- Joined
- Mar 18, 2006
- Messages
- 2,945
- Age
- 70
- Location
- Ilkley, W Yorkshire, UK
- Bike
- 2013 ST1300 A9
- 2024 Miles
- 000679
A fellow member reached out to me by PM with a binding rear brake problem, and we have spent a few happy hours on the phone, and he has spent many more not-so-happy hours in his garage trying to pin this down.
He had previously had the calipers apart and checked pistons, cleaned grooves, fitted new seals.
We have made progress, but the solution is not definite yet - particularly since it sounds as though there are two completely different issues.
The bike is a UK 04 ST1300.
We did the usual tests with the SMC applying the SMC while turning the rear wheel. SMC pumped up the rear outer pistons, wheel locked and never released.
That doesn't necessarily meant that the SMC is bad - it could mean a few other things as well, but the crunch came when the front leeft centre piston bleed valve was opened and the rear pistons could not be pushed in. But when the outlet port of the SMC was cracked open the reear outer pistons could be pushed in by hand.
So - new SMC ordered and fitted. And that test was repeated with success.
But the rear wheel is still only getting beteen half and one turn - with effort, after the brake pedal has been pumped up.
So we got it so that the wheel was locked (I say 'we', I'm on the phone while he is on speaker phone getting his hands dirty at the other end of the country).
We did the previous checks, and fluid is getting through the SMC from behind to be ejected through the front left centre bleed valve.
The front left centre piston can be pushed in by hand - so that confirms the rear master cyclinder comepnsation port is clear.
So with rear wheel locked, we opened the bleed valves to release the pressure. Nothing came out. The fluid is not under pressure. Therefore it is not fluid pressure that is locking the rear brakes.
So we have concluded that the problem is nothing to do with pressure build up, but is a mecahnical issue.
The caliper without pads is sliding smoothly on the slider pins all the way in and all of the way out.
There are no marks on the rear stopper bolt.
There was no rifling in stopper bolt hole
Pads are brand new OEM, brand new pad springs, brand new chromed retainer clips, brand new pad pins with rubber grommit.
When the pad chrome retainer clip was fitted , it felt slack - so I guess there is some wear in the recess to accomodate the clip.
The owner had removed the slider pin in order to remove the caliper.
There was no binding in the movemenet of the caliper towards and away from the wheel.
We are thinking that somewhere along the line, something has not been fitted correctly and this has resulted in deformation of the caliper (unlikely I think), or the caliper bracket. We think that when the pedal is pumped up in order to meet with any resistance, the action is forcing something to sprain - into a position from which it cannot release. Spinning the wheel does enable the pads to release a bit - but not enough. He has verified that the brake disc (rotor) is not warped.
He is going to try to observe what happens at the caliper when the pedal is slowly pumped. But we are suspecting that the rear brake caliper bracket is bent slightly.
At least we are hoping that is the case rather than the slider pins being cross threaded or bent (the caliper moved back and forth smoothly).
Its easy for me to suggest this - but it is £200, and it still may not solve the problem if it is the pins.
Am I missing something obvious ??
He had previously had the calipers apart and checked pistons, cleaned grooves, fitted new seals.
We have made progress, but the solution is not definite yet - particularly since it sounds as though there are two completely different issues.
The bike is a UK 04 ST1300.
We did the usual tests with the SMC applying the SMC while turning the rear wheel. SMC pumped up the rear outer pistons, wheel locked and never released.
That doesn't necessarily meant that the SMC is bad - it could mean a few other things as well, but the crunch came when the front leeft centre piston bleed valve was opened and the rear pistons could not be pushed in. But when the outlet port of the SMC was cracked open the reear outer pistons could be pushed in by hand.
So - new SMC ordered and fitted. And that test was repeated with success.
But the rear wheel is still only getting beteen half and one turn - with effort, after the brake pedal has been pumped up.
So we got it so that the wheel was locked (I say 'we', I'm on the phone while he is on speaker phone getting his hands dirty at the other end of the country).
We did the previous checks, and fluid is getting through the SMC from behind to be ejected through the front left centre bleed valve.
The front left centre piston can be pushed in by hand - so that confirms the rear master cyclinder comepnsation port is clear.
So with rear wheel locked, we opened the bleed valves to release the pressure. Nothing came out. The fluid is not under pressure. Therefore it is not fluid pressure that is locking the rear brakes.
So we have concluded that the problem is nothing to do with pressure build up, but is a mecahnical issue.
The caliper without pads is sliding smoothly on the slider pins all the way in and all of the way out.
There are no marks on the rear stopper bolt.
There was no rifling in stopper bolt hole
Pads are brand new OEM, brand new pad springs, brand new chromed retainer clips, brand new pad pins with rubber grommit.
When the pad chrome retainer clip was fitted , it felt slack - so I guess there is some wear in the recess to accomodate the clip.
The owner had removed the slider pin in order to remove the caliper.
There was no binding in the movemenet of the caliper towards and away from the wheel.
We are thinking that somewhere along the line, something has not been fitted correctly and this has resulted in deformation of the caliper (unlikely I think), or the caliper bracket. We think that when the pedal is pumped up in order to meet with any resistance, the action is forcing something to sprain - into a position from which it cannot release. Spinning the wheel does enable the pads to release a bit - but not enough. He has verified that the brake disc (rotor) is not warped.
He is going to try to observe what happens at the caliper when the pedal is slowly pumped. But we are suspecting that the rear brake caliper bracket is bent slightly.
At least we are hoping that is the case rather than the slider pins being cross threaded or bent (the caliper moved back and forth smoothly).
Its easy for me to suggest this - but it is £200, and it still may not solve the problem if it is the pins.
Am I missing something obvious ??