Tyres, Brakes and Suspension » Front brake seized on at speed

Front brake seized on, caused by brake lever in wrong position and fouling on throttle cable preventing the lever from fully retracting.

That's the short explanation.

For those who have the time, below is a full story. A bit of a long dit but keep going if you are interested.

On tour in Spain and overnight in the hills it had been down to 4 degC. During the morning on the plains temperatures now up to 25DegC.
Cruising on a motorway at the lead of a group. In cruise at 95mph just passing some lorries. Cruise control light went off. Bike started to slow dramatically.
Returned to overtaking speed via throttle and passed the lorry. Bike not responding well to the throttle, felt as though it was running out of fuel. Pulled over onto hard shoulder.
As I slowed the bike came to an abrupt stop. I realised that the brakes were "on" by themselves. Looked down to the front to see smoke pouring off the front brake discs and that distinct smell of hot brake pads.
Put bike on centre stand. Could not rotate front wheel, absolutely solid. Took Leatherman to pads and eased them back off the discs. Now the wheel would turn again.
I was quick to get the wheel turning as I didn’t want the discs resting with brake pads firmly on while they were so hot for fear of warping the discs due to uneven cooling.
Tested brakes. Brakes (front and back) going on and off without any problem. Tested brakes again with engine running and all satisfactory.
My chum following said that just before I slowed, my brake light came on. One more test. All ok and off we went again.

My mind was in complete turmoil. What could have caused this problem that has now, apparently, gone away.
Stopped for lunch and called my BMW dealer in the UK. He had never come across such a problem and had no suggestions. Checked our next overnight stop and could see that there was a BMW dealer in the town. Good job they open late in Spain.
During the afternoon started to convince myself that the problem had "gone away". Very quickly reassured myself that a problem such as a seizing brake does not come and go and not to be so optimistically stupid.
I had now adopted a routine of regularly disengaging the clutch to prove that the bike was still freewheeling easily without any brake binding.
Mid-afternoon and brakes started binding again. Same evolution to release discs with Leatherman with further tests and off we went again.

Explained problem to BMW dealer in Toledo (my Heroes). Mechanic came to look at my bike and then looked at a nearby GS.
Came back to mine and pronounced that "Your brake lever is in the wrong position". My immediate thought was, "The man's a fool". (For UK readers, I even said it like Tony Hancock (in my head)).
The mechanic showed me that it it's present position the master cylinder and lever was rotated too far forward and when lever was released after braking, sometimes it just fouled the electrical cable from the throttle control and prevented the lever from returning fully 'home'.

A short explanation of the operation of a hydraulic brake now.
To allow for expansion and contraction of brake fluid in the hydraulic system, the master has a reservoir. The reservoir is connected to the system via a small vent hole in the master cylinder. When the brakes are applied the lever moves the master cylinder piston and thus compress the fluid and move the slave cylinders. However during the first mm of movement the piston first closes off the vent hole, otherwise the piston would just circulate the fluid between piston and reservoir.

Back to my bike.
The lever was not returning home on occasions and thus the vent hole was remaining closed off and not allowing for any expansion of the brake fluid. When I started in the morning the system and fluid was cold. During the day it warmed up and because it could not go anywhere else to expand it moved the slave cylinders out. The brakes were gradually applied and heated up the pads, callipers and fluid. Eventually the increase in pressure was sufficient to put on the brake light and switch off the cruise control. The rest is history. NB. The brake light switch is operated by pressure not by a limit switch on the lever.

The Fix
Out came a torex 27. Lever rotated back away from throttle cable and problem fixed. My hero mechanic allowed me to tighten the bolts. He had looked at the GS because he had first come across this problem on a GS where the lever was fouling on the guard.
It will be obvious that this problem is not unique to an RS but could happen on any bike.

Happy days and a few enjoyable beers that evening

I am the second owner.
It could have been like that from new. Unlikely
The clutch lever is at the same orientation at the re-positioned brake lever
The fixing bolts were tight and the lever was tight on the bar, it is not as though it slipped round.
It would need to have been either re-positioned by loosening the fixing bolts or
forced round perhaps when it was lashed down during transport.
It was lashed down on the ferry to Spain but they use a simple strap across the seat.

The other thing that could cause a problem like that is if there was air or moisture in the brake system and it expanded under the heat caused by heavy braking. But that story about the brake lever being in the wrong position is a new one of me.

I came across this problem in a ford transit many years back, a mechanic , I use that term loosely, because the pedal travel was considerable decided to adjust the master cylinder piston arm to raise pedal, this creating the same problem, no return for the fluid as he adjusted the piston beyond the fluid chamber hole.

As I drove the van down the road I thought ' this van has no power and it's getting worse ' all of a sudden there was a loud bang from the rear of the van and then no brakes, just smoke coming from rear drums, it applied brakes,, as the slave cylinder's heated through the the hot drums etc it expanded the oil and blew out the slave seals, a very anal experience.


Ged

Zitat von Grumpy Goat im Beitrag #5

---

Zitat von Varnish im Beitrag #3

---

I am the second owner.
It could have been like that from new. Unlikely
The clutch lever is at the same orientation at the re-positioned brake lever
The fixing bolts were tight and the lever was tight on the bar, it is not as though it slipped round.
It would need to have been either re-positioned by loosening the fixing bolts or
forced round perhaps when it was lashed down during transport.
It was lashed down on the ferry to Spain but they use a simple strap across the seat.

---

Strange that it did not happen on your very first ride of the bike.

---

I was also curious as to why it didn't happen on my first or earlier rides. I think boxter is right, the fault was hit and miss, sometimes the lever would return fully and on others the lever became trapped.
The Spain trip was the first time that I had been at speed for such a prolonged period and the range of temperature change of 4 DegC to 25DegC would not often be seen in the UK.

ABS saving grace, you are probably right. The ABS box of tricks doesn't care how the pressure to operate the brakes is being generated and it would have stopped a complete lock up if the pressure had built up sufficiently to initiate one.

I'm sure that there will be an ABS expert along shortly to explain everything and confirm or not