assemblies aren't that much more expensive than just rotors, so if the rotor is trashed, it's just what I would do...replace the whole thing. That's just me, tho...either way is totally acceptable. My point was that it does keep problems like this from occurring.
Riveting the rotors back on will do nothing for the run-out at this point anyway, unless you had them turned as an assembly afterwards.
I always turn new hub/rotors when I get them anyway, just to make sure they are true when installed. It's harder to true a rotor to a hub if it's in two pieces, as most cars are these days.

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Front Rotor Run Out (11/11)
9/24/09 12:49pm

2nd2ja
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Lino Lakes, MN - USA

Vette(s):
71 Coupe LS5 454 Auto

Joined: 1/8/2009
Posts: 138

I too checked the run out on my Vette w/ the brake job i'm doing. While one side was very close, the other side was way off. after turning, it would have been just over the minimum.

I bought new rotors. You don't need to rivet them back on. Even in my factory service manual it lists they don't re-rivet them. However, drilling out the rivets took some time on my dad's milling machine- it was not an easy pop-them out as in most articles (except for the rear seal whicjh does tap in).

My bearings were decent but i figured with all new parts, i might as well change those, too. Another 50+ bucks but the Moog perfromance bearings are piece of mind. Installing them wasn't too hard, but i had to use my dad's press at work.

If i could've bought a whole assembly hug/rotor- that would have saved me some time and work. Corvette Specialities (where i bought most parts) didn't have these. So I ended up learning the hard way.

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