Single Pivot Side Pull Caliper Help
 

Hello,

So I've assembled a bike a friend bought but I can't seem to get the brakes to work properly. They are unbranded generic side pull calipers where everything is adjusted with a bolt. It's got two bolts in the front and one in the back and two more to adjust pad placement.

The issue I'm having (I've basically tried every permutation of this) is the front caliper only pulls one side. I figured it may be because the bolts are too tight so I loosen them a bit: no help. What does help is if I give the cable more slack but then when it does clinch together, it's not clinching hard enough to truly stop the wheel. Tightening the cable will again cause only one side of the caliper to pull, thereby uncentering it.

Ideas?

have you tried some grease on the pivoting area? might be just that they're terrible brakes.

Put a wrench on the back nut and another on one of the front nuts (whether inner or outer depends on which way you need to rotate the caliper to center it), and turn both at the same time to center the caliper. Squeeze the lever a couple time to test, and re-adjust as needed.

Very often a thin wrench is needed to hold the inner front nut while doing this. Park, Weinmann, Dia-Compe, and others made thin wrenches for this purpose.

First is that I think you mean nuts, not bolts. Some might quibble on this but knowing how to talk about this stuff is part of learning the stuff.

The spring crosses through the center bolt's "hub" via a slot cut in the hub. It is this portion of the spring, the straight section that is in the hub's slot, that controls which end of the spring (and thus which caliper arm) is pushed away from the rim. So rotating this hub/center section of the center bolt/spring and keeping it from rotating back is key to "centering the pads". The center bolt's backing nut (the nut that holds the caliper onto the frame/fork) needs to be loosened, the center bolt/spring rotated so both pads are free of the rim, and this nut then tightened to trap the spring's arrangement.

Note that the cable casing also acts as a spring if not well routed or too short. A casing that can shift along the frame (as in a rear brake) with handle bar swing will cause the caliper to get pulled off center in time. Using a zip tie around the casing to keep it from sliding about helps reduce this.

If the center bolt's hub and the slot containing the spring is poorly made the spring can not be securely held and the spring will rock about within the slot. A sign of badly made or damaged brakes. Andy

Having thin open ended brake wrenches similar to cone wrenches but smaller makes adjusting brakes much easier than using needle nose pliers which is what you are probably using now.

Lots of cheap sidepulls don't have something to grab in front to center so this method often needs to be used.

​​​​​​Dave Moulton's Blog - Dave Moulton's Bike Blog - Centering side-pull brakes