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      10-04-2011, 08:20 AM   #1
BimmerRob08
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APracing disc run-out tolerance

I've posted a few times before about a light wobble/vibration that my M3 has at about 80+mph. With any brake application at those speeds, the vibration in the steering wheel and front end is magnafied from the applied force of braking. Can't feel any feedback in the brake pedal and it's smooth at lower speeds.

I have new ARC-8 wheels, new tires, road force balanced and all checked out by my local BMW dealer for any suspension issues. Also another alignment.

I've noticed that this braking vibration has developed over the last several thousand miles, no track time ever so far.

I at this point believe it's the front disc rotors that must be causing this. The car is on jacks, I've rotated the disc by hand to see if I can feel any rubbing or grabbing of the pads. Both front disc's rotate smoothly as far as I can see. Only the left front wheel bearings seem to spin a bit tighter than the front right axis.

does anyone have any run-out tolerance data for AP? The dealership said they can measure it out and see if there is a warpage going on that can't be seen. I'd like to narrow it down to the disc's, if it is the disc's before I go buying new ones. Thanks,
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      10-04-2011, 11:11 AM   #2
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I know you probably don't want to do this, but if you really don't know where the problem is, try installing your OEM brakes, if the problem goes away, then you know its your AP set up.
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      10-04-2011, 01:06 PM   #3
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Does it vibrate with no brakes applied?
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Let me get this straight... You are swapping out parts designed by some of the top engineers in the world because some guys sponsored by a company told you it's "better??" But when you ask the same guy about tracking, "oh no, I have a kid now" or "I just detailed my car." or "i just got new tires."
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      10-04-2011, 02:19 PM   #4
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Unfortunatley I don't have the stock brakes anymore, at the time I got rid of them there was no vibration when applying the brake.

But the vibration was in the steering wheel from when I installed the BBK with spacers. At the time, all indications pointed to just an inbalance or the spacers causing the vibration only, not the AP brakes.

So now only option is probebly to replace the front disc's. I don't see how it can be anything else.
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      10-05-2011, 11:00 PM   #5
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This sounds similar to the problem I had with my PFC rotors. They didn't fit tight enough on the hub and ran in a very slight eliptical pattern because they were impossible to center. The center hole was only out of spec by fractions of a mm but that was enough to cause a wheel shimmy at 80 + mph. The best way to check for it is to rest your finger on your caliper with your nail dragging along the rotor while it's spinning. The pfc rotor caught my nail as it rotated off its axis. My multiple sets of stock rotors have all run perfectly true.
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      10-06-2011, 05:22 AM   #6
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That's a very interesting point. I have a dial guage and will be checking disc run-out but I should be able to check the rotational run-out also in place of my finger so I can get a more reliable reading. I never thought of this as I'd figure these brake disc's are pretty damn tight tolerance designed. But worth the check.

By the way, what type of brake disc's are "PFC"?
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      10-06-2011, 09:23 PM   #7
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Quote:
Originally Posted by BimmerRob08 View Post
That's a very interesting point. I have a dial guage and will be checking disc run-out but I should be able to check the rotational run-out also in place of my finger so I can get a more reliable reading. I never thought of this as I'd figure these brake disc's are pretty damn tight tolerance designed. But worth the check.

By the way, what type of brake disc's are "PFC"?
PFC stands for performance friction. Specifically, I was referring to their direct drive rotors. Sounds like you have a more precise method over my fingernail test, but that's all I needed to pick up on my issue
Keep us posted. These things sure can be an annoyance.
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      10-07-2011, 04:55 AM   #8
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ah, right. Performance Friction.
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      10-08-2011, 02:22 AM   #9
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Update. I used a dial gauge and measured both inner and outer disc faces of both front disc's while installed. I measured several times each disc.

The right front disc has a run-out of 0.005" and the left front disc run-out is slightly over 0.004"

The directions with maximum run-out I have for APracing BBK disc's is 0.0003". See attached document.

I did not have a magnetic dial gauge such as in the instructions but used a standard one with vise-grip & adjustable extension which works fine for most disc brakes.

So, the tough question is, is 0.001" ~ 0.002" enough to cause the vibrations I'm getting? A tech rep at APracing says it's possible. If I get two new front rotors, I sure hope it fixes the issue.
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File Type: pdf APracing run out procedure.pdf (26.3 KB, 503 views)
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      10-08-2011, 02:34 AM   #10
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Quote:
Originally Posted by BimmerRob08 View Post
Update. I used a dial gauge and measured both inner and outer disc faces of both front disc's while installed. I measured several times each disc.

The right front disc has a run-out of 0.005" and the left front disc run-out is slightly over 0.004"

The directions with maximum run-out I have for APracing BBK disc's is 0.0003". See attached document.

I did not have a magnetic dial gauge such as in the instructions but used a standard one with vise-grip & adjustable extension which works fine for most disc brakes.

So, the tough question is, is 0.001" ~ 0.002" enough to cause the vibrations I'm getting? A tech rep at APracing says it's possible. If I get two new front rotors, I sure hope it fixes the issue.
The attached document states 0.003 not 0.0003. But since you mentioned the extra 0.001 or 0.002 it sounds like this was just a typo. You might try to check the run out in the other direction as well as the prior poster suggested. However since that probably is not a machined surface getting a good number may be difficult.

Also, first before replacing your rotors I would definitely have your wheels rebalanced. They can become imbalanced just from wear.
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      10-08-2011, 10:16 AM   #11
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Quote:
Originally Posted by swamp2 View Post
The attached document states 0.003 not 0.0003. But since you mentioned the extra 0.001 or 0.002 it sounds like this was just a typo. You might try to check the run out in the other direction as well as the prior poster suggested. However since that probably is not a machined surface getting a good number may be difficult.

Also, first before replacing your rotors I would definitely have your wheels rebalanced. They can become imbalanced just from wear.
Yes, typo. Thanks. I'm having the wheels rebalanced now and the day I had the dealer install the new ARC-8's and tires, they balanced it and still that evening first drive on the highway, I got the vibe. So at this point, It's got to be the rotors, I would think. Everything else has been checked out and is straight, tight, not worn, etc.
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      10-08-2011, 12:06 PM   #12
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Quote:
Originally Posted by BimmerRob08 View Post
Yes, typo. Thanks. I'm having the wheels rebalanced now and the day I had the dealer install the new ARC-8's and tires, they balanced it and still that evening first drive on the highway, I got the vibe. So at this point, It's got to be the rotors, I would think. Everything else has been checked out and is straight, tight, not worn, etc.
If I had that level of axial runout, I'd take the rotors off, polish up the mounting flanges and then remeasure them. The excess is very small and a little rust or even anti-seize compound between the faces would cause it.

However, I'd definitely measure the radial runout as well. Instead of measuring the face of the rotor, measure the outside edge to see if the rotor is off-center on the hub.
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      10-08-2011, 09:56 PM   #13
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Quote:
Originally Posted by JAJ View Post
If I had that level of axial runout, I'd take the rotors off, polish up the mounting flanges and then remeasure them. The excess is very small and a little rust or even anti-seize compound between the faces would cause it.

However, I'd definitely measure the radial runout as well. Instead of measuring the face of the rotor, measure the outside edge to see if the rotor is off-center on the hub.

Yes, in fact I actually did all that. Cleaned the surfaces with embry paper per AP UK's tech directions, ran both the radial and the axial run-out. Only the surface run-out was out on both a bit. I also took the rotors off before hand, cleaned all rust and anti-seize compount off, etc. Talked to Stilen today and they agree that although a small amount out from the max, it's most likely the front rotors, in fact they said it'll get worse, which it has since about May when I noticed the vibe at braking. Got two new ones in the mail. More to report when I get it all together and on the road again. Hopefully this will not be a waste of $$$!
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      10-08-2011, 10:33 PM   #14
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So the question now is what caused the runout to be out of spec? Were they bad to begin with? Or is that just how they wore?
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      10-08-2011, 11:33 PM   #15
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Quote:
Originally Posted by RickyBobby View Post
So the question now is what caused the runout to be out of spec? Were they bad to begin with? Or is that just how they wore?

I go round and round with that question Ricky. I never had the chance to track it after installing the BBK. Plus, these brakes only have about 6,000 DD miles on it. Right after initial install of the BBK last November with 12mm spacers for the OEM 18" to clear the calipers, it all of a sudden had a slight vibe at about 80+mph. but it did not feel magnified with braking. That started to happen about 3 months ago, or at least I noticed it about then.

I'm pretty sure if I can remember correctly, while I was in England with this M3 and had the BBK installed. I regularly cruised at 95+mph on the motorway there and braking didn't cause this issue, although I had the slight vibration/wobble in the steering wheel. Must have just started to ware like this I guess. Kinda strange though.
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      10-09-2011, 09:23 AM   #16
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Quote:
Originally Posted by RickyBobby View Post
So the question now is what caused the runout to be out of spec? Were they bad to begin with? Or is that just how they wore?
I'd be surprised if thats how they wore, many of us use this kit and have a lot of track and road miles on it.
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      10-09-2011, 02:51 PM   #17
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I'd be surprised if thats how they wore, many of us use this kit and have a lot of track and road miles on it.

Me too but I can't explain it.
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      10-09-2011, 08:52 PM   #18
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Have you tried another set of wheels?
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      10-09-2011, 08:59 PM   #19
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Have you tried another set of wheels?

Vibe started day after installation of the AP BBK with 12mm spacers and with OEM 18" wheels.

I now have ARC-8's with new tires, road force balanced and still had the vibe but like I mentioned in my earlier replies, the vibe is magnafied with braking. But that didn't start till about 3~4 months ago. So I think two problems though.

With the ARC-8's, I still have the vibration at 80+mph even when NOT braking. Braking only magnifies the problem. If that makes sence.
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      10-10-2011, 06:34 AM   #20
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I asked because with my ARC-8's and Hankook RS3's I have a slight vibration at highway speeds too. I had them balanced twice to no avail.
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      10-10-2011, 11:43 AM   #21
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I asked because with my ARC-8's and Hankook RS3's I have a slight vibration at highway speeds too. I had them balanced twice to no avail.

Ah damn! That is not good news. What else have you done to your M3? Does the vibe go away if you go back to the OEM wheels? Curious because then is it possible that this car can only accept it's own 18" and 19" wheels from BMW only and all the rest cause a vibe? That's nuts if it is.

Does your vibration magnify by braking though? This is where it's difficult to figure out if that's because of the wheels, which already there is a slight vibration at 80+mph cruising, or if it's the front rotors causing it.

Someone on the forum mentioned to me on a nother post about this issue that their BMW tech told them that a wider offset wheel causes an aerodynamic affect that causes this vibration. But I find that hard to believe it would be the cause at 80~90mph. the wheel is only sticking out about 12mm or so depending.

Well Stilen just sent me two new front rotors so it better be the fix.
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      10-10-2011, 12:38 PM   #22
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My OEM and Morr wheels (two different sets) are rock solid. I have Stoptech brakes by the way. On the track it isn't a problem and I have found that different road surfaces make it worse than others with the Apex/Hankook combo.

Do you think because the wheel/tire combo is lighter that is why we feel more vibrations?
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