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.
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.