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.
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.
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
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.
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.
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
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.
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