no motor?

My GF bought a used Trek Multitrack (it looks like an early steel diamond frame MTB that may even be old enough to have been made in the US) from a friend and was having problems with the front brakes. Before I took of the right front brake arm to lubricate it I noticed it wasn't retracting as well as the left front brake arm. The pin portion of the return spring wasn't engaged with any of the three possible holes, and removal of the right brake arm revealed the pin portion of the spring fitting in a black oval spacer with only a tiny portion emerging from the other side. There wasn't enough of the pin sticking out on the other side to insert into one of the three adjusting holes, and when I tried to put everything back together without the spacer the remaining parts were too loose to work in addition to the springs not fitting in their holes. Including the spacer allowed for the parts to fit together snugly, but not in a way that would allow both pin end of the return springs to be inserted in their proper holes. Here are some pictures of the parts in question.

An internet search revealed more confusion about the spring after I went to the Park Tool site and read down to the caliper attachment section where it mentions left and right hand springs. The winding on the spring in the picture above looks like it's going in the wrong direction - is it?

I've cleaned and adjusted both v brakes as well as center pull cantilever brakes many times before, but never had this much trouble. Do I have the correct parts here? How do I put everything back together so the brakes work properly?

no motor?

I wanted to thank however answered this question when I asked it in another section but I can't find the other thread. Their advice to just replace the brakes with something that was designed to actually work right (like the Tektro's I ended up with) was appreciated when I finally got the better parts in place and could go back to riding.

bikeman715

The item in your first photo is to adjust the spring tension of the brake . First of all put the brake back together as you found them . There might be 2 hole for the spring end to go into the brake 's arm , anyway put the end of it into that hole , put the adjusting nut ( your first photo ) on the other end of the spring with the cone shape onto the spring and into the arm , now put it back on the bike with the bolt , don't tighten the bolt fully yet , take the adjustable nut with a 13 mm cone wrench and move it back until you have added tension to the spring and the arm pull the brake pad away from the rim , once you get to this point ,tighten the mounting bolt to hold the adjustment . remove the cone wrench and the brake should work . If it too much tension on one side just back of the adjustment nut about 1/8- 1/4 turn .

FBinNY 

+1, the back plate is the spring adjustment cam, and replaces the 3 holes in the boss as the receiver of the spring's leg. If all is right the leg will not extend through the cam at all.

Assemble the brake, tighten the mounting bolt only enough to take up play, then use a cone wrench on the cam to tension the spring and balance it with the other so the arms are centered. Then tightening the bolt should keep everything in place.

no motor?

Thanks. I figured out how it was supposed to work, but the arm part of the spring wasn't long to go through both the adjusting nut and the holes on the fork. The brakes weren't working right to begin with, I suspect someone hadn't used the correct parts when they put the brakes on earlier. Those brakes got tossed in the trash, I'll probably replace the back brakes too later.

no motor?

Hmm, the rear brake spring leg is long enough to go through the hole on the boss on the fork. How did that happen?

FBinNY 

It's a shame, because unless you mistyped the above, you haven't figured out how they work at all. The spring is most definitely NOT supposed to extend through the cam and engage the holes in the boss. That would defeat the purpose of having the cam in the first place. If the spring did extend too far, either you have it upside down (the shorter leg goes to the cam), or someone substituted the springs for the wrong ones. But a spring with the leg too long is easily fixed with a bit of grinding.

no motor?

No, I didn't mistype the above. And it sounds like you're telling the one brake that actually worked on the bike wasn't installed correctly. And if what you're describing is right (and I'm not doubting you) it sounds a lot more complicated and harder to adjust when you're out riding than the Tektro brake I used to replace it. What possible benefit was there to the Dia Compe brakes besides additional service revenue to bike shops?

FBinNY 

I have brakes of a similar design, made by SunTour. The advantage is that the cam provides the ability to easily micro-adjust the centering, vs. the coarser adjustment of the 3 holes. Modern V-brakes replaced he cam with the small adjustment screws on either side, and later that design was applied to newer cantis also. It's not a question of better or worse, just a different design, but I've found the cam to offer a broader adjustment range in the event I couldn't find the right springs.

BTW- In over 20 years of using my cam-spring cantis I've never had to adjust them in the field. They hold adjustment with bulletptoof reliability. Let's hope your new brakes serve you that well.

Also note that some of the best modern Canti brakes have resurrected the cam design, with a twist (no pun). The spring is moved to the end of the post so the brakes can be at the base for improved rigidity, and the cam is directly under the mounting bolt. It's a good design, but only works if people know how to use it.

no motor?

Ah, that makes more sense. The new Tektros I installed have the small adjusting screws on each side and were really easy to install as well as adjust. These aren't too different from the v brakes on my Hardrock, and they only require an occasional fine tuning that's easily accomplished with the screwdriver part of a multi tool.