Rear disc brake sticking, catastrophically so

[Dec66]

For some reason my rear disc (Shimano) has decided to intermittently engage itself, at pretty random intervals, with no input from me. Once it starts it gets worse very quickly until the brake is virtually full on, making me stop.

Then I get off, spin the wheel, and all is fine again, for a bit. Then it starts again.

Can anyone suggest a quick and dirty fettle that I could do armed with no more than a multitool, short of removing the cable (as I don't think it's an issue with the cable sticking)? I know YouTube is one's friend in such matters but it's firewalled at work and I don't have enough data to be streaming stuff.

Also, if that was you who I gave a mouthful to on Molesworth Street, SE13 this morning, after you gave me some backchat for having suddenly stopped, well I apologise, but you asked for it for being inconsiderate about a mechanical malady (maybe staying off my wheel might help, just a thought?)

 

[summerdays]

What happens if you apply the brakes lots of times for a short while then hold for 5 seconds? If that sorts it for a short while then look at loosing the bolts near the rotor, and hold on your brake lever whilst tightening it again? Someone else will explain that better than me!

 

[Dec66]

What happens if you apply the brakes lots of times for a short while then hold for 5 seconds? If that sorts it for a short while then look at loosing the bolts near the rotor, and hold on your brake lever whilst tightening it again? Someone else will explain that better than me!

Varies; the brake may free up, or lock on. I thought at first I could free it up by yanking the lever hard, but it doesn't seem to work now.

 

[summerdays]

Another option that happened to me when I let the pads get quite worn was the metal clip that was holding them in place dislodged and ended up jamming in the mechanism, grinding the wheel to a halt!

 

[roadrash]

have you tried to reset (re center ) the caliper as shown here

View: https://www.youtube.com/watch?v=V3uCGRAWG2M

 

[Dec66]

have you tried to reset (re center ) the caliper as shown here

View: https://www.youtube.com/watch?v=V3uCGRAWG2M

Can't watch that at present (see above)

 

[Dec66]

What I have done, however, is to examine the caliper and in its current position one of the pads is hard against the disc. I slackened the bolts and moved the caliper to a more suitable position, but when I tighten them again it puts the caliper back precisely where it was.

So, to get me home, I've left them slightly slack which allows lateral movement for the caliper, so it should not stick. Not ideal at all, but it'll do till I have more fettling time later.

 

[Scoosh]

That video is telling you 2 things to do.

1. Re-centralise the calliper - by slackening the bolts securing it to the frame; apply brake, tighten bolts while holding brake tight. You might need to do this a couple of times, apparently.
2. Re-Set the pistons - remove wheel, remove brake pads, use non-metal tool (old tyre lever) to push back the pistons as far as possible into their recesses. Replace pads and wheel - and it works fine*** !
3. Check if rotor is bent ...

HTH and you get home safely !




*** allegedly ... it does in the video !

 

[Dec66]

That video is telling you 2 things to do.

1. Re-centralise the calliper - by slackening the bolts securing it to the frame; apply brake, tighten bolts while holding brake tight. You might need to do this a couple of times, apparently.
2. Re-Set the pistons - remove wheel, remove brake pads, use non-metal tool (old tyre lever) to push back the pistons as far as possible into their recesses. Replace pads and wheel - and it works fine*** !
3. Check if rotor is bent ...

HTH and you get home safely !




*** allegedly ... it does in the video !

Ta, will give that a whirl later..!

 

[Pale Rider]

An occasional squirt of disc brake cleaner is worth applying.

It might stop the pads sticking again, once you have the present problem sorted.

Lots of makes of cleaner available.

I have a Muc-Off one from Halfords for about £5.

It's the same stuff motorcylists use, so it might be on that shelf, or you might pass a motorbike shop on the way home.

 

[User482]

That video is telling you 2 things to do.

1. Re-centralise the calliper - by slackening the bolts securing it to the frame; apply brake, tighten bolts while holding brake tight. You might need to do this a couple of times, apparently.
2. Re-Set the pistons - remove wheel, remove brake pads, use non-metal tool (old tyre lever) to push back the pistons as far as possible into their recesses. Replace pads and wheel - and it works fine*** !
3. Check if rotor is bent ...

HTH and you get home safely !




*** allegedly ... it does in the video !

The OP would seem to have cable discs - you can't re-set the pistons, though they can usually be adjusted with an allen key.

 

[Dec66]

The OP would seem to have cable discs - you can't re-set the pistons, though they can usually be adjusted with an allen key.

Yep, cable operated. Last of the big spenders, me

LBS tell me it's going to cost me more in repairs soon than a new bike. So, when the works shop window opens up in Jan...

 

[User482]

Yep, cable operated. Last of the big spenders, me

LBS tell me it's going to cost me more in repairs soon than a new bike. So, when the works shop window opens up in Jan...

If you do end up needing new brakes, chainreaction were selling basic Shimano hydraulics for less than £40 the pair. I have a set on my commuting bike and they're pretty decent.

 

[Scoosh]

The OP would seem to have cable discs - you can't re-set the pistons, though they can usually be adjusted with an allen key.

Aargh ! - forgot to say that the vid was referring to hydraulics … and my knowledge of discs is scant and only hydraulics at that … = again.

Thanks @User482

 

[mrandmrspoves]

Definitely reset the brake as described - but on most mechanical discs only one pad moves when you apply the brake so centering them is slightly different. First thing to do is wind the non moving pad in towards the disc. This is sometimes done by turning a knob on that side of the caliper in a clockwise direction - on other makes there will be an Allen key or a torx key recess instead of the knob. Now loosen the bolts that hold the calliper to the frame or the disc brake mount and then apply the brake fully on and while still squeezing it tightly, tighten the bolts that hold the calliper in place on the frame. Release the brake and then finally back off the non moving pad so that it is as near to the disc as possible without it rubbing when the wheel is spun. Now adjust the moving piston nearer to the disc if the brake feels slack, or back it off if it rubs when you spin the wheel. Finally check the feel of the brake again and if you are still unhappy with it, either loosen or tighten the cable until it feels right. Now your done!