Front Rotor Runout Limits?
 

Hi Guys,

I am trying to solve a problem with my R1100S shuddering under braking. I bought a fancy dial gauge and it appears that I have about 2/1000 runout on one caliper, and little or none on the other. My manual doesn't mention a spec for runout on the caliper, only minimum thickness. Is 2/1000 on a caliper significant, or do I need to look elsewhere?

Thanks,

Jim Moore

A few people have had good results just cleaning the rotors with a hone. Fits in a drill with dingleberry stones on the end of a wire. Google brake disk hone and you should find what you need.

I would hardly call 0.005mm significant on anything bolted to a motorcycle.

I jsut checked the rotors on my CBR (which works perfectly). They're about 10/1000. I think the rotors on the S are fine. Whew!

This reminds me of a BMW Motorrad engineer who once said about our beloved boxers: we never had issues with engines overheating, until we started to include oil temperature meters.

I had brake shuddering. It came from a bent front rim. It is also known to occur with shot front wheel bearings, or incorrectly tightened front axle (you need to pump the front suspension with brake applied before tightening the lower alen bolts on the fork bottoms, as per manual instructions).

Fixing wheel geometry has solve all and any brake shuddering without even honing the brake rotors.

Thanks Meeni. I'm getting some new tires this week so I'll check out all that stuff.

If that doesn't solve your brake shuddering try this thread.

http://forums.pelicanparts.com/bmw-r1100s-r1200s-tech-forum/600915-brake-maitenance-warped-rotors-my.html

over time brake pad material builds up on the rotor and needs to be cleaned off.

Runout can cause a high speed pulse, but THICKNESS differential will cause one at all speeds and much more noticeable.

The caliper has the capability of moving laterally with a warp, so it masks run out.

How does the caliper move laterally on the R1100S?

and sometimes "a little dab will do ya".

where the piston heads meet the back of the brake pad, put a dab of vaseline on there.
tends to keep things well shimmed and encourages wiggle room.
also attracts brake dust, so you need to get in there, clean and re-dab.

compressing the fork legs with the caliper bolts, axle and axle clamps snug, but not tight. i do a few pulls, then get them almost bottomed out using tie-down straps. zip-tie the front brake halfway pulled, then tighten the caliper bolts, axle and finally the clamps.
release the straps, release the hounds, see if it helps.
this procedure works really well with regular guy forks, but it's not quite as life changing on a bmw, since the front end is all that wizzy-wig anti-dive.

I stand corrected, thinking about my cars and the wife's 650. Needed another cup of coffee to wake up the brain after a late night. :cool:

Reasoning still works though. The calipers are fixed, but the disk is floating on its bolts. Not much, but you can try yourself, you'll see you can move it by hand and feel the spring washer pushing back. If your hand can, the piston can too :)

Usual brake cleaner and moderate buffing with 200 grit usually cleans pad deposit. Especially useful after fixing wheel geometry to see instant improvement. Otherwise it may take some time to even out the rotors. Careful, after cleanup, the brakes are not operating normally and need to be "set-in" again before braking power returns.

There better now!

Yet more maintenance I feel guilty about, for not doing it...