Rear brake pressure problems?

Bendy toy

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My back brake woes are not over.

I needed to use the bike so popped the old pads back and got about 1/2 mile before the back brake was jammed solid. Thankfully I had the sense to take a few spanners and allen keys.

The brake was jammed on. I mean jumping on the pedal jammed. Loosening the mounting bolts made zero difference, trying to lever the pads in case the caliper had stuck - ditto.

Eventually I loosened the hydraulic banjo and fluid squirted out. I left it slightly loose and managed to get home with the brake jamming up again.

I stripped the caliper but while the pistons were tighter than I'd like, they were not badly jammed. Ive taken out the seals, cleaned and reassembled with red rubber grease. The pistons move better but we shall see if they are the problem. It's the first time Ive had a rear brake jam solid in a few hundred yards.

So is it possible for the ABS unit to throw a tantrum and drive the back brake on hard? I don't have a 911 so does anyone know how to test it?

Bike is 2008 Adventure with ABS. 68,000 miles.
 
The plot thickens.

I was about to go for a ride to test the brake and it's jammed on again. So its not the caliper. I have also not run the engine since I bled the brake.

I've had elderly brake hoses delaminate internally but that was the old rubber/textile strand type. BMW OEM hoses are braided stainless and not especially old. I don't want to end up swapping parts until i find the fault.

Has anyone any idea what could cause the back brake to jam itself on hydraulically?
 
Restricted bore & hydraulic lock?

if the ABS unit was throwing a hissy fit, i would have thought you would have had light show on the dash?

if you crack the nipple is there pressure behind it?

could it be a seal failed in the abs module or caliper not allowing pressure to back off when the pedal / lever is released


Mart
 
I suspect hydraulic locking is the issue. - But where?

Backing off the bleed nipple blows away excess pressure.

Bleeding the brake seemed ok but testing the pedal action caused the brake to jam on. I had to crack the bleed nipple again to release the brake. it is the same ignition on or off.

Can the rear master cylinder cause this? Or do I need to look to the ABS module?

This afternoon, I had not touched the rear pedal when I had the brake jam up on the road.

I've not had any warning light from the ABS system.
 
Sounds like the master cylinder.
You haven't 'adjusted' the brake pedal height and adjusted the little threaded clevis on the master cylinder piston rod have you?
 
MattW said:
Sounds like the master cylinder.
You haven't 'adjusted' the brake pedal height and adjusted the little threaded clevis on the master cylinder piston rod have you?
Click to expand...

Not even touched the master cylinder since 2014 when I had the frame powder coated.

I hope it is the master cylinder but mine gets very little use so wont be wear n tear. I get more than enough back end braking from the linked system. I can guess the answer, but do you know if seal kits are available?
 
Ive had a chat with James Sherlock. Thinks its unlikely to be the ABS unit, more likely master cyl or hose @MattW suggests. I've bought a 2013 master cylinder for £50. I'll also need to get a hose elsewhere as they didn't have any in stock.
 
Master cylinder is my guess. You could try stripping it cleaning out and blow through with an airline.
 
Progress so far.

HEL hose and bleed nipple banjo bolt collected from their factory in Exeter. Brake slave cylinder arrived from James Sherlock off a 2011 bike. Replacement pads and retaining pin are all ready to fit.

Looking at HEL's new brake range a brace of their calipers would be nice. £800 to you sir for the fronts only, not asked about the back. Over spec'd bling? Certainly.
 
I ordered a new HEL brake hose but delivery is next week. Shame I didn't go direct to HEL - they are only just down the road from me.

New master cylinder fitted and all seems well. My old master cylinder had a nasty push-rod seal causing all sorts of crap to get inside.

The later spec cylinder has a much better corrugated gaiter over the push-rod.

I've used Ferrodo Platinum brake pads with a new retaining pin and spring clip. They are supposed to be long life but unlikely to beat sintered so I'll be watching closely. BMW non sintered pads were screwed in 4000 miles (long before I had hydraulic problems).
 
Bendy toy said:
Progress so far.

HEL hose and bleed nipple banjo bolt collected from their factory in Exeter. Brake slave cylinder arrived from James Sherlock off a 2011 bike. Replacement pads and retaining pin are all ready to fit.

Looking at HEL's new brake range a brace of their calipers would be nice. £800 to you sir for the fronts only, not asked about the back. Over spec'd bling? Certainly.
Click to expand...

Bendy toy said:
I ordered a new HEL brake hose but delivery is next week. Shame I didn't go direct to HEL - they are only just down the road from me.

New master cylinder fitted and all seems well. My old master cylinder had a nasty push-rod seal causing all sorts of crap to get inside.

The later spec cylinder has a much better corrugated gaiter over the push-rod.

I've used Ferrodo Platinum brake pads with a new retaining pin and spring clip. They are supposed to be long life but unlikely to beat sintered so I'll be watching closely. BMW non sintered pads were screwed in 4000 miles (long before I had hydraulic problems).
Click to expand...

You never cease to confuse,
 
For the hard of thinking.

HEL make a bleed nipple banjo bolt that works fine.
HEL make a brake hose that works fine (mine is on order)
The later model OEM rear master cylinder has a useful gaiter over the piston rod.
 
Bendy toy said:
For the hard of thinking.

HEL make a bleed nipple banjo bolt that works fine.
HEL make a brake hose that works fine (mine is on order)
The later model OEM rear master cylinder has a useful gaiter over the piston rod.
Click to expand...
Not really. In your first post you stated that you'd picked up the brake hose and banjo bolt. That was confusing.
never mind. Hope it gets sorted.
 
In that case, we are both confusing.

I ordered a HEL hose but delivery is way down the road. I'd not noticed the delivery date at Post 1.

In the end I've rebuilt with the OEM hose and it's all working. The HEL hose will be fitted when it arrives.

The upshot is that if you have a 2009 or older 1200, the rear master cylinder has a cover boot that's worse than useless (traps dirt and non removable). Later models have a bellows that protects better and can be removed for cleaning.

If you have an older bike with ANY signs of rear brake issues - check the master cylinder.
 
Whilst not familiar with this ABS system personally, I can recall chatting to a guy waiting on a repair ,who described the changes/complexities with the 2007 & 2008 system to me when I was tyre kicking at the local dealer some years back. He was suffering rear brake drag & the disc had been overheating, along with rapid pad wear.

I seem to remember his problem turned out to be a micro-switch at the pedal, that was either out of adjustment or had failed, which meant the ABS system thought he wanted a touch of rear brake without him actually using the pedal. I am not sure whether this could apply to the OPs bike, indeed I think the systems changed radically the previous model year. Hopefully this makes sense & wasn't just second hand dealer bullshit designed to mask some techs idiocy when pad changing.

Good luck finding the gremlin ........................ KEN
 
My 2008 Adv has no micro switch at the brake pedal. I do not know how the bike detects rear pedal being pressed but I guess the switching is done from the ABS unit.

The replacement (2011) master cylinder was a straight swap and solved the rear brake dragging issue. It's done nothing to deal with how the linked braking system hammers the back brake but to be fair that's how the factory calibrated the system. Changing that would need an expert with access to the firmware.
 
The older bikes had a servo ABS system. 2008 onwards have no servo and an ABS unit that looks just like those used on cars.

Brake bleeding is done just as you would for a non ABS system.

Mine does seem to be sorted. Near enough 70K miles from the master cylinder is not "that" bad except that I hardly need to use the rear brake pedal. The linked system uses it more than hard enough.
 
Bendy toy said:
The older bikes had a servo ABS system. 2008 onwards have no servo and an ABS unit that looks just like those used on cars.

Brake bleeding is done just as you would for a non ABS system.

Mine does seem to be sorted. Near enough 70K miles from the master cylinder is not "that" bad except that I hardly need to use the rear brake pedal. The linked system uses it more than hard enough.
Click to expand...

My Mk2 2007 bike was sans servo.
 
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