1150GS rear brake woes.

[beanwood]

About 18 months ago, my 1150GS was dug out from the garage for a blast after 4 months being laid up.
Rear brake proved a little sticky (Not freeing off properly) and it ended up hot enough to melt the final drive gaiter.
It has Brembo brakes, and is 1999, so fairly early. I've had the bike since 2001, and not had an issue previously - it now has just 54k on it - although much of that has been in winter on UK salted roads, so it looks RUBBISH with paint flaking off the cylinders....

Anway.... life got in the way, and Long story short - it sat unused until a month ago,when I finally had the time and money to address it.

First - replaced the rear gaiter as it was 'crispy' from the heat.
Then I stripped the caliper and freed up the sliding pins. Reassembled with grease, new pads and all rubbers.
Replaced the original flexi pipe with braided stainless.
Pushed out the pistons and they were unmarked, so they went straight back in.
Replaced the brake fluid, and bled the system.
Patted myself on the back for a job well done, and grabbed a beer (Or two)..

so - back to the story..

Rode it 3 miles for the MOT - passed no problem (Hoorah).
Rode it 3 miles home again, and can feel the rear brake starting to bind. By the time I got off, the caliper was VERY hot again.

Trying to diagnose the cause - took a 6 mile spin, withouth ever touching the back brake lever - and again it is piping hot.

This leads me to think rear brake is being applied, and fluid pressure isn't being released.
I've checked runout and it's under 0.2mm, so OK I thunk,
Gut feeling - it's a master cylinder issue - but how can I prove that before throwing money at it?

 

[hops]

Ensure the sliding pin on the caliper is free of rust and crud as they do have a tendency to bind (No. 7 on the attached).

Less likely: - Also check the final drive bearing has no play, if it gets excessive the wheel can effectively wobble and the disc can rub against the brake pads.

 

[DrFarkoff]

|Change the rear hose

They delaminate and start to act as a one way valve Holding the brake on

 

[fatbaldbob]

|Change the rear hose

They delaminate and start to act as a one way valve Holding the brake on

Replaced the original flexi pipe with braided stainless.

He did that as part of his brake rebuild.

Not that it helps; I had an 1150GSA that did something similar, it would randomly apply the brakes hard by itself but it would then release. Very dangerous and tried all the things you did to no avail. Is it a servo bike? I’m convinced that was the issue with mine. If so perhaps a servoectomy may help

 

[Neil W]

Posted about this ages ago , my mates r850 r did the same , after bleeding it would be fine for a few miles and then do the same thing :-

1. changed the fluid .... nope
2. replaced the rear flexi hose ...... nope
3 .put a spare known good rear caliper on it .... nope (stripped the original and it was actually fine )

It was the rear slave cylinder , there was a step on the cylinder wall caused by long term storage and the fluid containing water , the brake would work but the slave cylinder piston would start to stick and then even though the pedal returned the piston was not returning fully and was keeping the brakes applied .

New slave cylinder and original caliper and it was fine , if you are happy working with brakes it is easy enough to take off the slave cylinder and strip it to check if there is a wear pattern on it's cylinder bore

 

[DrFarkoff]

Posted about this ages ago , my mates r850 r did the same , after bleeding it would be fine for a few miles and then do the same thing :-

1. changed the fluid .... nope
2. replaced the rear flexi hose ...... nope
3 .put a spare known good rear caliper on it .... nope (stripped the original and it was actually fine )

It was the rear slave cylinder , there was a step on the cylinder wall caused by long term storage and the fluid containing water , the brake would work but the slave cylinder piston would start to stick and then even though the pedal returned the piston was not returning fully and was keeping the brakes applied .

New slave cylinder and original caliper and it was fine , if you are happy working with brakes it is easy enough to take off the slave cylinder and strip it to check if there is a wear pattern on it's cylinder bore

Rear Master cylinder Ya Mean But Yes a definite possibility

Yes I agree I was a bit knackered this morning and missed the brake line had been changed

But Between a step or the brake master cylinder teflon lining bit getting tight (Seen it quite a few times) OR someone has not left any free play at he pedal to master cylinder on the push rod???

 

[kirby morgan]

I had similar on a R1150gsa with the older 2 nipple abs ( not the servo one)
Rear gaitor went on fire, replaced it and brakes were still binding. So removed the abs modulator, reverted back to conventional brakes and no problem.

 

[beanwood]

He did that as part of his brake rebuild.

Not that it helps; I had an 1150GSA that did something similar, it would randomly apply the brakes hard by itself but it would then release. Very dangerous and tried all the things you did to no avail. Is it a servo bike? I’m convinced that was the issue with mine. If so perhaps a servoectomy may help

Thanks - no this isn't a servo bike as far as I know (How would I tell) but it does have the early ABS.

Rear Master cylinder Ya Mean But Yes a definite possibility

Yes I agree I was a bit knackered this morning and missed the brake line had been changed

But Between a step or the brake master cylinder teflon lining bit getting tight (Seen it quite a few times) OR someone has not left any free play at he pedal to master cylinder on the push rod???

I was tending towards the master cylinder, as there's rather TOO much free play from the pedal - it's about 1/2 an inch befor it even makes contact with the internals. I was thinking it's probably stuck somehow, although it does apply the brakes, and seems to release them afterwards.

Progress today - I took out the pin, and cleaned it so it was sparkly clean and shiny - and the rear brake was only warm after a 6 mile ride - not blistering hot. Still it was warmer than the front, so still some work to do I THINK.

Slightly concerned it may be the ABS II -so might have to consider removal kit of some kind.

 

[beanwood]

I had similar on a R1150gsa with the older 2 nipple abs ( not the servo one)
Rear gaitor went on fire, replaced it and brakes were still binding. So removed the abs modulator, reverted back to conventional brakes and no problem.

How did you remove it ? Did you use a kit?

 

[DrFarkoff]

Thanks - no this isn't a servo bike as far as I know (How would I tell) but it does have the early ABS.

I was tending towards the master cylinder, as there's rather TOO much free play from the pedal - it's about 1/2 an inch befor it even makes contact with the internals. I was thinking it's probably stuck somehow, although it does apply the brakes, and seems to release them afterwards.

Progress today - I took out the pin, and cleaned it so it was sparkly clean and shiny - and the rear brake was only warm after a 6 mile ride - not blistering hot. Still it was warmer than the front, so still some work to do I THINK.

Slightly concerned it may be the ABS II -so might have to consider removal kit of some kind.

On the nose pedal travel! 1/2 inch? Master Cylinder Piston is stuck up the bore and not releasing pressure!!

Never worry about Lifting out the ABS Its a big magnetic clutch plunger thing and actually pretty okay if you need to get stopped in the wet (as long as you stay off white lines ! No Pleasing some people

 

[beanwood]

On the nose pedal travel! 1/2 inch? Master Cylinder Piston is stuck up the bore and not releasing pressure!!

Never worry about Lifting out the ABS Its a big magnetic clutch plunger thing and actually pretty okay if you need to get stopped in the wet (as long as you stay off white lines ! No Pleasing some people

The thing is - even though logic tells me it's stuck - it DOES appear to apply and release pressure ?
That's why my thoughts moved to the ABS - as accoring to Clymer it applies pressure to both front and rear - even if only the front is used - and that would explain how it was still hot after my ride without touching the back brake?

 

[DrFarkoff]

The thing is - even though logic tells me it's stuck - it DOES appear to apply and release pressure ?
That's why my thoughts moved to the ABS - as accoring to Clymer it applies pressure to both front and rear - even if only the front is used - and that would explain how it was still hot after my ride without touching the back brake?

Does your ABS have 2 bleed nipples on the ABS modulator or 6 ?? OR another Do you get two big red rectangular lights flashing on and off in sync above each on your "dash" when you switch on? This is ABS 2 It will be fine and has no effect on your braking if it fails

Perhaps yours has 2 dissimilar lights? One of which blinks fast and then settles to a steady light, Whilst the other just blinks on and off ?? (This is Integral or servo assisted braking and will scare the poop outta you if you wants brakes and they have failed BUT the nice wee warning light will tell you before you should need them!) this version also whirrs loudly when the brake lever is pulled with the ignition on !



Only the integral ABS applied both from the front lever

 

[DrFarkoff]

The thing is - even though logic tells me it's stuck - it DOES appear to apply and release pressure ?

When the fluid gets hot from the pads being partially applied, there is no relief port and the pressure just increases and applies more braking effort and then you get very hot pads

I had a dozen of these in my workshop over the years If you drop the boot off the master you will likely see it is a white plastic in the lower part this swells and is a Barsteward to get free Even a used MC will be enough to confirm the theory

 

[beanwood]

Does your ABS have 2 bleed nipples on the ABS modulator or 6 ?? OR another Do you get two big red rectangular lights flashing on and off in sync above each on your "dash" when you switch on? This is ABS 2 It will be fine and has no effect on your braking if it fails

Perhaps yours has 2 dissimilar lights? One of which blinks fast and then settles to a steady light, Whilst the other just blinks on and off ?? (This is Integral or servo assisted braking and will scare the poop outta you if you wants brakes and they have failed BUT the nice wee warning light will tell you before you should need them!) this version also whirrs loudly when the brake lever is pulled with the ignition on !



Only the integral ABS applied both from the front lever

Thanks - I have only two nipples on the ABS unit - and the 2 lights flash on and off - so ABS 2 seems right (Along with Brembo brakes front and rear). You've allayed my fears about total brake failure though (...which I never had until I started looking for problems...).

This is the bit in the manual that quotes the rear is also applied:
"All ABS II models are equipped with the partially integral system. Applying the front brake lever automatically applies both the front and rear brakes. Applying the rear brake pedal applies only the rear brake."

I'll have a go at the master cylinder, and decide whether to add that to the Motorworks shopping list, along with the QD fuel connector that failed tonight....

 

[beanwood]

no relief port and the pressure just increases and applies more braking effort and then you get very hot pads

This makes perfect sense. Thank you.

 

[Neil W]

Posted about this ages ago , my mates r850 r did the same , after bleeding it would be fine for a few miles and then do the same thing :-

1. changed the fluid .... nope
2. replaced the rear flexi hose ...... nope
3 .put a spare known good rear caliper on it .... nope (stripped the original and it was actually fine )

It was the rear slave cylinder , there was a step on the cylinder wall caused by long term storage and the fluid containing water , the brake would work but the slave cylinder piston would start to stick and then even though the pedal returned the piston was not returning fully and was keeping the brakes applied .

New slave cylinder and original caliper and it was fine , if you are happy working with brakes it is easy enough to take off the slave cylinder and strip it to check if there is a wear pattern on it's cylinder bore

Sorry meant to type master cylinder