New e34 rotors installed, but...

I just did my own front brake job on a '95 525i. At 105k rotors had to go. Worst part was breaking the carrier bolts loose. There appears to be some
shimmy in the front end and I can see why - apparently the rotors have to be centered on the hub. Why would they have so much play? I'll remove the wheels again and try to reset the hex bolt. Is there a tool that BMW techs use for this purpose? I tried to get it right, but it must not be exact. Any advice would be appreciated.
John
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The rotor bore is a good fit on the hub, so no centering is possible. If they don't locate without any play, maybe they're the wrong discs. Maybe E39 rotors have similar dimensions, apart from the bore which I'm pretty sure is 1mm larger in diameter.
Why would they have so much play? I'll remove the

There are no special tools needed to replace the rotors. Just spanners and a 7mm hex key. Mike.
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The only centring you need to do is to make sure the mating surfaces are clean.
Usual cause of shimmy is worn suspension bushes.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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wrote:

While that may be true, the bushings would have been worn before the rotors were installed, so the shimmy should not be a new symptom after brake work.
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OP didn't make it clear if the symptoms were there before or not. Many think because the shimmy is only noticeable when braking it must be a fault with the brakes themselves.
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wrote:

Another possibility for the OP "shimmy" is whether his wheels are balanced? On my 90 535i, 5spd, 110K, my original control arm bushings appeared to be fine. I swapped out the rotors and balanced the wheels and surprise - no more shimmy!
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No, there is no special tool, and that bolt is not entirely necessary. All it does is hold the rotor on while the tire is removed.
I just installed new rotors (all 4 of them) on my 3 Series, and I have xsome shimmy as a result also. I'm going to consider two things, 1.) there is dirt and corrosion on the hub preventing the rotor(s) from laying flat and true to the hub, and 2.) the rotors are not machined true from the manufacturer, which is an annoyance.

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xsome
dirt
manufacturer,
Assuming it's not 2, which would be terrible - I've used cheap discs and not had problems, but later I found that ATE discs, which are OE, were not very expensive - you could try lightly sanding the hub face before re-fitting the disc. As well as that, I lightly wipe the surfaces with grease and spin the disc on the hub to even it out. Seems to work. But what I found on my E34 was that little imbalances would make the steering wheel shake but the root cause was worn suspension bushes. Replacing a brake disc, or balancing the wheels, would help for a while but it always came back, until I got bits of the suspension replaced.
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I knew I'd get some answers here, always a good place to start!
The rotors came from BMW and there was no shimmy before the rotors went on, control arm bushings have been replaced recently, with new tires all the way around
The fact is that there is some "play", in fact several millimeters of back and forth until the hex bolt is tightly fastened. While lining up the new rotor lug bolt holes with the hub, some movement besides the circular rotation is there. Maybe the parts monkey sold me the wrong parts. I'm going back to BMW today.

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hands@your_throat.com wrote:

There shouldn't be any. That bolt is superfluous. The disk should be a snug fit on the hub.

It begins to sound like it. -- C.R. Krieger (Been there; done that)
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If that is only rotary 'play' that's OK. The bore in the rotor should be what is called a 'free fit' on the hub. IOW it should be virtually the same diameter as the location diameter on the hub without being tight.
While lining up the new rotor lug

If there is any movement other than rotary, once the rotor is fitted to the hub face, there is something wrong. The most likely reason is that the rotor is not the correct one for your car.
BTW. The hex Allen screw holding the rotor to the hub is only there to hold the rotor in position when changing a wheel. It has no other function. The book says to tighten it securely. Personally I only lightly nip them up with a little copper based grease on the thread. Makes them easier to remove, and once the wheel is on it's not going anywhere.
Maybe the parts monkey sold me the wrong parts. I'm going back to BMW

As I said. If the rotor has any lateral 'play' IMO that's your best bet. Mike.
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