1100RT Massive rear caliper faiure

[DonSydney]

Hi guys,

 

Coming back from a weekend away today, and all of a sudden the rear brake starts to drag.... heavily. Pedal is rock hard. Unfortunately I had no tools with me (very rare) and couldnt do anything about it on the side of the road. Was 40 miles from anywhere, on a quiet road, so had to press on, albeit carefully. By the time I got to where I could do something I'd totalled the rear caliper from the friction and heat. I'll pick up a replacement caliper with no problem, but has anyone got any idea what would cause this ?

 

Don

 

[ahirsch]

Did the caliper come unfastened? I have had one of the bolts holding the caliper to the frame work loose and the caliper then dragged on the disk.

[DonSydney]

Nope, all tight....

[Selden]

Something like this happened to me once with a Honda. About a mile from home, I noticed the bike starting to slow dramatically; I stopped and found that the rear disk was very hot, and the wheel would not turn. I loosened the bleeder, and brake fluid gushed out, freeing the wheel. When I got home, I disassembled the caliper and found a small piece of dirt blocking return flow -- hydraulic fluid could go in, but not out. The problem never recurred. I have no idea where the dirt came from, but it's a good example of why it pays to be meticulously clean when changing brake fluid.

[John Ranalletta]

Don, on my 1100 RT, the rear caliper would not retract after use which might be what happened to yours. I remember disassembling, cleaning and lubricating the moving parts of the caliper assembly with anti-seize. Sorry, I didn't retain the photos, but it's likely this was not a sudden failure but and eventual one as the brake pad has probably not retracted properly for a while.

[tomk99r11]

Similar thing happened to my 99RT. Prepping for a trip I changed rear tire, did some other stuff and somehow must have futzed with the abs sensor/adj on the side. The test ride after all of my prep resulted in the caliper seizing, got very hot. Ended up replacing the sensor (NOT CHEAP) and rebuilt the claiper, the rotor was okay. Been fine since. Learned to be certain to NOT touch anything unless doing so purposefully (had to be MY screw up, oh the agony of admission).

[cycleman]

If you haven't kept up with bleeding of the brakes this can happen. The reason is that over time brake fluid attracts water/moisture and as it heats up can result in brakes locking up as the mixture expands due to the heat. Normal clean brake fluid won't do this.

 

The clue was that once you loosened the bleed screw you let the pressure off and the brakes worked normally. Still would require fluid change ASAP.

[T__]

Don, the usual cause of similar brake pressure build up is the master cylinder take up port hole blocked either due to dirt/crud blocking the small hole or improper adjustment of the master cylinder (or pedal up stop) so the piston won’t fully return & uncover the hole..

 

There is a very small hole just in front of the master cylinder piston when it is fully retracted.. That hole serves two purposes,, first it allows new fluid to enter the cylinder just in front of the piston to allow the fluid to keep the system completely full.. Secondly it opens the piston bore area to the reservoir to allow any brake fluid heat expansion to flow back into the reservoir & not build pressure & apply the brake..

 

If that hole is blocked for any reason it will allow system pressure build from heat then slowly apply the brake more & more as the fluid heats up & expands,, the more it expands the more it applies the brake..

 

Check the rear master cylinder to brake pedal adjustment & also check the brake pedal up stop adjustment.. If all OK then verify the small hole is open.. If all OK then your problem is somewhere else like sticking caliper or possibly a delaminated rear brake hose internal liner making a one way valve of the hose liner..

 

 

 

 

Twisty

 

[DonSydney]

Thanks Twisty.... maybe thats my problem. A few weeks ago I raised the height of the rear pedal (I like it up high). Havent really been on a good long run until the weekend that I had the problem. Fingers crossed it's that simple.

 

All I have to do now is source a replacement caliper, which is proving more difficult than I imagined it would be.

 

Don

[nldaniel]

I saw a similair problem on the front brakes of a K1100LT once.

Turns out the rubber hoses were degrading. The flaking bits had plugged the banjo bolt, so you could force fluid past the blockage by pulling the brake, but it could not get out.

 

looked like this:

 

 

the fluid was terribly cloudy as well, so you should see it if it's something this bad..

[Joe Frickin' Friday]

Thanks Twisty.... maybe thats my problem. A few weeks ago I raised the height of the rear pedal (I like it up high). Havent really been on a good long run until the weekend that I had the problem. Fingers crossed it's that simple.

 

I can just about guarantee this is the problem, then. 6 years ago another board member did the same adjustment, and subsequently go the rotor so hot that the rubber boot between final drive and swingarm caught fire.

 

I've made the same adjustment to the front brake lever on my R1100RT, and I was able to confirm that the little master cylinder port was still uncovered by taking the lid off of the reservoir, and watching for a "geyser" of brake fluid when I squeezed the lever. That geyser was a little bit of fluid being pushed out of the master cylinder before the piston finally covered up the port and started delivering pressure/fluid to the caliper. If you don't see that geyser when you squeeze the lever, then you know that you've got the port covered even with the lever at rest, which is (as you've discovered) a bad deal.

 

It's harder to test the adjustment on the rear brake, since you won't see the geyser: the master cylinder is too far from the reservoir. I think that for the rear brake, the only way to confirm an open bleed port with the lever at rest is (with brake pedal fully up) to verify that you are able to push the caliper pistons in. That means having the caliper off of the rotor, and prying the pads apart with a stick/screwdriver/frozen bratwurst. PITA, I know, but it beats roasting a brake caliper.

[DonSydney]

........That means having the caliper off of the rotor, and prying the pads apart with a stick/screwdriver/frozen bratwurst. PITA, I know, but it beats roasting a brake caliper.

Really not a problem at the moment lol

 

Don

[Tony_K]

Listen to what everyone has been saying and I'll just add on this bit.

 

The 1100's are getting OLD. If you still have rubber lines ditch them for teflon steel braided ones now. This should be done even before a failure. So other riders on 1100's take heed.

[DonSydney]

I'm having all sorts of trouble finding a replacement for the 1100 caliper. Anyone know if the 1150 caliper is the same ? I have a line on one of those, but I'm not sure.

 

Cheers

Don

[T__]

Don, I’m not sure either.. The part numbers are different but the internal piston size is very similar..

 

The 1100 rear caliper is a Brembo caliper & the 1150 rear caliper is a BMW caliper made under license from Brembo.. I’m not sure if the mounting or offset is exactly the same or not..

 

Maybe a call or E-Mail to Beemer Boneyard will yield you the info you are looking for as they are very good at what fits what;

 

customerservice@beemerboneyard.com

 

Tel:(973)775-3495 M-F 10am-5pm Est

 

 

Twisty

 

 

[BeemerBerg]

+1 what Tony said.

I was bleeding the brakes on my '99RT to day, and noticed a lot of little black flecks in the fluid. I'm guessing the original rubber brake lines are deteriorating. If these clog up the brake lines, it would certainly cause excessive pressure build-up, and not allow the piston to retract. Heat.

[DonSydney]

Well waddaya know.... the 1150 caliper bolts straight up.

 

Now for something interesting.........

 

Given that I left all the fluid all over the road when it finally let go, I decided that I'd reverse fill the lines (from the caliper up with a syringe) to get things started. So I fill the syringe, fit the appropriate sized tube to the nipple, back of the nipple, and press the syringe. Nothing would flow !

 

So then I readjusted the height of the brake pedal (as suggested by a few here) and viola..... fluid flowed through to the reservoir.

 

I'm not taking to the bank the fact that that was the problem, but it would appear to indicate that it was.

 

So my next question........ how many years do I have to pump the pedal for before I get some pressure up ? I've read in other places about the infamous 'BMW pump the pedal till your arm drops off waiting for pressure to build'

 

Don

 

[DonSydney]

OK, been doing some more reading (love this site )

 

Too late to do it tonight,but I'm thinking that the best way to get this sorted is to open the bleed nipple at the ABS and pump fluid from the caliper until it comes out the ABS ?

 

Then maybe give them a good bleed, and then another after a ride ?

 

Don

[OoPEZoO]

Yeah, bleeding the system on the 1100 when it is dry can be a real beeotch. I fought with mine quite a bit when I installed my stainless steel brake lines. I filled from the reservoir to the ABS nipple, then from the ABS nipple to the caliper. I then finished off with a straight bleed from the reservoir to the caliper. It can be a pain, just stick with it. Once you get some pressure in the system, it goes much quicker.

 

If you have a syringe, I would stick it into the hole in the reservoir and push fluid from there. I've always been funny about back feeding fluid through brake lines........especially when there is an ABS pump involved.

[DonSydney]

OK, brakes are back. Bled to the ABS, then the caliper. Still not 100% happy with the pedal pressure, but I'll take it for a ride and do them again.

 

Now, just to complete my humiliation...... here's a photo of the old caliper assembly.......

 

 

dc