What it seems like you are talking about is runout measured with a dial indicator. When you say the rotor is true, are you saying there is no runout (wobble) when the rotor is secured to the hub and rotated, measuring with a dial indicator? If this is the case , I would run it. If you are saying it is true by measuring with a straight edge or something then your runout will likely  be more when the rotor is bolted up to the hub. There  are tolerances for rotor runout which are more than .003 but cant remember the maximum.

I would certainly not be happy with 5 thou at the rotor, that runout  increases exponentially when you get out to the tread on the tire.
 It might be a big pain, butt (TS) If it were mine I would pop out the studs and set the rotor up  in  a lathe and clean it up to zero runout.
 As a retired tool and die maker I get anal to go beyond the steps an average "Joe Blow" would to getter  perfect!

Last edited by Rudi (3/28/2016 12:29 PM)

Rudi wrote:

I would certainly not be happy with 5 thou at the rotor, that runout  increases exponentially when you get out to the tread on the tire.
 It might be a big pain, butt (TS) If it were mine I would pop out the studs and set the rotor up  in  a lathe and clean it up to zero runout.
 As a retired tool and die maker I get anal to go beyond the steps an average "Joe Blow" would to getter  perfect!

 
 This might be your best option if your races are seated properly. I had considerable runout on one of my hubs so I bought a new reproduction hub. The new hub had runout that had to be addressed. I would mark the high and low points with a shapie and the amounts so when it gets checked up in the lathe it is in the same position. There is only about 7/16 area in the rear of the hub to chuck it up, could be easy to get chucked up crooked.

DBROWN wrote:

Rudi wrote:

I would certainly not be happy with 5 thou at the rotor, that runout  increases exponentially when you get out to the tread on the tire.
 It might be a big pain, butt (TS) If it were mine I would pop out the studs and set the rotor up  in  a lathe and clean it up to zero runout.
 As a retired tool and die maker I get anal to go beyond the steps an average "Joe Blow" would to getter  perfect!

 
 This might be your best option if your races are seated properly. I had considerable runout on one of my hubs so I bought a new reproduction hub. The new hub had runout that had to be addressed. I would mark the high and low points with a shapie and the amounts so when it gets checked up in the lathe it is in the same position. There is only about 7/16 area in the rear of the hub to chuck it up, could be easy to get chucked up crooked.

The only correct way of truing the hubs on a lathe would be to use a between the centers, conical arbour that seats into the two opposite outer bearing races. This method would duplicate how the hub spins on the spindle.

Thanks Steve. I'll double check those as well.

I found this searching for solutions to runout problems on my front disc brake conversion.  A little late to the party but, what I found may help someone else.

The problem for me turned out to be that the lug studs were a few thousandths bigger in diameter than the lug bolt holes in the rotor.  It wasn't obvious though, because the studs are tapered at the thread end and it appeared that there was clearance between the hole and the stud.

I spent a very long time figuring this out, but after I finally determined the OD of the hub was smaller than the ID of the rotor, there was only one other possible interference.  I used an old set of dividers to measure the ID of the rotor.

I went to NAPA and bought the right size drill and opened up the holes a few thousandths and the runout was gone.