UPDATE - Seized caliper piston
I have 2 bikes - winter/commuter running disc brakes and summer running rim brakes. The past week I've had to commute on the summer bike whilst I was waiting for new tyre for the commuter. Because the summer bike has been in hibernation I've not really noticed, but back on the commuter this morning my rear disc brake is as good as useless.
I'm assuming that I've glazed the pads, although when originally fitting the brakes I made the same effort with the rear as the front to bed them in and all seemed well.
Am I right in thinking that I can sand the surface of the pads down slightly to take off the glazing, or should I just pull the trigger on a new pair?
Should add, the brakes are Acor (Juin Tech) semi-hydraulic.
I'm assuming that I've glazed the pads, although when originally fitting the brakes I made the same effort with the rear as the front to bed them in and all seemed well.
Am I right in thinking that I can sand the surface of the pads down slightly to take off the glazing, or should I just pull the trigger on a new pair?
Should add, the brakes are Acor (Juin Tech) semi-hydraulic.
0
Posts
Sanding them as you suggested.
Folks on here seem to think glazing a pad is as simple as flipping a burger
They are more likely contaminated (oil, dirt...)
ANyway, the cure is the same... sand them
Just use water to rinse them, and Isopropyl alcohol to clean the rotors if they need it.
There is no secret ingredient - Kung Fu Panda
London Calling on Facebook
Parktools
Marin Nail Trail
Cotic Solaris
Eventually took the caliper off and had started investigating - seem like one of the pistons is seized as only 1 pad is moving. No wonder it wasn't working. I took off the front too just to compare and the pistons are both moving freely on that one.
Didn't really know what to do, so tried soaking it in hot water hoping some gunk was just stuck somewhere, but this hasn't worked.
Any other ideas to free it before I contact the shop to get a replacement?
Try soaking it in something other than just water. A degreasing agent like GT85 or Muc Off (if we're going for brand names) should help.
Bikes: Donhou DSS4 Custom | Condor Italia RC | Gios Megalite | Dolan Preffisio | Giant Bowery '76
Instagram: https://www.instagram.com/ben_h_ppcc/
Flickr: https://www.flickr.com/photos/[email protected]/
Oh well, fingers crossed it won't be me next
Need to speak with the shop, but considering getting a refund and return to the Spyre's I still have in the garage (although the Acor's are better stoppers and less lever travel).
I have heard numerous stories about these brake calipers, most of them horror ones, as I was about to buy a set of them. throw them away and get yourself a set of HY/RDs. they are, in their present version, flawless.
Annoyingly, when I bought them last autumn the internet wisdom was they are a godsend... fingers crossed they won't give me grief... the good thing is that I have them on my single speed, which hardly does any descending
If there is no load on the pistons (they arn't squeezing anything) then its vanishingly unlikely the two have the exact same stiction, so one will start to move first and continue to move while the other doesn't, that does NOT mean its faulty.
The way to diagnose a seized piston is if the disc buckles over rather than the second piston starting to move once the first is starting to push on the disc. Seized pistons more often seize out than in as the seal force to retract them is much less than the hydraulic force pushing them out.
When fitted and I pull the lever only 1 piston moves. It doesn't move when the other has made contact with the disc - it just doesn't move. There is only 1 pad "slowing" me down.
Same when it's off the bike - only 1 piston will move.
The caliper that is/was working moves both pistons at the same time (on and off the bike).
I literally spent hours on sat trying to fettle and centre the caliper - replacing cables etc.
^ wot he said. The hydraulic fluid will take the path of least resistance. Its unlikely that both pistons have exactly the same resistance, so without anything to push up against, one piston will almost certainly move before and/or more than the other. If the difference in resistance is significant enough, one may not move at all until the other piston comes up against a hard object.
And as he said, they normally stick on rather than off. It would have to be seriously stuck to not come out.
If that is the case then taking the piston out, cleaning out any debris and making sure it is oiled around the sides and seals (with the same hydraulic fluid) and fits properly so that it moves freely. This is really the only way to be sure it should work fine. When I had some Avid Juicy 3s that constantly gave me problems, we had to hit one piston with a block of wood and hammer to get it to move at all at one point!