paturoa
11th January 2012, 20:03
Well I'm stumped - help please....
Two rides ago the front brake was under performing, so I stripped and cleaned eveything. But I've done something wrong. For the last ride the brakes were binding and it was un-rideable. So I took out the bleed valve, swapped bikes with the spawn (she rode my bike) and I rode it with no front brake.
Conclusion #1 - I did something wrong.
It is an old DR 125 that I'm getting ready for a camping trip next week.
It is still binding on. I've cleaned (and I mean really cleaned!) the master and slaves, everything in between, and everything looks fine. Seals are fine, groves are clean, no goop anywhere. The slave piston moves freely, the master piston moves freely. I've blown compressed air thru the brake line and that is fine too.
I fill with new fluid and bleed, all as per normal.
Then the problem begins! Arggggghhhhh.
The symptoms are that the lever has pressure immediately, within 1 mm lever pull, and the pads never properly release from the disk. Lifting the front wheel off the ground and it needs serious effort to spin the wheel. When I move the caliper by hand I can see the pads are moving freely on the pins and move back from the disk. I can see that the location of the whole caliper assembly is correct for the disk. But there is immediate lever pressure still and it goes straight back to binding. This includes without spinning the wheel.
So I thought it was the slave end as the master end is so simple that I couldn't have cocked that up. I've tripple checked and the re-assembled. Same problem.
So my thinking yesterday was to start at one end and pregressively eliminate. Starting at the wheel for no particular reason ,other than I'd just pulled that apart 3 times!
- I removed the scraper o-ring from the slave and no difference. Piston nice snug fit with normal "stick-tion" on the seal.
- I blew air back through the brake line and was clear.
- Then pulled apart the master end again (x3) and all good still.
My current thinking is the master is the problem. ... as my understanding of how the brake works is ... that when the lever is released, that the master piston moves backwards (pushed by working spring) to a position where the system goes open to the reservoir. This also has a minor effect of lowerring the pressure in the line and "pulling:" the slave cylinder a small amount. This then releases any pressure and enables the slave to back off the pads and hence the disk.
When I look at it the front seal on the master piston can never reach the reservior hole, well that killed that theory!
So your assembled advise would be much appreciated as I'm out of enthusiasm to pull the sodding thing apart agin as I'm now out of beer and are drinking Mrs P's wine (oh the humanity!)
Thoughts please.
(and the tyre pressure is fine)
Two rides ago the front brake was under performing, so I stripped and cleaned eveything. But I've done something wrong. For the last ride the brakes were binding and it was un-rideable. So I took out the bleed valve, swapped bikes with the spawn (she rode my bike) and I rode it with no front brake.
Conclusion #1 - I did something wrong.
It is an old DR 125 that I'm getting ready for a camping trip next week.
It is still binding on. I've cleaned (and I mean really cleaned!) the master and slaves, everything in between, and everything looks fine. Seals are fine, groves are clean, no goop anywhere. The slave piston moves freely, the master piston moves freely. I've blown compressed air thru the brake line and that is fine too.
I fill with new fluid and bleed, all as per normal.
Then the problem begins! Arggggghhhhh.
The symptoms are that the lever has pressure immediately, within 1 mm lever pull, and the pads never properly release from the disk. Lifting the front wheel off the ground and it needs serious effort to spin the wheel. When I move the caliper by hand I can see the pads are moving freely on the pins and move back from the disk. I can see that the location of the whole caliper assembly is correct for the disk. But there is immediate lever pressure still and it goes straight back to binding. This includes without spinning the wheel.
So I thought it was the slave end as the master end is so simple that I couldn't have cocked that up. I've tripple checked and the re-assembled. Same problem.
So my thinking yesterday was to start at one end and pregressively eliminate. Starting at the wheel for no particular reason ,other than I'd just pulled that apart 3 times!
- I removed the scraper o-ring from the slave and no difference. Piston nice snug fit with normal "stick-tion" on the seal.
- I blew air back through the brake line and was clear.
- Then pulled apart the master end again (x3) and all good still.
My current thinking is the master is the problem. ... as my understanding of how the brake works is ... that when the lever is released, that the master piston moves backwards (pushed by working spring) to a position where the system goes open to the reservoir. This also has a minor effect of lowerring the pressure in the line and "pulling:" the slave cylinder a small amount. This then releases any pressure and enables the slave to back off the pads and hence the disk.
When I look at it the front seal on the master piston can never reach the reservior hole, well that killed that theory!
So your assembled advise would be much appreciated as I'm out of enthusiasm to pull the sodding thing apart agin as I'm now out of beer and are drinking Mrs P's wine (oh the humanity!)
Thoughts please.
(and the tyre pressure is fine)