Never had a single issue in years but today on the Chilterns the front was fading out.
I.e the lever slowly completely compressed to the bars giving me no power at all. Though letting go and giving them a gentle pump made them work a bit until the next decent.
I took the wheel out and drove home.
Now I'm back they seem fine, both pistons work evenly, fluid is full and no sign of leakage.
Had a problem with my Hopes
Sounds like air, so - full bleed + replace fluid.
The std 'air in system test' is, leave for a while
- test lever (ie pulllback)
- pump lever backwards and forwards for 30 secs and test
compare pullback. If after pumping lever is less back/harder indicates air.
Fluid is also hyrdroscopic (or something like that), it absorbs moisture over time, this means it becomes less 'hard' with age.
Old motorbike tip is to tap caliper when bleeding, it's supposed to shock any air bubbles free so they go with the flow.
Time for a bleed?
Brake fluid takes on moisture after a while apparently and needs replacing
I had exactly the same problem (explained here - http://cyclonembc.editboard.com/maintenance-bike-tips-f5/disc-brake-help-t887.htm)
The lever was gradually finding it's way to the bar, although a few pumps would get the pressure back again. Tried bleeding and replacing the fluid but it had no effect, there was no air in the system
Turned out the seal on the master cylinder piston was goosed. Instead of pushing fluid down to the brake, the fluid was coming back up into the reservoir. New seals were a couple of quid but it means dismantling the lever - not that hard really. Been absolutely fine since. This was on a Mono M4 but the culprit lever is identical.
This is the page I used to help me do the job. The master cylinder piston is the little thing next to the spring in the exploded picture with two black seals on it. I replaced both of them.
If it's only doing it on the descents, it's likely to be contaminated fluid (lowers boiling point of fluid, when heat builds up it boils earlier than it should and allows the lever to come to the bar). If it's been in there long enough to get contaminated, it's probably worth stripping, cleaning, regreasing seals with silicone grease too(maybe new seals too, only about £6 for the lot).
Sorry to hijack the thread but my hopes need bleeding too. How easy is it with the hope bleed kit?
hope kit is pretty easy but takes a moment to get it right.
Though to be fair bleeding it top down (normally) shouldn't be a problem
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