I’ve got some old Shimano SLX brakes from around 2002. I’m having problems with them in that the pistons aren’t reaching all the way out to the pads. I understand that after a bit of pumping they should sort or reset to near where the pads are, like a car does, but they aren’t doing it. I’m assuming the old seals are seized up or something. In order to fix this do I need to replace the inner o-rings or can I just replace the seals on the outside? I can find the seals for £5 but to replace the o-rings I need to buy the pistons and it’s more like £25.
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The square cross section seal is the one that flexes and pulls the piston back to a retracted position when you let go
The round cross section seal is a seal for fluid leaks
Having said that, a piston not coming out/ pumping out isn’t clearly a seal issue. It sounds more like the brake needs bleeding / more brake fluid added. What have you tried doing to fix these?
That’s what I’ve been reading but I’ve bled them a bunch of times now. The brakes are stopping the bike pretty well when the pistons reach the rotor. I don’t see any leaks so I think I’m just going to replace the square seal.
Stupid question:
Have you measured the rotor thickness?
From the description you’re giving it sounds a little vague what’s going on, but pads not properly reaching the rotor or stopping short can be a case of the rotor being worn past the limits. If it’s too thin then the pistons run out of movement before things work properly.
On a shimano system I believe the nominal thickness is around 1.6mm. The minimum should be stamped on the rotor, it’s usually 1.5mm.
Maybe I’m missing something, but isn’t brake bleeding/oil refill the first thing you should do? If no oil is leaking, maybe the seals are ok
Should have said but I’ve bled it three or four times. It’s not made any difference.
