I always seem to have a problem replacing pads in my Guide REs. I push all the pistons back, put the pads in but then one set of pistons pop out making it very difficult to get caliper over disc. Usually the front two are ok but the back two won't stay in. I usually end up juggling a screwdriver to even start the pads over the disc and often giving it a tap with the rubber hammer.
I don't have this problem with the 4pot Shimanos on the other bike. What am I doing wrong? Is there a trick to it I haven't seen?
Get a very wide flat object that ensures both pads (front and back) are pushed back at the same time...
Get a very wide flat object...
You may find that a worn out, soon to be discarded set of old brake pads are just the right size for this.
I have this problem with my SRAM Rival callipers. They won’t go fully back, or at least they push back but immediately pop out a mm or so and then the rotor won’t fit in between new pads. This is with the bleed screw out at the lever (and a syringe screwed in) so it’s not overfill causing it.
1) Clean off the pistons with brake cleaner and then dribble some DOT fluid on them so they retract through the seals smoothly.
2) Push the OLD pads in with a wedge shaped drift or a big flat screwdriver and leave it in there for a couple of minutes so the seals don't just spring back. A big Allen key works well too as you can rotate it and the lobes act like a cam on the pads.
3) Install new pads and enjoy.
Same method I've always used with all brakes regardless of brand and number of pistons.
SRAM say NOT to lubricate the pistons though…
oceanskipper
Full Member
SRAM say NOT to lubricate the pistons though…
Sram are wrong. I've just got a new* set of Guides that wouldn't work properly, following Srams advice, until I put a tiny amount of lube on the pistons.
*very obviously been sitting on a shelf for years
Over filled brakes are also surprisingly common.
Sram are wrong
Riiight. They say it because the seals are not supposed to move along the pistons as it drags dirt inside and wears the seals out. So while it might loosen a sticky piston it’s not the answer as it will then end up leaking at some point . Trouble is I don’t know what the correct answer is either.
FFS, page did something weird and deleted my post before I could submit. Here’s the concise version
- DOT fluid isn’t lube, it’s not made to stick to stuff
- You need to remove all the residue you can or you could contaminate your pads
- The film left is microscopic as the tight seals remove almost everything. There’s nothing left to gather dust.
- The official Sram piston advancing technique was doing nothing after many cycles. 2 new brakes being worked on
- The seals are supposed to move along the pistons. This is required to account for pad wear.
- Id wager Sram’s lawyers are concerned that someone cleans badly and contaminates the brake, leading to attempts at suing.
- Hope even have YouTube videos of them lubing pistons.