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For the first time in almost nine years of Shimano brake ownership I am having a problem. I have a set of XT brakes, M785s, which won't bleed- and by that I don't mean I have bled them and they aren't performing how I like but that fluid will not go through them with a syringe.
I have tried bottom up bleeding but this has ended up with the tube flying off and oil going everywhere and none goes into the hose and pit the other end. Top down and the fluid pours back out of the port on the lever.
Anyone know what's happening here? I have recently replaced the hose and it had been working fine until Sunday when the pads wore out. Now having tried to bleed them there's not enough pressure in the system to move the pistons much at all. However they do move so I know fluid is able to get around the system.
Thanks in advance.
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Uh oh, here come the Hope users...
Cable blocked? Disconnect it at one end and try putting oil into the caliper to see if it comes out?
Edit: Maybe not, it doesn't really make sense if you've just changed the hose but you can probably get higher pressure in the system when closed to force it by a blockage
Pitched or kinked line would have been my bet too. Are you doing this on the bike or removed the brake system and doing it from a bench /work stand.
One other thought is a snapped bleed nipple...top bit moving but bottom section sized and sheared off!!! Had this once on a car rear caliper........found out after much head scratching!
Blocked master cylinder port would explain the symptoms, you could try removing the reservoir cap and the membrane and see if fluid can flow from the cylinder into the reservoir.
l.e. You'll probably need a new lever anyway, might as well have fun with it.
The hose isn't kinked or clamped in the stand- it is still on the bike.
When the syringe is connected to the nipple and the nipple is open if I squeeze the lever then the fluid moves in the tube to the syringe so I assume the nipple is in one piece.
Because if it bleeds you can kill it!
Got to be the other end then! Time to dismantle the master cylinder end of things.....good luck!
Are you opening the bleed nipple enough? The Shimano instructions say 1/8 of a turn, but on my XTs I had to open it at least 1.5 turns to get any flow, that was the same on front & rear.
Dookey- yes, fluid is coming out. I opened it about two turns.
Master cylinder faff it is then. Booooo.
All of your evidence is pointing towards the transfer port between the reseroir and master cylinder being blocked, probably by it's piston not returning fully for some reason.
Hmmmmmn. That sounds likely as I have had an incident or two where the lever has refused to return. Any idea how to sort that?
new lever probably. The piston seals can get sticky and not return under the spring pressure. I've just had a problem with mine.... You can manually push the lever back but the piston doesn't always go with it...
It might be worth as noted above just taking the cap off and seeing if there is anything obviously wrong... 25 quid on CRC for a new lever isn't so bad.
One thought, not sure what if any difference it would make in this case, but have you wound the free stroke adjust screw out? It's the recommended way to bleed them.
That's what I was about to suggest. Mine wouldn't bleed unless I did this. I can't remember offhand whether the lever has to be close to the bar or far away, but try each end of the range.have you wound the free stroke adjust screw out
Have had this with Saints - blockage in the hose. Disconnecting the hose from the caliper and clearing the holes then reassembling sorts it every time
endurogangster - another 'Predator' reference....!
We're all gonna die.
Going off at a tangent, OP, why were you bleeding them for a pad change? Or did they feel wrong?
I never bother bleeding my brakes unless they feel wrong. Perhaps once a year I'll give them a good going over, but other than that nothing really needs doing.
The lever was pulling to the bar and there wasn't much power so I thought a bleed would sort it out.
I'll start with the free stroke tonight then get onto gradually more drastic things if needed. I normally do the screw out anyway but decided to leave it as I never felt it made any difference.
Checked for rocks ? 🙂
* sorry had to ask!
I have had this in the past with one of the many M785 brakes I've run.
This:
... is the problem.coatesy - Member
All of your evidence is pointing towards the transfer port between the reservoir and master cylinder being blocked, probably by it's piston not returning fully for some reason.
Caused by this:
The piston seals can get sticky and not return under the spring pressure. I've just had a problem with mine.... You can manually push the lever back but the piston doesn't always go with it...
Sometimes it is sufficient to just back-off the free stroke adjust screw.
Sometimes you also need to compress the lever and then let it "flick" open under fluid pressure. If it's got to this stage, you're looking at a new lever though.
[edit] I completely stripped, cleaned, lubed and re-assembled the lever assy before I reached that conclusion. At that point you can observe if the piston is moving freely through it's travel. The tell-tale symptom is black contamination in the fluid at the lever, probably associated with some degradation of the piston seal.[/edit]