2 Hydraullic Brake mechanic questions

Hey guys,

Sorry for the jong question, but since getting married about 9 months ago, I've inheritted the mechanic duties of my wife's bikes in addition to my own. When we pulled her mountain bike off of the hook this spring, there were a few things that needed to be done, especially to her Hayes Nine brakes. Front brake needed to be bled, and she needed new pads and rotors front and back.

I bled the front brake without too much trouble, but noticed after bleeding that when I pushed on the round brake caliper pistons with the box end wrench (per Hayes instructions) to make room for the pads, I saw a little brake fluid coming out from around the round pistons. I thought, at the time, that perhaps it was just a little hydraulic fluid left over from the bleed. I cleaned it up I tested with the old pads and old disc and everything seemed to work fairly well.

When I went to swap out the old pads with new pads, I needed to do the same thing with the box end wrench and the brake caliper pistons and this time I noticed that a lot more brake fluid was leaking around the piston. I assume that this is not normal.

Question 1: Any idea why I'd see leaking here and how do I fix it?

The rear brake seems to be operating properly, but when I try the box end wrench trick, the pistons rebound to their normal position when I pull the wrench out. As a result, there isn't enough room for new pads and a new rotor.

Question 2: Is there any reason why the rear pistons wouldn't be working properly and is there an easy fix?

Thanks in advance.

Seth

1
its leaking because the piston seal is bad
maybe it got too hot or went through too many heat cycles or just was dry and hot and dirty for too long?
who cares, its bad, youll probably need to replace it
How does the brake work though?
Does the lever feel spongy?
If it works and feels fine, maybe its fine?
though dont go ride DH with it to test it....id still want to replace the seal if this was mine

2
maybe its the piston o-ring squirming\twisting?
did you try to lubricate it with some brake fluid or something?
dab it in around the piston with a toothpick or something and then *lightly* actuate the lever to move the piston in and out a bit to work the fluid in there. see if it helps?

other than that, if its returning like that, it could be a return spring somewhere in the system
someone more hayes savvy will have to comment.

I always had issues putting new pads on 9s. I'd typically push the pistons in with the lever bleed port open and the hose attached to push some fluid out. That would give me enough room for the new pads, but it also required a rebleed. Shimming the pads and squeezing the lever typically just resulted in the bleed plug on the lever shooting across the room. Mags never required this step, but 9s always did...for me.

Quote:

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Originally Posted by bagtagley

I'd typically push the pistons in with the lever bleed port open and the hose attached to push some fluid out. That would give me enough room for the new pads, but it also required a rebleed. Mags never required this step, but 9s always did...for me.

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should have mentioned this

if you bleed with worn pads, top off the fluid, and have a system with very little "give" on the master cylinder side, theres no room for the fluid to go and you will have to remove some, the best\easiest way is which as bags described.

though instead of springing back, the pistons will just hit a wall where they wont compress further into the caliper. this is so much fun to deal with on automotive calipers (insert sarcasm)

That explains issue 2 perfectly, thanks. I'll give that a shot.

As for issue 1, is it difficult to replace the seals? It seems that the fluid comes out only when I'm pushing on the calipers with the box end. If I then clean it up, put (in this case old) pads in place and pump the brakes, they work properly. No more fluid comes out. Is it worth risking a new pair of pads to determine if it's going to leak anymore?

Thanks for the help guys.

hayes 9's I wouldn't spend too much money on ... the newer brakes like the juicy 5's/7's/even the BB7 mechs are much better IMO

Quote:

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Originally Posted by sethschmautz

That explains issue 2 perfectly, thanks. I'll give that a shot.

As for issue 1, is it difficult to replace the seals? It seems that the fluid comes out only when I'm pushing on the calipers with the box end. If I then clean it up, put (in this case old) pads in place and pump the brakes, they work properly. No more fluid comes out. Is it worth risking a new pair of pads to determine if it's going to leak anymore?

Thanks for the help guys.

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well, what you might be doing, is tweaking the piston as you're pressing it back into the bore so its going in kinda crooked and creating a leak path around the seal

throw the new pads in there and give it a whirl
like i said though, ride something conservative

clean them very well before this ride, and if they leaked again and you see dirt collecting there (sign of a leak), definitely replace the seal.

should be somewhat easy to replace a seal, though ive never work on them
essentially just pop the piston out, you can use the brake lever to help this out.
then, remove the old one, put in the new one (lubricate it with the brake fluid first though), and put the piston back in and you're good to go.
shouldnt be but like 5$ in o-rings and 1hour of your time.

rebleed them of course

another trick ive used in the past to remove caliper pistons is to remove the caliper from the hose, drain the fluid, and then give it a quick shot of compressed air from where the hose connects. should pop em right out. place a rag around it before you do this so you dont go shooting parts accross the garage or into your eye.