Hi

My son took the front brakes off his bike (Hayes 9) cause he had bent his rotor and wanted to ride anyway!

We took the pads out 'cause they had nothing left. But the brakes were pulled while off the bike and I really had to work to get the pistons seperated. When I did get them apart I couldn't get them to both sit right back (which is what I needed to get the new brake pads in).

I let a little fluid out of the system and this let me get the pistons right back and install the new pads. I bled the system (using the syringe method) and that seemed to go fine. But when I pull the brakes now nothing seems to happen - sure the pads move a tiny amount but nowhere near enough to actually engage the rotor (we're talking a fraction of a millimetre here). So what have I done wrong?

I've tried adjusting for dead pull, I've tried pumping the brakes, nothing seems to make any difference.

Any suggestions? Could I have damaged the brakes while seperating the pistons?

Thanks

Brett

Sounds like you still have air in the system.

Because there's a return spring on the pads if they were pumped enough while off the bike the pistons may have slightly popped out and then back in and you got air in the system. It would also explain why you had to fight and let fluid out to retract the pistons.

Probably best to bleed from the bottome as per a new dry system and that'll purge the air out the top.

Bleed the brake caliper, then the lever. After that, use tape or a velcro strap and wrap the lever overnight to keep constant pressure on it. In the morning release the pressure on the lever and top off the resevoir.

Mike

Thanks for the posts guys - will try again tonight and let you know how it turns out.

Do you mean retention spring? Because Hayes calipers don't use return springs.
Air can't get by the piston seals unless the piston was somehow pushed all the way out - and then there would be Dot4 all over the place.
The resevoir in the master cylinder compensates for pad wear and the resulting piston creep.

The reason the pistons won't go back into their calipers is likely because someone bled the system improperly - they forgot to push the pistons in first.
The reason the system isn't working now is likely because there is air somewhere in there. Bleeding Hayes brakes can be tricky - especially with them still on the bike. Check out the service instructions here: https://www.hayesdiscbrake.com/support_downloads.shtml and follow them thoroughly. The angle of the components when you bleed is very important. You need to eliminate any spots where air bubbles might get trapped.
If that doesn't work, the most common mystery problem with Hayes is a damaged hose at the master cylinder - the hose gets snagged or pulled, the hose lining tears at the tip of the master cylinder fitting, and fluid flows between the layers of the hose instead of just through it. Sometimes you can see it bulge a little bit when the lever is pulled - a healthy hose won't do that. The solution is to unscrew the hose from the MC, trim a cm or so off the end, install a new compression fitting, reattach to the MC, and bleed the system.

Hi guys

thanks for all the help.

Second rebleed and I noticed fluid coming from the reservoir. Seems there is a in sized hole in the resevoir just next to the bleed hole. Any way to seal that up?

Brett

If some fluid gets spilled while bleeding, it can get into the gaps between the parts of the MC/lever and give the appearance of a leak. I mention this because if it wasn't leaking before, it shouldn't be now - unless someone disassembled the MC for some reason and reassembled it incorrectly.
Clean up the Dot4 with isopropyl alcohol right away - it will peel paint if left in contact for very long.

Torchy, you're right. I was confusing the Hayes with my Shimanos when I thought there was a return spring. There isn't and it's just that funky wire retainer over the pin on the piston that Hayes uses.