My college-age son (Austin, Texas) needs rotors replaced on
his 95 325I, and doesn't want to spend $400. (Pads were
replaced a few months ago, and he put off spending on the
rotors.) I'm handy with tools, pretty mechanical, and have
tackled water pumps, alternators, starters, etc. on American
and Japanese cars, and motorcycles, but haven't done brakes
(except on motorcycles). What advice can you offer on
replacing rotors on a BMW. I have heard the hard part is a
bolt that secures the rotors, and sometimes it must be
drilled out. Any advice would be appreciated. Any
specialized tools needed?
It's a cinch. All you need is the hex wrench (comes in any
metric set - 3mm or so?), some anti-seize, a screw-driver
or clamp to push back the pistons, and a 17mm (IIRC)
socket (works on the lug nuts, too) to release the calipers
so they will swing off the rotors.
Don't forget to replace the wear sensor (it's about $5)
on the side that has it.
You've pretty much got the bit already that can be a pain. Only advice I can
give really is to try and undo that rotor to hub bolt (which requires a
hex/allen key type head) before removing the pads and calliper. That way
someone can stand on the brakes to stop the rotor/hub turning while you are
trying to undo it. Which is a whole lot easier than trying to use
screwdrivers etc wedged into the rotor vents. Oh, and buy some new bolts
before hand so you have them already just in case you need drill them out.
Other than that, they are a doddle to do with no special tools required. The
calliper mounting bracket bolts are pretty tight too.
Last bit of advice is don't get BMW rotors, buy some after market brands. I
use the ATE Power discs, they are much harder wearing than the chocolate BMW
ones and cheaper too.
The screw may be a little tight. IME the best way to remove it, is with an
impact driver. Apart from that, about all you need is a spanner to remove
the two bolts securing the caliper mounting bracket, then slide the whole
caliper and mount assy off the disc, or rotor.
BTW, when you fit the new disc, the retaining screw only needs to be done up
lightly. It doesn't need to be really tight. It's only there to stop the
disc moving when changing a wheel etc.
Thing is, that on cars with wheel bolts, like BMW's, as opposed to those
with wheel studs and nuts, without the screw, there is nothing to stop the
disc revolving once the wheel is removed. If it did, it could be enough to
prevent the fitting of the wheel bolts when a wheel is replaced.
The screw we are talking about is 1.) very light, an d 2.) about as close as
is possible to the center of the hub as it can be. There is ample weight
spinning around near the edge of the tire that can counter this screw
without any problem.
We are talking a gram or two here, not ounces.
Not a gram or two. They 1/4 oz. (I just weighed one). And yes, a
weight that small would seem inconsequential. My thought was that I
don't want *any* unbalance in the hub assembly as the would have the
effect of adding to any imbalance in the wheels and there is no way to
measure or compensate for the hub misbalance other than "on the car"
balancing, which is an abomination and should be avoided if at all possible.
I had to cut one of those screws off once, and I can't tell that it's gone.
There is so much weight spinning a great distance from the center of the
axle, that this small bit of weight, effectively right on the center, is
going to be inconsequential in the grand scheme of things.
The lightest wheel weight I can ever remember seeing is 1 ounce, so a
quarter ounce isn't going to be a problem.
Rotors cost in the range of $50 each, and anybody with a sense of mechanics
can install them -- all of them -- in about 2 hours. The dealer, or a
mechanic with the proper assortment of tools can do it in much less time,
but those of us confined to working on the floor of the garage or in the
driveway tend to work a bit slower.
If you can do waterpumps, you can do rotors on a BMW.
It's a metric hex head countersunk setscrew, and yes, they sometimes seize
- although they may also have been damaged earlier by someone using an
imperial hex tool. However, they're easy to drill out as the hex provides
a centre for the drill, and they're fairly soft steel. Once the disc is
off, grind the rest of the head off (if needed), and remove the setscrew
from the back of the hub with Mole grips.
Use some copper grease on the new setscrew, and don't tighten it till it
groans. It's only there to stop the disc falling off when a wheel is
Also, make sure the mating surfaces on both disc and hub are perfectly
clean - any grit etc could cause run out.
Buy a set of metric hex heads for a 3/8 drive socket set.
*Remember: First you pillage, then you burn.
Dave Plowman firstname.lastname@example.org London SW
My experience is that after you drill the head off and get the rotor out
of the way, there is plenty of screw shank available to remove it out
the front with those "mole grips", which I assume are Vice Grips over
Even more to the point, if it is too loose it's not going anywhere with
the wheel installed.
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