U brake jams up / does not spring back

[Karsten4130]

Hello guys!
So I bought an used cheap bike for my wife (Mirra Blend) and the seatstay u-brake does not spring back after being pulled hard. The springs are well adjusted and in correct orientation. Cable tension releases too. Brake arms are not touching each other. Tried the stock Tekro brake as well as a AD-990, almost no difference. It seems too me, that the arms jam up on the mounts. I have no idea how that can happen and I've never seen that in over 20 years of BMX.
Any advice?

[paranoidmexican]

do the arms move freely when you take the brake cable off? you might have to take off the brakes and lightly sand/clean/grease up the mounts. make sure you clean the inside of the brake arms too.

[Karsten4130]

I now tried several brakes, sanded the mounts etc. What seemed to help finally was sanding the white powder coated rim which seemed really sticky, with residue of clear pads etc. . I think the problem was/is the kinematics of the SS brakes and the high friction between sticky pads and rim.

[smsabb]

Man I was just about to reply try cleaning the rim then I saw you discovered it was that .Back in the day they used to put tar on the rims of trials bikes for them to grab like that .