wdmn

Hello,

I've recently started to have problems with my rear MAFAC dural forge cantilever brake. When the lever is pulled, only one of the two arms is moving.

I'm reluctant to replace the brake entirely mostly because my bike is a 70s Mercier and every part seems to be a different size than the standard parts available, so finding a cheap replacement could be difficult, but also because I like the look and feel of the brake.

So far I tried applying lubricant to the spring on the seized arm, and also took out the bolt to see if it was too tight or something (forgive my naivety about these things). I even tried loosening up the arm by gently tapping it up and down with a hammer (I was able to get it to move, but it doesn't seem to have done much good).

Is there anything I can do? I haven't been able to find any suggestions on the internet.

Thank you very much,


wdmn

Andrew R Stewart 

Initial thoughts are a seized pivot or broken spring. The spring would still let the arm pivot with finger pressure so suspect the pivot is tight. IIRC the arm spins on a set of red plastic bushings. These can be carefully pried out of the arm and then all cleaned up, lubed and reassembled with not much effort. Ebay or a local bike recycling org. would likely have replacements if things went south. Also make sure the cable is freely moving through the housing. the old housing didn't have plastic liner and rust can attack things. Andy.

wdmn

Thank you Andy.

I can move with my fingers (though it takes a lot of force), but it doesn't spring back afterwards.

How exactly do I get to the bushings? I have removed the bolt on that arm, under which there is a red plastic washer, but the arm doesn't seem to come off; is there something else holding it in place? Or do I have to use a bit more force to get it off? Or am I approaching this altogether in the wrong way?

Thanks again.

Andrew R Stewart 

Remove the bolt. Pull the arm off the pivot while rotating it, if you can detach the spring it helps. If it's the arm behind the front one take the ft one off first. A drop or two of penetrating oil on the bushing might help free it up. Andy.

wdmn

And if I can't get the arm off at all, does that mean it is corroded in place? I applied a lot of force and I just can't get it to budge (this is with the bolt out).

wdmn

So I removed the whole brake from the bike to get a better look.

I'm dealing with the top arm. I've removed the bolt, and released the spring, but cannot release the arm from the main bracket.

I'm attaching pictures of the front and back. It looks like maybe it needs to be released from the back as well?

FBinNY 

I suspect that the bushing is slightly compressed, possibly from over-tightening the mounting bolt (this wouldn't apply if it used to be fine, and now binds AND you didn't touch the pivot bolt in the meantime).

Canti's mostly use a similar basic design, where a bushing is slipped over the post, and the bolt is tightened hard against it. The bushing is very slightly longer than the thickness of the moving arm (and spring), so it allows movement with minimal axial play. With over tightening, the bushing mushrooms slightly getting shorter so the mounting bolt binds the arm.

If the bushing is shortened, the fix is to file the arms a bit thinner in the mounting area.

OTOH -

If you never tightened the mounting bolt, it' possible that it's simply a problem relating to dirt and corrosion, so start by removing the bolt and sliding the parts off to inspect, clean, oil and rebuild. These brakes are so simple that there's little potential to mess this job up.

wdmn

Thank you very much.

I never tighetned the bolt, and this problem has begun in the last few months. I have been having a lot of trouble with getting the parts apart so that I can clean them. I just gave it a generous dousing of a chain oil that is supposed to clean and lubricate, maybe that will unstick it enough I can separate the arm.

Andrew R Stewart 

So should I edit my edit? The brakes are what I (first mistakenly thought) racer center pulls. Not cantis. Not a big deal as the dissambly is much the same. But for some one who tries to be accurate (and when not feel's stupid) finding out that my editing wasn't needed...

In the end the fix if not the removal of the sticky arm and not simple dripping in lube and "working it" is to replace. Between EBay, the local "bike kitchen" (how I hate that reference) and various new repros of old designs replacement calipers are out there. Andy.

wdmn

Thank you Andy. It's me who feel's stupid, I suppose. I knew they were centre pull, but was lead to believe that they were also cantilever. Needless to say my knowledge of bikes is pretty much limited to riding them. Glad to know the accurate terms so I can use them going forward.

cheers,

wdmn

wdmn

Just thought I'd post this in case anyone else comes across the same problem.

I managed to get the arm off by heating the area with a propane torch for about 4 minutes. I had been worried because I thought (due to diagrams on the internet) that the bushings were vinyl. After looking at the brake a lot, I didn't think I saw any vinyl parts, and since I had nothing to loose as the brake would not come apart any other way, I gave it a shot.

Here's what it looked like when it came apart:





Cleaned it up with a brass wire brush, oiled it and put t back together. Now it works again!

Thanks for all of the advice.

rmfnla

I can understand wanting to keep things original but IM(not so)HO those MAFACs were the worst bicycle brakes ever made; stupid pad mount design and flex city!

The good news is, unlike your experience with other parts on your bike, they are a fairly standard size so they can be easily replaced. Lots of vintage parts out there, or you could upgrade them to something a bit more modern.

The other good news is whatever you replace them with will be better in almost every way...

Grand Bois

MAFACs are excellent brakes when adjusted properly.

WizardOfBoz

You have discovered the joy of figuring it out and fixing it yourself. Congratulations. Heat is a commonly used tool to release fixed bushings and stuck screws. Your Mafacs on a Mercier were a blast from the past for me: I worked in a bike shop in the 70s and set up a lot of similar Merciers.

rmfnla

Too squishy for my tastes...