Strange R1100RS rear brake problem

[JimmR75]

My 95 R1100RS (with ABS) has developed a strange problem with the rear brake within the past few days.

 

The rear brake will work fine sometimes, but sometimes the pedal will travel full stroke with no brake application. The pedal will respond to "pumping" and develop pressure. I bled the rear brake system when this started and there are no leaks.

 

No ABS or other warning lights. The lights come on and reset normally at startup. The front brakes continually to work normally. All brake pads are well within wear limits.

 

The bike is new to me 3 months ago and I have 3500 miles on it now (57K

total).

 

I bled/purged front and rear brakes when I got it. Fluid was due for a change but not nasty looking.

 

Open to suggestions before I start taking anything apart.

 

 

[dirtrider]

My 95 R1100RS (with ABS) has developed a strange problem with the rear brake within the past few days.

 

The rear brake will work fine sometimes, but sometimes the pedal will travel full stroke with no brake application. The pedal will respond to "pumping" and develop pressure. I bled the rear brake system when this started and there are no leaks.

 

No ABS or other warning lights. The lights come on and reset normally at startup. The front brakes continually to work normally. All brake pads are well within wear limits.

 

The bike is new to me 3 months ago and I have 3500 miles on it now (57K

total).

 

I bled/purged front and rear brakes when I got it. Fluid was due for a change but not nasty looking.

 

Open to suggestions before I start taking anything apart.

 

 

Morning JimmR75

 

That sounds like a rear master cylinder problem (there was, at one time, a BMW bulletin on rear brake master cylinder problems but I can't recall if the 1100S was part of that bulletin). I'm no where near my shop this week so can't look for old paper bulletins.

[JimmR75]

Rear master cylinder is my suspicion as well.

 

If it is an internal (seal) failure I would expect it to just fail and also not be able to pump the brake up to pressure.

 

The intermittent nature of the problem and lack of leaks gave me caution before I started disassembling anything.

[dirtrider]

Rear master cylinder is my suspicion as well.

 

If it is an internal (seal) failure I would expect it to just fail and also not be able to pump the brake up to pressure.

 

The intermittent nature of the problem and lack of leaks gave me caution before I started disassembling anything.

 

Morning JimmR75

 

There are 2 sets of seals, external seal (that keeps the fluid in the cylinder) & the piston seal (that is what allows the piston to seal to the bore & make pressure).

 

You would think that if it was an air-in-the-system problem then you could pump the pedal & make some pressure.

[Claudio]

My 95 R1100RS (with ABS) has developed a strange problem with the rear brake within the past few days.

 

The rear brake will work fine sometimes, but sometimes the pedal will travel full stroke with no brake application. The pedal will respond to "pumping" and develop pressure. I bled the rear brake system when this started and there are no leaks.

 

...

 

Open to suggestions before I start taking anything apart.

 

 

I worked on a non-BMW bike that had a similar symptoms. Air in the line would give you a more consistent (non intermittent) sponge feeling so the issue is likely a hydraulic failure.

 

Most likely the master cylinder failure. A rebuild or replace of the rear master cylinder will likely correct the problem.

[TonyRS]

Can I piggyback on this thread as I would have titled my question exactly the same way!

 

This new-to-me R1100RS has pulsing sensation on the rear brake pedal when applied. Fronts behave normal without pulsation.

 

No ABS error lights(they do light up at start), brake fluid flushed recently and wheels turn freely front and back. ABS function normal on sandy surface using only the front(I didn't think of testing the rears at the time).

[dirtrider]

Can I piggyback on this thread as I would have titled my question exactly the same way!

 

This new-to-me R1100RS has pulsing sensation on the rear brake pedal when applied. Fronts behave normal without pulsation.

 

No ABS error lights(they do light up at start), brake fluid flushed recently and wheels turn freely front and back. ABS function normal on sandy surface using only the front(I didn't think of testing the rears at the time).

 

Morning TonyRS

 

You really should start your own thread as your problem is different & also for a different person. If we start answering YOUR problems here then it we will have 2 threads within this thread going 2 different directions.

 

Just start your own thread (you can name it the same if you like- The OP's problem here is hydraulic in nature & your problem seems to be mechanical.

[TonyRS]

I will do that DR:)

[JimmR75]

When the problem manifests itself I can pump the rear brake pedal and get pressure. It takes a couple of brake applications and it will build and hold pressure.

 

Other times the brake works perfectly normally.

 

I have bled it carefully and do not think it is due to air in the system.

 

Best source for master cylinder seals / rebuild kit?