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Last ride before Christmas I heard the grinding of metal on metal and the rear brake had no effect - no problem, pads must be low. Ordered some pads when I got home, didn't think any more about it.
Went to fit the new ones today, and the old pads look like this:
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The outside one looks barely worn, the inner one has no pad material at all. On the caliper, the inner piston is sticking out, I can only push it back in a mm or so and it returns by itself. There was no pad rubbing or other problems before, and power/lever feel seemed fine until the grinding sound.
Is this air stuck in the caliper or some other problem?
ta,
Simon
looks like one piston seal is knackered, holding one piston, and needs replacing. I'd replace both while you're at out, should be a cheap and quick job, just a bit of air to bleed out once you've topped the brake back up again
Surely not on a nearly new brake? This will be the first pad replacement on this set...
cant get replacment parts for shimano
Sounds like you're not pushing the piston back in square.
Give it another go to get it back in then try the brake with no pads in to seee what the pistons are doing.
If one pistons slower than the other hold the more active one back and work the slow one in and out a few times.
Then re fit and try again.
I dought very much that there's a seal problem.
looks like one piston seal is knackered
Nonesense. Its just a sticky piston.
1. Fit old, worn pads.
2. Using tyre lever/spoon handle hold the free moving piston in.
3. Pump lever a few times to push other piston out- careful though, too far and it'll pop out (fluid everywhere)
4. Clean and lube (using a spot of mineral oil) sticky piston
5. Rinse caliper and fit new pads
Are the brake pads quite new? Could it be that the material fell off one side (are they supa star pads ;o) ).. Just a thought.
just what the rock said, the same happened to my Deore 525's. But the piston was jammed.
Some WD40, chain lube a 10mm spanner and a screw driver got it sorted.
[b] DO NOT USE WD40 ON SEALS[/b]
Best thing to use is mineral brake fluid.
Take out the pads.
Put mineral brake fluid around the pistons (you should have got some with the brakes if they weren't OE ones).
With the caliper mounted either in a vice or on the bike hold back the piston sticking out with a 10mm spanner of a gurt big flathead screwdriver. Push really hard against it and pump the lever.
The other piston will free up, the other will go back in and your brake will behave.
Although the pad falling off the backing thing may be possible with all the road grit that's about.
Ta all - with a bit more force and a bug screwdriver the piston went back and it seems to be moving OK. But now the pads rub and the lever needs barely any movement to come on, think they'll need a bleed anyway.
Pads may need spaced with that bit of red plastic that came with the brakes. The caliper may also need centred.