Brake Rotor Shims - What are they for? How do they work?
 

How exactly do these work and what are they for? Are they for centering the rotor up between the pads or something? How can they fix runout if they are the same thickness all the way around?

Looks to me they would help if you have un-even wear on opposite side of the rotor like in single piston caliper setups.

Do you mean "uneven" as in more thickness on the non-piston side than on the piston side of the rotor? If so, then ooooooooohhhhhhh. That could be a very beneficial use for them. I could see how they would fix that. But the runout that the item description says those things are supposed to correct? I don't see how they could.

http://www.brakealign.com/pages/diagram.htm

The rotor shims are tapered in 0.003", or 0.006" increments.
You measure the high spot of hub/rotor and put low spot of shim 180 degrees opposite.

Work great I've had a set of 0.003" on my Q45 for 6 years and with precise work I can achieve 0.0005" trueness at the rotor edge.

Wow. That's cool. I suppose they still require the use of electronic equipment, though, right? To spot the highest runout? Or could I just spin the tire and listen for when I hear the rubbing and stop the tire right there then just slap the thickest point on the shim 180 degrees from the center of the caliper/pads? I think that's what I'd do. Be one with my car and have it speak to me. Who needs expensive equipment?

You use a special $52 clamp on dial caliper built for purpose. Just one of the $30,000 in tools a master technican purchases.

Study your FSM to see how process works.

95% of brake jobs don't include runout testing because it adds 1/2 hour per rotor plus time to correct say $80-$100 per rotor.
Depends on the level of perfection owner is willing to pay to achieve

Well, if you're in Marietta, how about I come and borrow your gauge?? Just kidding.

I've seen one of those things before, though. I just thought, as expensive as stuff at the dealer is, it was a machine similar to the machines that spin your tires, except that it hooks to the hub of the car and spins it and measured with a laser or something. :D

Q45tech, how often do you find that you use rotor shims when working with the brakes on cars? I just had my rotors machined for friggin 30 bux and the shimmy is still there. It's a little less pronounced, but still there. I knew it was gonna still be there when I spun the wheel while I had it jacked up and I could hear the rubbing on and off as the tire spun. I can't believe this. Whenever I got my rotors resurfaced or bought new rotors for my 97 maxima, the car braked as smooth as butter. I guess I'll be trying out these shims. I'm so disappointed, though. You think Autozone rents out or loans out the runout dial gauge? Well, I suppose I will check that now. Maybe NAPA does. I'll ask them first since that's probably where I'm gonna buy the shims.

I use them on my cars [1990 Q45 with 321,000 miles, 1994 300zx, 1999 MB AMG C43*] as people won't pay for professional precision.
It takes me 45 minutes of real time to setting up and resetting the dial gauge [you must use washers to simulate wheel thichness and torque 5 lugnuts precisely] deciding what to do.

*The special AMG rotors cost $288 wholesale each for front and I use PowerStop rotors on Q45 and 300zx.

Well, I just noticed on NAPA's website that the Ultra Premium rotors have a maximum lateral runout of 0.002 inches and come with and out of the box "no-turn gurarantee, while the Premiums have a max of 0.004 inches. The Ultras are "Precision Machined For Smooth Brake Operation." The Premiums are "Designed To Improve Stopping Distances Minimize Brake Fade & Extend Pad & Rotor Life."

Looks like I just bought the cheaper ones and they suck. I would think that getting them turned at PepBoys would eliminated the runout, though. I already ordered that gauge off Amazon, though. So I think I'm committed to getting the shims. Even if I hadn't bought the tool, I couldn't see myself throwing away two rotors that stop fine, even though I hate the shudder.

So Qtech, I got a gauge and measured and from the lowest to highest point on my rotors is like 0.012 and like 0.013 inches on the right and left, respectively. So which shim would I get? The 0.009's? The NAPA shims descriptions say that the 0.003 corrects 0.003 inches of runout and the 0.006 and 0.009 say the same things respectively. So does that mean that the thickness difference from the thinnest side to the thickest side of a 0.003 inch shim is 0.003 inches? That would mean that the 0.009 won't even totally correct the runout on my rotors. I can't believe that after getting the rotors cut at Pep Boys that there was still at least 0.012 inches of runout in both rotors. How can this be? (I'm still smarting over the fact that I bought new rotors six months ago and ever since I replaced them, the shudder has been about as bad as it was before I got replaced them.)

Sigh. Anyway, should I go ahead and get the 0.009's? That's what I think I'm gonna do by the end of today unless you say otherwise.

The hubs should be measured and ground to perfection say 0.0005" as the radius gets multiplied out to rotor edge.
If a perfect rotor is mounted on a dirty corrosed rusty hub the rotor takes on the multiplied error.

Study FSM which shows how hub must first be perfect!

You can stack different shims as the rotors will change as they temperature cycle and bend.

Did you use washers and torque lug nuts PRECISELY on rotor prior to measurements.
Try turning rotor position on hub = different positions possible with 5 lugs to find the minimal run out position.

See why this can take hours per rotor to find the minimal spot then fix the minimal with correct shim. Then check them 30 days later and record changes as the rotor settles in.

Meeting OEM SPECS requires lots of paid work and time.

Well, I didn't torque with a torque wrench and I only used two (well-tightned) lug nuts and washers, but I turned the rotor one lug and the high and low runout spots were at the same points. I concluded that the torque and using only two lug nuts contributed only minimally to inaccuracy if any, since the runout was at the same spots I'd marked. I also so in the brake manual that it said using two lug nuts was sufficient. I thought I saw that, anyway. I'm taking the car to my Nissan tech friend Friday. He's doubtful about Pep Boys' resurfacing.

And tell me, who's hubs are not rusty? How do I 'grind the hubs to perfection?" Do I take them off and sand them?

Everytime I replace my pads I polish my hubs [on the car] to remove corrosion and rust.

Maintaining as new specifications means systems must be [look] as brand new.

Dont forget that wheel inside mounting surfaces must be clean.

TWO LUGNUTS is not enough use all 5 if you want perfection.

Most chain store shops are concerned with speed of production not accuracy. Since less than 1 in 10,000 are actually measured for runout.


Remember Nissan max runout specs are 0.0028" and 0.001" is better since it leaves some room for changes as the rotor cycles and ages.

Well, I took the car to Nissan yesterday and I paid $108 to have two friggin rotors machined and I'm still, yes, still getting vibration. It's a different patter, but it's still there. I'm so ticked off. I'm going back Monday to see what they say. But I think I just paid $108 for nothing. I'm thinking now that these rotors must just be garbage. I don't know what to think, but if Nissan says that they cannot do anything, I'm just gonna ride this things out probably until I buy new pads. And I'll get either the semi-metallic or cheapo metallic pads and use them.