Hot rear brake rotor

[kamike]

Here's another mystery
I took my 'LT in for the 12k "inspection" early this year. Got it back from the dealer and noted immediately that my gas mileage was significantly down. Also noted lots of noise from the rear caliper/rotor, and lots of brake dust on the wheel. Took it back and the dealer replaced the caliper (under warranty) - supposedly a stuck piston.

So I get the bike back, and gas mileage is still down - 38 mpg vs. the usual 45 to 47, performance is sluggish, and after about 400 miles, I start smelling something hot, and after just a few miles from a cold start, the rear brake rotor is really hot, and there is brake dust beginning to deposit in the wheel rim.

The bike is back at the dealer today. Just called and they are ordering a new caliper assembly. I am not inspired with confidence that they know what the problem is. How likely is it that two calipers can be bad?

Any ideas on what could really be the problem?

[mneblett]

The bike is back at the dealer today. Just called and they are ordering a new caliper assembly. I am not inspired with confidence that they know what the problem is. How likely is it that two calipers can be bad?

Any ideas on what could really be the problem?A 2000 with 12K miles -- how often has the brake fluid been changed? Low miles (i.e., infrequent use), plus moisture in old brake fluid = highly likely to have a frozen caliper piston(s). Happens with cars all the time. From the limited info so far, it sounds like the dealer's diagnosis is probably spot-on.

EDIT: I just realized I may have misread the "2LT" -- is this a 2000, or a 2002, or??

[kamike]

Thanks for the reply. It's a 2003. I mis-typed the post.

The bike was purchased essentially new 11/2004 with 650 miles on it. It's had all the factory-specified services by BMW technicians. I do not know if the fluid has been flushed and replaced. Generally, however, the feel of the brakes is firm, not spongy (as I usually feel with old fluid in my other motorcycles).

[mneblett]

Thanks for the reply. It's a 2003. I mis-typed the post.

The bike was purchased essentially new 11/2004 with 650 miles on it. It's had all the factory-specified services by BMW technicians. I do not know if the fluid has been flushed and replaced. Generally, however, the feel of the brakes is firm, not spongy (as I usually feel with old fluid in my other motorcycles).A 2003 -- could have been built as early as 6/02. So for up to 2.5 years, the fluid wasn't changed. At the 6k service, the engine/drive train oils were probably changed, but unless it's shown in the invoice, they probably missed the fact that the brake fluid was past due to be changed (brake fluid is done by time, not mileage). This means there's a possibility that the brake fluid is anywhere from ~3-4.5 years old. Add in its first 1-2 years with the rear caliper pistons sitting still in their bores 99.9% of the time, and no circulation of the fluid, and I still see a a strong possibility for a stuck piston.

[kamike]

Thanks for the feedback. I'll specifically ask if they flushed the system and installed new fluid. It never occurred to me that they wouldn't, especially since this is the SECOND new caliper installed for the same problem, the first replacement being only a few months ago.

[mneblett]

Thanks for the feedback. I'll specifically ask if they flushed the system and installed new fluid. It never occurred to me that they wouldn't, especially since this is the SECOND new caliper installed for the same problem, the first replacement being only a few months ago.Whoa! Significant new data point! :)

If they replaced the rear caliper just a few months ago, they had to pump at least enough fluid to refill the caliper. That means something else is causing the caliper pistons to remain applied (the caliper probably still needs to be replaced due to overheated piston seals, etc.). I wouldn't take it back at this point until they tell you what the actual cause is.

With this new data, I'd be very suspicious of something like a mis-adjusted rear brake light switch (assuming, of course, that it's not just a your toe resting on the brake pedal :)). The Integral/EVO brake system uses electric pumps to produce pressure in the wheel circuits. The pumps are started when the brake is applied (i.e., when brake light switch is actuated). That can result in constant pressure on the rear brake if the pump(s) are constantly running (along with premature pump unit failure).

Do you hear the pump motor running most of the time? Is the brake light on?

[kamike]

Mark,
Thanks for the post and sorry for the delay on my end in this reply

No I have not heard the distinct high-pitched wine of the pumps when riding (and not applying the brakes), but your idea is exactly what I was thinking too - something activating the pump.

So...the rear brake light switch also activates the pump?

Mike

[mneblett]

So...the rear brake light switch also activates the pump?Yes. There's actually two electric motors, and both can be started by either front or rear brake light switches. I have noticed that the front brake switch seems to be the touchier of the two. I'd suggest going to the front brake lever, and listen for the light "click" as the switch trips -- if it trips essentially the very moment the lever starts move, it may be that road vibration is causing the switch to activate the pumps.

[brucecha]

Mark,
Thanks for the post and sorry for the delay on my end in this reply

No I have not heard the distinct high-pitched wine of the pumps when riding (and not applying the brakes), but your idea is exactly what I was thinking too - something activating the pump.

So...the rear brake light switch also activates the pump?

Mike

A computer print-out of the evo brake test (that safety recall, a couple of months ago) will tell you how long (in min., sec.) the brake system has been activated.

[lnowell]

Here's another mystery
I took my 'LT in for the 12k "inspection" early this year. Got it back from the dealer and noted immediately that my gas mileage was significantly down. Also noted lots of noise from the rear caliper/rotor, and lots of brake dust on the wheel. Took it back and the dealer replaced the caliper (under warranty) - supposedly a stuck piston.

So I get the bike back, and gas mileage is still down - 38 mpg vs. the usual 45 to 47, performance is sluggish, and after about 400 miles, I start smelling something hot, and after just a few miles from a cold start, the rear brake rotor is really hot, and there is brake dust beginning to deposit in the wheel rim.

The bike is back at the dealer today. Just called and they are ordering a new caliper assembly. I am not inspired with confidence that they know what the problem is. How likely is it that two calipers can be bad?

Any ideas on what could really be the problem?

I had the same set of problems after work was done to correct the rear brake rotor 'cow bell'. Hot rotor, low MPG and I could hardly back the bike by leg power. The retaining clip had been bent to keep the pads against the rear rotors to stop the rattle - which it did to some extent - but it cause the problems you listed. Hope it is that simple. The "repair" I got (under warranty) really made me mad.

[kamike]

I appreciate you all taking the time to reply. I had no idea that one could get a "printout" of the brake test. Good idea.

When the bike is stopped, and on the centerstand (in neutral) the rear wheel spins freely. I would guess that rules out the bent-tab problem. I am leaning more to the opinion that there is something fishy about the brake fluid pressure when the motor is running. I should have checked rear wheel spin, in neutral, with the motor running....

Well, tomorrow, when the shop opens, I'll be calling with some additional questions. I still do not understand why they ordered a new rear caliper assembly, and why they think that will fix the problem.