Shimano Hydraulic Disc Brakes - Road

[creashor]

Hi

Hoping someone can help me.

I experienced a significant drop in rear braking power a couple of weeks back. The brake lever had no stiffness. It's a relatively new bike so rather than try to bleed it myself I took it to my LBS who bled it and all was fine. A hundred or so miles later, same thing happened.

I've tried to bleed it myself today and all is well up to a certain point. The stiffness returns to the lever, but when I reassemble the rear calliper and remount it to the frame the power has gone again. I've been extra careful in ensuring the bleed point is closed and topped up at the lever when I take the pot off.

The brake will engage and stopthe wheel but when I ride it doesn't stop me.

Anyone got any ideas what might be wrong?

Thanks

 

[DEFENDER01]

I have not had anything to do with the hydraulic brakes on a bike only cars which i guess work on the same principle.
Does sound like air getting into the system can the LBS do a pressure test.

 

[Yellow Saddle]

Bleeding brakes is not the panacea of all brake problems. You ONLY bleed brakes if the following scenario occurs:

You pump the brake lever and the pressure comes up and the lever stiffens. After an hour or so of no activity, the lever is "flat" again.

If that is not the case, bleeding won't help. Look for leaks in the line or fit a new seal kit to the master cylinder (the lever).

 

[creashor]

Thanks for the replies.

I have to say that it seems to me there is some sort of leak.

This is when I wish I had purchased at a LBS and not Wiggle!

 

[Yellow Saddle]

Thanks for the replies.

I have to say that it seems to me there is some sort of leak.

This is when I wish I had purchased at a LBS and not Wiggle!

A leak is very easy to spot. The line is full of oil and it can generally only leak at the end where it enters the caliper and the end where it enters the lever (under the tape). Have a look.

 

[creashor]

Just to finish off the story, LBS has confirmed a leak at the calliper end.

Thanks for all the replies.

 

[creashor]

Actually, I was wrong, it's at the lever end. I'm guessing that means a new lever

 

[Yellow Saddle]

Actually, I was wrong, it's at the lever end. I'm guessing that means a new lever

Not necessarily. Shimano levers are supplied in two stages of assembly. One, with the hoses attached and pre-bled (in spite of a centre attachement that can be trimmed for length) and, naked, without oil or installed hoses. Usually the leak is at the junction between hose and lever box. This will be evident if you lift the rubber hood and see oil in there. If the leak is at the master cyclinder, the oil will not leak onto the top of the lever between hood and box.
However, once the hood is contaminated with oil, it is difficult to fix and it will quickly stretch and become loose.

 

[Arjimlad]

I'm having a similar issue with my son's Shimano Deore rear brake and am a newcomer to hydraulic systems. This thread is hugely helpful.

 

[Yellow Saddle]

I'm having a similar issue with my son's Shimano Deore rear brake and am a newcomer to hydraulic systems. This thread is hugely helpful.

What's the issue with that one? Deore brakes are extremely, super, fantastically reliable.

 

[Arjimlad]

Gone very loose & spongy after the bike was dropped, to the point of being ineffective. The calipers close but not hard enough to arrest the disc.

The lever was too far out from the bars - but adjusting it in does not give enough bite to the brakes. I suspect the bike being dropped has ruptured or upset/bent something within the lever mechanism as it doesn't respond to pumping the lever at all. Perhaps bleeding/refilling the system may help, but I am leaning towards dropping £35 on a straight replacement of the caliper and lever with hose etc attached unless a bit of seal replacing can be done. From what I read online, servicing the seals on these brakes is not easy..

 

[Yellow Saddle]

To test whether bleeding will solve the problem, do the following.
Place the bike upright.
Pump the lever a few times and notice whether or not the lever feel becomes harder. If it seems to "pump up" after a few strokes, it means there is air in the system and a simple bleed can cure it.

If on the other hand, the lever is hard to start off with but goes soft when the lever is depressed and kept in, then the master cylinder seals are blown. These cannot be replaced.

 

[Arjimlad]

Thank you.