Rotor Run out
Thread Starter
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Rotor Run out
I just got my motor back together and I was so happy that I've really been running it hard. So my front brakes developed a shimmy and pulling to right. I had my buddy at the race shop surface the rotors and they were only slightly out and cleaned up in just one pass.
But anyway this is how you can do the fronts. I clamped a metal block to the upper spindle to get a flat area for my magnetic base to attach to. I ended up putting .008 of metal shim on the passenger side. It is not difficult with a nice dial indicator.
You can also see that my home made air dam under the radiator is nearly on the ground when I turn down the coil overs.
But anyway this is how you can do the fronts. I clamped a metal block to the upper spindle to get a flat area for my magnetic base to attach to. I ended up putting .008 of metal shim on the passenger side. It is not difficult with a nice dial indicator.
You can also see that my home made air dam under the radiator is nearly on the ground when I turn down the coil overs.
Thread Starter
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Thread Starter
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Rotor run out is something that I rarely do. So each time is a good refresher course. Things that I had to relearn were
1. Your c2 or c3 spindle wheel stud surface can have run out. So can the rotors. So when you first mount the rotor and mark it's lowest point. Take it back off and rotate it 180 degrees. This should take out some of the run out.
2. Distance from stud surface to the outer rotor diameter . Say that from low point to highest point is. 0.008 out. You only need to shim say. 003 to bring the run out to less than two thousandth. Without thinking mine was like. 012 out. So I put in a. 012 shim. Then I went to all screwed up with a different low point.
3. Over time your wheel bearings are going to ware Before attempting to fix the rotor run out you should inspect and regrease the outer wheel bearings and set the correct bearing clearance. Slop in the bearings will lead to inconsistent dial indicator readings.
1. Your c2 or c3 spindle wheel stud surface can have run out. So can the rotors. So when you first mount the rotor and mark it's lowest point. Take it back off and rotate it 180 degrees. This should take out some of the run out.
2. Distance from stud surface to the outer rotor diameter . Say that from low point to highest point is. 0.008 out. You only need to shim say. 003 to bring the run out to less than two thousandth. Without thinking mine was like. 012 out. So I put in a. 012 shim. Then I went to all screwed up with a different low point.
3. Over time your wheel bearings are going to ware Before attempting to fix the rotor run out you should inspect and regrease the outer wheel bearings and set the correct bearing clearance. Slop in the bearings will lead to inconsistent dial indicator readings.
Race Director
Joined: Apr 2009
Posts: 19,294
Likes: 2,753
From: Charlotte NC
Agreed. When I index the rotors I use a shim that I make that is HALF the thickness of the TOTAL run out....or as close as I can get to it. I use steel shims stock that comes in thousandths and I can get them just about perfect.
YES...making sure your bearings are set correctly is the MOST important first step.
And whether it matters or not I install all five wheel nuts and torque them so I am dealing with the assembly being on the hub as it would be when it is on the ground going down the street.
Why do I do it that way some may ask. Well I know it is not the same but the principle of assembly is still the same. A long time ago I would use only two bolts to hold a door on when I was creating the door gaps and making sure the door was flush. When I installed all of the bolts and tightened them...what I worked hard to get correct was throw off by how the added bots tweaked the assembly just enough to cause me to go in and have to correct things. So...I now take no chances and use all fasteners when I reassemble something for fitting and adjusting. Since I have employed this practice. I have no surprises that show up later.
DUB
YES...making sure your bearings are set correctly is the MOST important first step.
And whether it matters or not I install all five wheel nuts and torque them so I am dealing with the assembly being on the hub as it would be when it is on the ground going down the street.
Why do I do it that way some may ask. Well I know it is not the same but the principle of assembly is still the same. A long time ago I would use only two bolts to hold a door on when I was creating the door gaps and making sure the door was flush. When I installed all of the bolts and tightened them...what I worked hard to get correct was throw off by how the added bots tweaked the assembly just enough to cause me to go in and have to correct things. So...I now take no chances and use all fasteners when I reassemble something for fitting and adjusting. Since I have employed this practice. I have no surprises that show up later.
DUB
Thread Starter
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
The Half shim width is a great formula 
my example of .008 runout and. 003 shim is just close to the half idea and probably more correct for my larger diameter rotors.
my example of .008 runout and. 003 shim is just close to the half idea and probably more correct for my larger diameter rotors.
Last edited by gkull; Nov 3, 2018 at 11:10 AM.
