I post this at the Mech section.. but got no responds, perhaps here would be better. Recently I replace the brake pads on Tektro R540 (dual-pivot sidepull brake caliper) for my road bike. I followed the instructions on Zinn's road bike maintenance book, but I have some problems with the rear brake tensions.

First I tried adjusting the barrel adjuster (82), but since the new brake pads are thicker than the old used ones. I loosen the cable fixing bolt (70) to readjust the tension. After everything seems ok, I tighten the cable fixing bolt. But then once I hit the brake, the tension became loose again, and I can see the brake is almost rubbing the rim until I use my hand to open the brakes myself, (as if the spring doesn't work). I try this a couple times and still couldn't solve the problem.

I bought this bike last year, and I think the spring should still be good. The front brake is still pretty good too. I checked the cable, doesn't seems to be damaged neither. I am not sure what else to check. Please let me know you know what the problem might be and how I could fix it. I would like to try to fix this myself before I go ask help at the LBS. Thanks in advanced.

Without the cable attached, if you squeeze the calipers closed, do they return to a fully open position? If not I'd say you have an issue with the spring.

It could be crud in the cable housing.

I've had sweat evaporates accumulate in the cable housing but they tend to render the brake totally inoperative.

Or you could have a burr on the cable housing at the entrance or the exit that's restricting the free movement of your cable.

If you were to remove the wheel and the cable from the brake, when you squeeze the calipers together are they "pushing" back against you and snapping back into position?

Did you lube the pivots well with Tri-Flo or a silicon lube?

Well???

ok, I just tested it. without the cable, the brake opened just a little (not fully) after I pushed them against the wheel. Let me take the rear brake out to see if I can find the pivot point the clean/lube it.

and it improve slightly.. but not completely, i will bring the bike in to the bike shop and check.. otherwise.. i guess i will replace the Tektro R540 with the 105 brake set... but sigh. that is costly. for that i just got the SwissStop green pad.