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      02-17-2013, 02:40 AM   #17
BimmerRob08
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Drives: 2008 M3, Space Gray
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Location: KIKR (ABQ), NM

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Quote:
Originally Posted by Malek View Post
Rob,

Thanks for the clarification. At the speeds you are describing, you can absolutely rule out the rotors being the problem. If it were the rotors, the vibrations would present themselves in the 45-55 mph range and would become amplified upon braking.

What I would say the problem is, first and foremost the technician "Road-Force" balancing the wheels doesn't know what they are doing. Next time they do it, make sure you watch them do it. Often times I have seen guys use the machine without the actual Road-Force drum because they are misinformed about the purpose of the drum.

Second, when the wheel is on the machine, make sure they are using a 5 lug adapter lock, and not a single center hub lock when they are mounting the wheel to the Hunter machine. This will ensure more hubcentricity when the wheel and tire is spinning and tire run-out is measured more accurately by the machine.

Third, while the wheel is spining, make sure the wheel is true. If you looks like its wobbling abnormally when spinning, this is not a good sign and the wheels aren't 100% true. I also recommend you have them pop the tire bead from the wheel, use a lot of tire mounting lube. You wouldn't believe how many times wheel/tire vibrations are caused from lack of lubrication during mounting and the tire doesn't actually properly seat against the wheel until many miles down the road. Remember, the Hunter machine is measuring wheel balance and tire run-out on what it measures. If anything changes, the previous balancing isn't effective anymore.

Lastly, check your lower control arm bushings. If these items are worn (which they shouldn't be), it will be the cause of vibration in the wheel.

Malek

Thanks Malek,

Well I did watch my tech do the balancing. I think from what I can tell he is very proficiant and experianced with the RFB. I know he spent all day the last time I had him balance the new tires by driving till the tires warmed up, remounting, etc. I can't say for sure if he used alot or little lube but I know he did. Also the mount is a 5 lug, not the center hub that you explained. I remember seeing him install lug nuts. Also he did a wheel run out and it measured as a "pass" on all four. Actually the rear wheels were marginal compared to the front wheels.

One strange thing I might not have explained exactly. Most of the time, depending on how smooth the highway is, the slight vibe in the steering wheel develps at about 78mph at times, then just smooths out mostly past 82mph and faster. But under braking, the vibration/wobble is manifested again under braking. So I think it could be the rotors. Especially since between the two AP rotor sets I have, one is allways worse than the other in terms of vibration under braking.

I had the tech about a month ago check the entire front end of the car out, no worn bushings or anything like that. I'm 99% certain its my brakes but we can't figure out what. Discs measure run out to .003", pads are new, calipers rebuilt, strap drive system on the rotors rebuilt. Even did a race-pad disc clean up and brake run in again. Still get that vibe at about 80mph at cruise and then under braking from faster speeds, the vibration is amplified. Disappears below 80mph when braking.

Real confusing.

Rob
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