Bicycle Mechanics - Brakes question: details inside
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01-12-10, 11:54 PM
I have a fairly cheap Marin Bolinas Ridge mountain bike that I'm trying to get in working order because I just bought two new wheels for it. The problem is that now that I've got the new wheels put together and ready to go, the brakes aren't working the way they were before.
They're the standard brakes that came with the bike--I believe they're aluminum linear-pull brakes, Shimano Altus levers. See several badly-lit pictures below. I've loosened and then re-tightened all the different components, and it seems that the left brake pull (left looking down from a seated position on the bike) lacks the kind of "spring action" that the right side still delivers. In other words, when the wheel is on and I press the brake lever, the left brake pad comes into contact with the wheel and then sticks, not springing back the way the other side does. I can't seem to figure out what's working on the right side that isn't working on the left. Any ideas? Should I just replace my brakes? I am trying to spend little to no money if possible. Apologies if this detail isn't enough/this question has been asked a million times before.
Also, good Bay Area bicycle mechanics who'd take a look for cheap much considered. Thanks!
01-13-10, 12:55 AM
No big deal, I had a similar problem with some other brakes of the same principle. On the back of the brakes, there is usually a small plate with holes in it. These mate a pin on the fork side. Depending on in which hole the pin sits after re-assembly, the brake arm will have a different angle. Just make sure that the pin sits in the same hole on each side and your brakes will look fine. Hope this helps.
.. On the back of the brakes, there is usually a small plate with holes in it. These mate a pin on the fork side.
Almost, but the other way around. The plate with the holes is on the fork, and the pin protrudes from the brake arm assembly.
.. Depending on in which hole the pin sits after re-assembly, the brake arm will have a different angle.... Sort of. Which hole you pick decides the return springs preload, which together with brake wire and brake pad adjustment determines the angle of the brake arm.
There's usually also a screw somewhere down by the base of the brake arm to fine-tune the return spring tension with. Some brakes have it on both sides, some only on one, on really low- end stuff it might be missing entirely.
If the lazy side has a screw, turn it in. If that doesn't help, turn the screw out, then move the pin one hole up and try again.
If the eager side has a screw, turn it out. If that doesn't help, turn the screw out, then move the pin one hole down and try again.
Repeat in different combos until you have rim clearance and the whatever brake return characteristics that you prefer. Some like it snappy, some like it mild.
... Just make sure that the pin sits in the same hole on each side....
No need for that, and doing it that way would cancel the possibility for individual adjustment of brake arm return, which is one of the key features of the design.
Functionally speaking you're OK as soon as both pads clear the rim when you let go of the lever. Having the pads contact the rim simultaneously is elegant, but doesn't really affect braking performance.
Some people never bother resetting the anchor point, but will simply unhook the lazy spring from the brake arm, bend it outwards and then hook it back up again.
01-13-10, 02:37 AM
hm, shoulda read the manual first ;)
01-13-10, 02:48 AM
In your picture the left side arm isn't returning at all so there's something obviously wrong. It is one of four things. Either the pin isn't in the right spot as described above, the pin has fallen out and gotten lost, the tension spring is broken or the pivot bushing is rusted and jammed solid.
If the pin in the plate solutions so well explained above don't do it then check the following.
Somethign that I've seen before is that the alignment pin mentioned above gets loose and falls out. If you have no pin on the left arm like there is on the right that fits into the little plate with one or three holes then you have no real option but to go and buy a new brake set. Most of us could cobble something out of our spares but I gather you don't have that option.
Another other option is that the spring arm has broken. I've seen that problem in the past too. Move both the arms and you'll see how the wire spring arm on the right side works and then see if it's working on the left side. If it's limp and won't tension the arm and it wasn't the plate pin from above then the end of the spring wire has broken. Take the arm apart and check that it didn't just slip past the shoe that is controlled by the screw mentioned above. This can happen quite often as well depending on the design if things got loose at some point. When you open up that area it should be pretty obvious if the wire snapped off or just jumped over the stop. If it's broken again there's no real option but to replace the brake set. If needed compare the right side to the left.
If the pins are both there and you can see that the springs are working or trying to work but the arm still isn't moving then it may be because the bushing that the arm pivots on is rusty inside and it's just plain jammed up. If that's the case then you need to pull apart the pivot at the hinge to clean things out and re-grease the pivot. Note that the brake arm does NOT pivot on the pin of the fork. Instead there's a bushing in the pivot assembly of the brake arm that locks in place when you bolt the arm onto the fork. The arm itself pivots on that bushing when you apply the brakes. The bushing has some really oddball keyed washers on one side or the other that press on to hold things together. You'll need to pry those off to allow the bushing itself to be pushed out. Because the left side bushing by this time has been found to be jammed I'd take apart the right side so you can see how it all works. Then attack the left side. If you're having trouble dealing with all the little parts, and there's lots of them, then take some digital pics so you can see how it comes apart to help with putting it together. Once apart if you see rust sand it off back to bare metal. Same for the inside of the arm bushing. If it turns out to be gunked up dried grease then use some solvent to clean things up. Usually it's rust or corrosion though.
I'm betting on a missing alignment pin or that the spring jumped over the tab on the stop plate.
01-13-10, 12:40 PM
Thanks for these suggestions...I'm at work right now, but when I get home I'll take a look. I believe my problem is one of the second two you listed; either the tension spring is broken or the pivot bushing is jammed. I did experiment with the three holes and adjusting in various ways to fix the problem, but that didn't seem to work. I'll probably be back on later with additional questions/success stories. Thanks again to everyone who posted a reply.
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