Issues with bleeding Shimano hydraulic brakes

[weisan]

I ran into two issues with bleeding my rear Shimano hydraulic brakes (BR-RS805)

1. I couldn't push fluid into the bleed port from the caliper after loosening the bleed screw. The cup on the shifter is opened. I have no issue doing this on the other caliper in the front following the same steps or procedure.

2. When I squeeze the shifter, it will soften at first then when I retract the lever and squeeze again, it hardens or won't move much.

What could be wrong?

[HenryA]

Have you tried adding fluid from the top? If you have a syringe and hose, you can suck from the bleed nipple while someone else adds fluid at the top. This might get you around whatever’s going wrong.

[bikinchris]

Whenever I have trouble with bleeding a Shimano brake, I use the two syringe method and push fluid both ways.
But it sounds like your master cylinder has a problem with obstruction or failed bladder. There are no parts available to buy for that.

[45K10]

I agree with bikinechris it is probably the master cylinder
I have had the same problem in the past. I tried the two syringe method and it would work for a couple of pulls of the lever and then the pistons and the lever would not move. I ended up replacing the whole brake assy include a new hose.
I really like Shimano transmission parts but their brakes are not as reliable IMO. My wife has Sram brakes on her MTB and they have been great.

[isaacneff]

Another vote that it is probably the master cylinder stuck in the lever. Try adjusting the lever reach in and out to see if that allows the piston to move enough to push fluid past, sometimes that works. Otherwise, you have to rebuild the lever, which really isn't a Shimano supported service.

[weisan]

Thank you everyone for chiming in, I will tinker around a bit and report back.

[weisan]

New issue came up:

Fluid leaking out from caliper.

[eippo1]

Originally Posted by weisan

New issue came up:

Fluid leaking out from caliper.

Did you have the port open at the lever at the time of the leak? Could be excess pressure if no.

Or can you check the position of the pistons? One or both may have extended past the seals. Push them back hard and see if it still leaks. If it does, it may have damaged the seals.

[benb]

Originally Posted by isaacneff

Another vote that it is probably the master cylinder stuck in the lever. Try adjusting the lever reach in and out to see if that allows the piston to move enough to push fluid past, sometimes that works. Otherwise, you have to rebuild the lever, which really isn't a Shimano supported service.

Does shimano require you to set the reach to a certain distance from the bar for bleeding like SRAM does? That's a good thing to check.

[benb]

Originally Posted by eippo1

Or can you check the position of the pistons? One or both may have extended past the seals. Push them back hard and see if it still leaks. If it does, it may have damaged the seals.

How does that happen? Shouldn't there be a bleed block in there?

[eippo1]

Originally Posted by benb

How does that happen? Shouldn't there be a bleed block in there?

Yes there should be, but it can happen if things are over pressurized and then the bleed block is removed. I know because I managed to do it when first doing my own bleeds. Messed up the seal for me and I had to trash the caliper. I was being lazy and trying to fix a spongy lever and didn't fully open things up so knew exactly what I did wrong when it all went to hell.

[weisan]

.

[weisan]

I am still a bit confused. How can I tell whether it's the shifter lever that has gone bad or the caliper? Is there a "test" that I can perform to verify?

[Carbonita]

Bisection iteration. Cut hose. Apply pressure or vacuum to caliper with the end of hose in fluid reservoir. Caveat, I've not had this problem, just musing.