Disc brake calliper not fully retracting.

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Salty seadog

Space Cadet...(3rd Class...)
Hi, I have the Sram via GT disc brake system on my 2014 Whyte Montpellier. When I apply the front brake, after I release the lever I get a rubbing for a while which I assume is the calliper not reseating fully. It goes away after a while and can sometimes be cured by a couple of sharp pulls on the front brake.

Is there anything simple I can do to remedy this?
 
Check the brake for centering initially, does the rotor deflect at all? If yes slacken the calliper mounting bolts , squeeze and hold lever and retighten bolts.
If that didn't make much difference i'd pop the calliper off, whip out the pads and push the pistons right back. From what you're saying I'd expect the rubbing side to be quite stiff. If so I suspect new piston seals are called for.
 

arallsopp

Post of The Year 2009 winner
Location
Bromley, Kent
Are they hydraulic? If so, you may need to bleed them.

Quicker wins are
  • Cleaning the rotors (cloth, and lighter fluid does it, or specialist spray. Can stop high pitched sqeaks).
  • Reseating the caliper body (loosen the retaining bolts, hold the brake on and re-tighten. Stops squeaks that occur once per rev).
  • Cleaning the pistons (put a little dot fluid / mineral oil, according to the fluid you're supposed to be using, around the seal, and ease on off).
Edit - Cross post with rusty bearing.:smile:
 
Location
Loch side.
Are they hydraulic? If so, you may need to bleed them.

Quicker wins are
  • Cleaning the rotors (cloth, and lighter fluid does it, or specialist spray. Can stop high pitched sqeaks).
  • Reseating the caliper body (loosen the retaining bolts, hold the brake on and re-tighten. Stops squeaks that occur once per rev).
  • Cleaning the pistons (put a little dot fluid / mineral oil, according to the fluid you're supposed to be using, around the seal, and ease on off).
Edit - Cross post with rusty bearing.:smile:

How do you propose that a bleed or a clean or re-seating the caliper will help solve the problem?
 
OP
OP
Salty seadog

Salty seadog

Space Cadet...(3rd Class...)
Check the brake for centering initially, does the rotor deflect at all? If yes slacken the calliper mounting bolts , squeeze and hold lever and retighten bolts.
If that didn't make much difference i'd pop the calliper off, whip out the pads and push the pistons right back. From what you're saying I'd expect the rubbing side to be quite stiff. If so I suspect new piston seals are called for.

Are they hydraulic? If so, you may need to bleed them.

Quicker wins are
  • Cleaning the rotors (cloth, and lighter fluid does it, or specialist spray. Can stop high pitched sqeaks).
  • Reseating the caliper body (loosen the retaining bolts, hold the brake on and re-tighten. Stops squeaks that occur once per rev).
  • Cleaning the pistons (put a little dot fluid / mineral oil, according to the fluid you're supposed to be using, around the seal, and ease on off).
Edit - Cross post with rusty bearing.:smile:

Cheers guys, it is a once a revolution rub which suggests an out of true roter. Will have a look at that later although it must also in part be due to the caliper not reseating properly as it does go away as per the OP.
 
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arallsopp

Post of The Year 2009 winner
Location
Bromley, Kent
How do you propose that a bleed or a clean or re-seating the caliper will help solve the problem?

My thoughts were simply that if the pads aren't retracting, they're either not suitably motivated to do it (air in the lines mean that the lever release doesn't transmit to the pads, and you're left hoping that the spring is enough) or that they're unable to (because the pad movement is variable, and it could be that the dead-stroke, pad-gap-stroke, and contact-stroke isn't even on both sides. You can get a quick win by just reseating the calliper if that moves it into a position where the stiff side is compensated for).

As anyone who's ever ridden within a squeaks whisper* of my bike will know, hydraulics are a dark art I've not yet mastered.

* about 20ft if its dry. 3 times that if its been wet recently :smile:
 

fossyant

Ride It Like You Stole It!
Location
South Manchester
Rotors can be set right with your thumbs, or an adjustable spanner and a bit of sympathy, i.e don't move things too much. I explained this to a colleague this week, but he still shuffled off to the bike shop.... his new pads cost him triple what they should do. People go into blind panic with discs.... I only encountered discs with my kids bikes, easy to fix/set up and have been trouble free since I 'fettled them' on delivery.

My hydraulic discs have been mess free (much more expensive bike).
 
Location
Loch side.
My thoughts were simply that if the pads aren't retracting, they're either not suitably motivated to do it (air in the lines mean that the lever release doesn't transmit to the pads, and you're left hoping that the spring is enough) or that they're unable to (because the pad movement is variable, and it could be that the dead-stroke, pad-gap-stroke, and contact-stroke isn't even on both sides. You can get a quick win by just reseating the calliper if that moves it into a position where the stiff side is compensated for).

As anyone who's ever ridden within a squeaks whisper* of my bike will know, hydraulics are a dark art I've not yet mastered.

* about 20ft if its dry. 3 times that if its been wet recently :smile:

It doesn't work like that and bleeding is not a panacea for all brake problems. There is NO retraction mechanism built into hydraulic disc brakes at all. None. The lever has a return spring but it is decoupled from the master cylinder piston.

Brake pistons don't even slide in and out from the seals during braking. They only migrate through the seals with pad wear and right after installation or when they've been fully depressed by the mechanic when the hydraulic line is empty or open.

It is only a bit of flexibility in the entire system, from rubber seals to hoses to fluid that relaxes and the piston retracts somewhat, but without sliding in the rubber seals.

Brakes should only be bled when there is air in the system and the symptoms for that are very specific and cannot be confused with any other brake problems.
 
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arallsopp

Post of The Year 2009 winner
Location
Bromley, Kent
Fair on. Thanks for the pointers, @Yellow Saddle. For all my mechanical knowledge, they could be powered by pixies :smile:
 

lpretro1

Guest
a combination of trueing the rotor pushing the pistons back (with pad in situ) and recentering the calipers has sorted it. It seems though that often when taking out the wheel, after replacing there is sometimes the rub again.
That often hapens and it is normal just go ride
 
When pistons are pushed out the rubber seal is changed from square section to a square section leaning on its side (parallelogram), when you let go the lever the seals 'roll back', it's this that's mainly responsible for piston retraction. This is why you get pistons sticking when seals get tired.

My thoughts were simply that if the pads aren't retracting, they're either not suitably motivated to do it (air in the lines mean that the lever release doesn't transmit to the pads, and you're left hoping that the spring is enough) or that they're unable to (because the pad movement is variable, and it could be that the dead-stroke, pad-gap-stroke, and contact-stroke isn't even on both sides. You can get a quick win by just reseating the calliper if that moves it into a position where the stiff side is compensated for).

:smile:
 
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