Sticking Back Brake

[mgarl10024]

Hi all,

I've noticed that my back rim brake seems to be very sticky. When applied, 1 in 4 times either of the pads wont release. If I give them a little nudge with my finger, they spring out, so I don't think it's a spring issue.
Around the rim there is a groove (perhaps a wear marker) which is recessed from the rest of the rim, and I can see that the brake pad has worn with a little bit sticking out to match this groove. My guess is that the brake pad 'slots' in and gets stuck.
I can move the brake pad ever so slightly so that it doesn't slot in, or I could try to file this bit down. Is this something that many of you get? Strikes me that this must be a common problem? What do you do?

Thanks,

MG

 

[HLaB]

Most likely its a cable snag. If thats the case the only real cure is a new brake cable. I've also found in my less well maintained V'brakes dis-assembling them and greasing the mounts and increasing the tension (shifting the brake spring up) helps but it'd be better just to maintain things more regularly

 

[Greenflash]

Hi. The symptom you describe could be down to many factors. However, you may be on the right track in thinking the pads are getting stuck in the ridge as you describe. Try gently sanding the ridges on the pads flat. Take off the pads and rub on abrasive paper on a flat surface, rather than by trying to do it "in situ". Be careful to align the pads properly when refitting. Pads "overshooting" the rim often cause a similar problem.

 

[mgarl10024]

Hi HLaB and Greenflash,

Thank you both for your excellent suggestions.

@HLaB
I'll be sure to keep a closer look at the cables and mounts, but I don't think that this is my issue here. The bike is still relatively new, and all of the cables appear to be working fine. The issue is more than the brake blocks are getting stuck in the groove/ridge in the rim. It's almost (and I'm exaggerating here) like the brake pad has worn to the shape of a jigsaw piece that is plugging into the rim.

@Greenflash
Thanks for this suggestion. I had tried gently sanding the pads "in situ" with the wheel out but had got nowhere. I tried as you suggested - taking the offending pads out and gently running them along some fine sandpaper - and it worked a treat. It wore down the little lump that was getting stuck in the ridge, and I knew it was working as only a very thin (pencil width) line was being left on the sandpaper - when this widened to a full brake width I knew the job was done. Refitted, and (as far as I can tell), no sticking. Had to do the front ones too, and it'll be tested on tomorrow's commute.

The bike is around 4mths old (I've done about 750 miles). The pads still seemed to have a lot of life left in them, so I am guessing that this problem will keep occurring (in perhaps another 750 miles) - so I'm imagining that I'll need to repeat this process about three times before the pads need replacing.
Looking at my GF's bike (a different manufacturer entirely) she has the same groove in the rim and I'm guessing would also get the same issue when she's clocked up a similar number of miles.
Though I can't believe that everyone with these brakes has to do this, otherwise I would imagine seeing this commonly over the Internet? Do many of you get this?

Thanks,

MG

 

[Greenflash]

Hi MG,

Hope the immediate problem with your brakes is sorted, since you have now established that the pad sticking into the groove is the issue, here's some further advice...

First, the groove in your rim. That's not a design feature. That's when you picked up a bit of crud (probably containing sand, glass or gravel) and scored a neat scratch into the soft aluminium alloy of the rim.
This isn't usually a big deal, but if its interfering with the safe operation of the brakes you will need to keep an eye on it. Just an occasional little joggle to put the block surface into a slightly different position should discourage another reciprocating ridge from forming. There are ways of resurfacing the rims, but not really worth it since another score will appear very quickly after use.

I guess that you're using V-brakes and that the blocks are set quite close to the rim. This set up encourages crud to gather around the blocks. Try backing the blocks away from the rim, make sure you do this within the safe tolerances of effective braking.
Many cyclo cross riders prefer the older (IMO better) centre pull cantilever set up because the blocks can be fixed a good distance from the rim with about 1cm of travel before they contact. Worth considering if you ever have to replace your brake system.

Finally, and I don't mean to sound patronising here, keep your brakes and rims clean. Use an old toothbrush to get bits of rubber, muck etc off the blocks. I use a cloth with a dab of Dettol (contains isopropyl alcohol) to wipe around rim and then rinse off with a hose or whatever. And it smells lovely!

 

[2Loose]

Hi MG,

Hope the immediate problem with your brakes is sorted, since you have now established that the pad sticking into the groove is the issue, here's some further advice...

First, the groove in your rim. That's not a design feature.

Actually, it almost definitely is. Example

My month old Mavics have a groove in the rim which is a wear indicator. When the groove is no longer there, my rims will have been sanded down by brakes &\or grit so far that they need replacing.

 

[mgarl10024]

First, the groove in your rim. That's not a design feature.

Actually, it almost definitely is. Example

Hi Both,

I think it's supposed to be there. Here's a pic of the bike brand new - My Bike

Thanks,

MG

 

[PpPete]

Don't know about your Marin, but I've had to replace a cable and pads on a low-end Giant hybrid that was only weeks old (albeit with a good few hundred miles on it).
The original pads wore out very quickly, and galvanised cables were giving just too much friction for the pads to come off the rim reliably. Tried moving the spring up to the next hole but that wasn't enough so I replaced inner and outer cable on back brake with better quality (lined outer, stainless inner) and problem went away.

Yes I know it should really have gone back to the LBS where it came from, but we were on tour several hundred miles away from home, and needed to get it sorted ASAP

I really don't think it's anything to do with that groove.

 

[Greenflash]

Hi,
Sorry, should have phrased that better...the groove may not be a design feature...etc. but on your rim it is! Wear indicator grooves are usually designed with a profile that prevents them from "snagging" the block. Try the occasional joggle, that should sort it.