Inherited a basket case non finished 78 C3 and needs a ton of work. Brakes had been gone through 20 years ago and car never say any miles. I pulled the brakes and pad life was great as to be expected. Front and rear rotor rivets had been drilled out so the rotors were probably turned. Pass front caliper had a small leak on one piston so I pulled them all and rebuilt with SSBinc high heat Oring kit (car will sit 6 months a year). I pulled the rotors and both the fronts were under min spec by .030 so I decided to yank them all and replace. Got the new rotors, new pads and the calipers are ready to go.

Here's what I did to setup the run out test:
- wire brushed the hub
- used nuts on all the wheel studs with washers and Hit them with a small 3/8" impact to get them good and tight.
- attached dial gauge to the Trailing arm and the rotor
- contact to the rotor with the dial tip is like 1/4" from the outside edge of the rotor.
- spin the rotor with small pry bar to try and keep the force applied as close to the center as possible.
- The car is up in the air and the suspension is unloaded.

Decided to check run out on the rear driver first and I'm getting .010" on one end and -.006" directly across from it (so that's a total of .016 run out). 90* out from those 2 (straight across from each other) is .000" or my set point for the dial. I started collecting aluminum cans but I feel that If I put 1 or 2 layers on the -.006" side I can even that out to about .002" (assuming soda can thickness is .004") and that will bring the .010" side down to .002" theoretically. I did wire brush the hub and don't remember seeing anything that would cause it to be up like that. I also tried jacking up the 1 side to get the half shaft more "level" and it didn't seem to affect the readings. I pulled on the rotor 9&3 and 12&6 and saw some play in the bearing but I assume that's normal but around .002-.005" or something. I did end up going with the high temp Oring kit from SSBinc so I should be good to .005"

I watched a few videos on how to do this and just hope I'm not screwing it up. Do the rear wheels need to be jacked up to do this correctly? Do I need to verify bearing run out at the top and side (pulling at 9&3 or 12&6) basically moving the dial gauge up to the top and side for these tests? For the front rotors do I need to pull the bearing dust cap and tighten the bearing for zero slop to do the fronts? Or should I just leave them? I'm spinning the rotors from the lugs with a small pry bar which I thought I read means the bearing doesn't really become and issue and most people don't talk about tightening the front bearing when doing the fronts.

 

I did my fronts. I made sure I tightened up the bearing nut just a bit. I turned the rotor with my hand on the outside edge of the rotor. They should turn easy. I started first by checking the hub runout. Then I installed the rotor. I checked the rotor in all 5 lug positions. I found one position with the least runout. When checking runout, make note of the lowest vs highest point of the runout to get total runout.

 

Checking the hub you just use the dial on the hub and spin it? Whats the point of checking the hub run out? My understanding is that most rotors are ground when NEW really flat so any run out would be directly caused by the hub which is what we are shimming to correct.

 

fyiO
manual says 1 inch from outside edge and less than .005

 

Good to know! I couldn't get my dial gauge any closer to the inside of the rotor so I got it there. I will be picking up a flex arm for that today so I can move it closer and inwards. I also think if I do a .004 shim within 3" (hub) its closer to .006-.008 at the rotor edge if I'm not mistaken.

 

Yes, you check the hub the same way you do the rotors.
New rotors will not be zero runout. I got a set of new rotors, and I had my old rotors turned, they both have runout. I checked the hub runout to get an idea where the best match to the rotors would be.
And besides...... If you check your hubs and they are way out,,, replace them or the bearings. If they are nuts on, you know it is in the rotors.

 

Pick up the farthest point of the rotor and get it under 003" I just did a set of arms with new rotors and axles, with my prep and didn't have to shim them. Runout in both was 001"

 

What is your prep? On the rears the rotor only fits one way so you can't rotate it to help zero it out.