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Rear disk (mechanical) brake lock up

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Rear disk (mechanical) brake lock up

Old 01-10-19, 08:00 AM
  #1  
RidingMatthew 
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Rear disk (mechanical) brake lock up

So it happened again... I rode this morning and it was 21F plus wind chill. I noticed about mid point (in my 10.5 mile one way ride) that rear brake was not releasing. I could feel the drag. This is the second time that it has slowed me down. Last time it completely stopped the rear wheel and would not release at all. So not only was I fighting headwinds my brake was slowing me down.

I am not sure what I need to do about the brakes. 2018 Salsa Journeyman 650b with mechanical disk brakes. Why would the brakes stay applied? The lever is in the right position (as if it was released)

could it be the pads bond or freezing to the disk or what would cause the brake to hold and not come away from rotor surface.

advice? help?
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Old 01-10-19, 08:03 AM
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Piston(s) is/are sticking, most likely. The caliper arm (and therefore the cable) only pushes them in-- the little spring between the pads is what pushes them back apart.
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Old 01-10-19, 08:19 AM
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So you can use the rotors as hand warmers???

I'd take the bike out in the cold when I had time to replicate the problem then head somewhere and tear into it.
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Old 01-10-19, 08:26 AM
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@DrIsotope that sounds logical but how do i check/ fix it? Is it fixable or should I look for new brake calipers?
@nomadmax i probably could have used the rotors as hand warmers. I am worried I am using up my pads for no reason. grr.
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Old 01-10-19, 08:27 AM
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I would see this all the time in Germany with cable-actuated items (front/rear mechs and disk brakes) if the temps were low enough and the lubricant would go through phase transition or snow/ice would build up on the cables.

This is why the Magura hydro rim brakes were rolled out from motorbikes to bicycles in the first place before discs before were really considered on commuter bikes.
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Old 01-10-19, 08:37 AM
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@acidfast7 are you saying the ice buildup is in the cable housing? It was dry this morning just cold with some strong winds.
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Old 01-10-19, 08:54 AM
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Originally Posted by RidingMatthew View Post
@acidfast7 are you saying the ice buildup is in the cable housing? It was dry this morning just cold with some strong winds.
Seen it happen. Also seen mineral oil-power hydraulics freeze. It's much better to use DOT-powered brake fluid systems as the freezing point is lower by about 40C or so depending on mositure ingress.
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Old 01-10-19, 09:03 AM
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I had this happen to before as well, even in dry conditions. There is moisture in the housing and when the brakes are applied they stay stuck. Fortunately the few times it's happened to me it released enough for the wheel to spin, but I'd lose the rear breaks for the rest of the ride.

The angle at which cable attaches to the caliper is to blame, so gravity just pulls whatever water there is there and pools it by the lowest point in the cable.

Often after a wet ride or after spraying the bike down I have to hang it to drain all the water out of the housing. This seems to help.

If it happens again you can probably manually pull apart the caliper and just not use it for the rest of the ride.
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Old 01-10-19, 09:14 AM
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Originally Posted by mcours2006 View Post
Often after a wet ride or after spraying the bike down I have to hang it to drain all the water out of the housing. This seems to help
upside down? this my 1st winter w mech disc brakes
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Old 01-10-19, 09:19 AM
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Originally Posted by RidingMatthew View Post
@acidfast7 are you saying the ice buildup is in the cable housing? It was dry this morning just cold with some strong winds.
Your lubricants aren't freezing. But they can lose viscosity due to cold. That can cause a sluggish response. Also just because it's dry today does not mean there wasn't moisture on the parts. There could have been condensation on the parts from inside your house that froze when you took it outside. (Thinking glasses fogging up on a cold day when you walk out).

However, what you describe sounds worse than normal behavior. Is the front acting weird too? If not, I'd say to get the back released with force and just try to use the fronts on the way home.

Do you store the bike inside all day? Once it's warmed up inside see if the rear brakes work fine again. If they don't it might not be a cold problem. It might just be a coincidence that the problem happened today. The cable may have gotten stuck. The spring in the caliper may have lost it's 'spring'. There are all kinds of things that could be wrong. If the brake acts the same way once it's warmed up, it's something like that. If it works fine when its' warmed up, it's some sort of moisture that shouldn't be in there.

The pads are NOT sticking to the rotors because the rotors are warm if there is brake dragging, even on a cold day.
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Old 01-10-19, 09:47 AM
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@acidfast7 they are mechanical so it is not a brake fluid issue.

@mcours2006 I think that this is it. "The angle at which cable attaches to the caliper is to blame, so gravity just pulls whatever water there is there and pools it by the lowest point in the cable." i am riding year round and trying to stay away from puddles but maybe there is water in there.

@Skipjacks it sounds like you might be right on the spot with this. It is not the front. It is only the rear that have done this to me. It must be moisture in the cable housing and 20F with wind-chill is making it freeze up. I am confused as to why the brake lever goes back to normal spot though.

The bike is stored in a section of my garage so it is warmer than outside by a little bit. It seems to have happened when going downhill in the cold at high rates of speed 20+mph so far. It worked for over half of the ride. this happened in the middle of the ride. The bike is in the parking garage under my building all day so warmer than outside in the elements for sure. I think it released as I rode this morning. The other time it was tight enough that the rear wheel stopped but it spun freely after my wife picked me up and the bike was in the back of the van.

@rumrunn6 this is my first winter with mechanical disks as well.
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Old 01-10-19, 10:28 AM
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Originally Posted by RidingMatthew View Post
@acidfast7 they are mechanical so it is not a brake fluid issue.
I know. I recommend you change to hydros and run DOT fluid.

If you stay with mechanicals, it's probably fluid in the cable line or fluid frozen in the lever/actuator.

Last edited by acidfast7; 01-10-19 at 10:49 AM.
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Old 01-10-19, 10:31 AM
  #13  
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Originally Posted by acidfast7 View Post
I know. I recommend you change to hydros and run DOT fluid.
that is on the radar but I just bought the bike in august. I am not sure CFO would be okay with that just yet.
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Old 01-10-19, 10:50 AM
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Originally Posted by RidingMatthew View Post
that is on the radar but I just bought the bike in august. I am not sure CFO would be okay with that just yet.
Sorry man, made an edit while you responded.
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Old 01-10-19, 10:51 AM
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Originally Posted by mcours2006 View Post
I had this happen to before as well, even in dry conditions. There is moisture in the housing and when the brakes are applied they stay stuck. Fortunately the few times it's happened to me it released enough for the wheel to spin, but I'd lose the rear breaks for the rest of the ride.

The angle at which cable attaches to the caliper is to blame, so gravity just pulls whatever water there is there and pools it by the lowest point in the cable.

Often after a wet ride or after spraying the bike down I have to hang it to drain all the water out of the housing. This seems to help.

If it happens again you can probably manually pull apart the caliper and just not use it for the rest of the ride.
Everything here, seconded. Exactly. I have even hung the bike in several orientations to clear the water, each time also spraying WD 40 down the cable housings as well.
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Old 01-10-19, 11:14 AM
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Originally Posted by rumrunn6 View Post
upside down? this my 1st winter w mech disc brakes
Uh, more like on its hind legs, so to speak. I hang it on hook from the ceiling by the front wheel.
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Old 01-10-19, 11:16 AM
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This is one reason I will eventually go with hydraulic disc.
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Old 01-10-19, 11:23 AM
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Cable binding in the housing? (covered above) the little pad spreading spring broke? new ones come with new pads , bike shop may have spares remaining from pad changing ..

[you need to know what specific brake brand and model it is]

Done any maintenance? Like Taken off the caliper , removed the pads, and then, sprayed in some lube (Like WD 40) ?





....
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Old 01-10-19, 12:11 PM
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@fietsbob the brakes are Promax DSK-330r at mount 160mm salsa guide i only have 1540 miles on the bike. It is/ was brand new in Aug 2018
i have not done any maintenance on it either.
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Old 01-10-19, 12:15 PM
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Originally Posted by RidingMatthew View Post
@fietsbob the brakes are Promax DSK-330r
wow, new bike! I have Promax 310s
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Old 01-10-19, 12:15 PM
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Originally Posted by mcours2006 View Post
Uh, more like on its hind legs, so to speak. I hang it on hook from the ceiling by the front wheel.
I shud be able to handle that! thanks!
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Old 01-10-19, 12:33 PM
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Promax DSK-330r
Promax a price conscious builder's parts pick choice, to keep bike price attractive


i have not done any maintenance on it either.
I'd say its overdue..
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Old 01-10-19, 01:52 PM
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Originally Posted by fietsbob View Post
Promax a price conscious builder's parts pick choice, to keep bike price attractive
I'd say its overdue..
i am sure that Promax is price conscious choice but at least i can upgrade it later. and i guess i will have to look into doing some maintenance on the rear caliper.
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Old 01-10-19, 02:43 PM
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Originally Posted by rumrunn6 View Post
wow, new bike! I have Promax 310s
yes it is pretty new and that is what boggles my mind about the brakes. I had 2 broken spokes early on and the bike shop rebuilt the wheel with what they say are stronger spokes. I have not broken one since. I appreciated them fixing it up.
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Old 01-10-19, 02:48 PM
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Originally Posted by RidingMatthew View Post
yes it is pretty new and that is what boggles my mind about the brakes. I had 2 broken spokes early on and the bike shop rebuilt the wheel with what they say are stronger spokes. I have not broken one since. I appreciated them fixing it up.
have them do some maintenance on the brake & cable. I've been thinking about doing the same. I bought mine used so mine are a big question mark
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