efiste2

HI .......I am trying to sort out the brakes on my sons bike, in his wisdom he took them off his BMX bike, but I have made him put them back, however we cant seem to attach the caliper arms to the frame and keeping the sprung so that caliper arm pulls away from the rim when the brake is released.......the bit we are struggling with is shown in the pic below ANY help would be most appreciated, also am I correct in thinking that the springs are handed ie a left spring and a right spring.

bikeman715

You have the setup backward . Try revering the the brake arms ,what you have in the photo go to the left side of the bike and what on left go to the right . And the nut in the front of the photo go to the back and is held in place by the frame once all the parts are put back on right. The nut is use to adjust the tension in the spring to bring back the pad from the rim . The brakepad is to high in the front which can lead to a blowout .

efiste2

Sorry I should have mentioned the bike is upside down so the lever arms are on the right way round as far as I can see....and the pads are not set yet....

Airburst

What you have there is a U-brake. There should be holes in the brake arms that take one end of each spring. That side should face the spring, obviously. If the springs are wound in opposite directions (i.e. one clockwise, the other anticlockwise) then they're handed, if not, they're universal. I've seen both.

Adjusting the spring tension on a U-brake is a little tricky, but basically, that hexagonal spring block is turned with a wrench* to set the spring tension, and is then clamped to the end of the brake stud on the frame by the mounting bolt (the allen-headed one) so it can't rotate. You have to hold the spring block in place with the wrench as you tighten the mounting bolt, as it will rotate with the bolt if you don't.

The spring tension has to be balanced reasonably well so that both brake arms pull away from the rim. If one is set higher than the other, only that side will pull away, leaving the other brake pad dragging on the rim.

*I know it's called a spanner here, but apparently a spanner is a different tool in the US, so I've taken to calling it a wrench on here to avoid confusion.

Monster Pete

What bikeman means is that the brakes are assembled back to front. The large 'nut' should go on first, against the frame, followed by the spring, then the brake arm.

Airburst

It may not, a lot of BMX U-brakes have the spring block on top of the brake the way the picture shows. I believe I've seen that particular model before, actually, and it does.

vredstein

As set up in this picture, it looks like if you just loosening the allen bolt a bit will allow the 6- sided nut to turn. If you turn this nut counter clockwise, you are increasing the spring tension and moving the brake pad away from the rim. Of course, once you let go of the wrench it will spring right back to the neutral position. But if you turned the nut counter clockwise , held that tension in place by holding the wrench in place, and tighten the allen bolt down with your other hand, that spring tension would be locked in.

For setup, your first step is to loosen the allen bolt. Don't remove it, just loosen it one full turn. Then turn the nut counterclockwise 1/6 of a turn and as I said, hold that position with the wrench while tighting down the allen bolt.
The other brake arm should be the opposite-you turn the nut clockwise to increase spring tension. Perform the same steps with this other arm.
Now operate the brake and see if both pads hit the rim at the same time. If not, increase tension on the side that hits first.

fietsbob

^^^ this .. the hex, turned, creates the spring counter force, the allen bolt holds the adjustment.
Hex on one side turn CW , the other CCW.

Greyryder

I thought brakeless freestyle was a fad, when it first showed up back in the 90s. Now, I think it's an epidemic. I'm glad I always leaned more towards race bikes.

Just went looking at the U Brakes over at Dan's Comp, and a lot of them are made that way. They are indeed assembled correctly.

Listen to this man, he knows of what he speaks.

efiste2

Thanks for all the help Guys, we sorted it....turned out the bolt holdding the spring tensioner nut was too short so it was compressing the spring too much and not allowing it turn compress and un-compress if that makes sense, once we sussed that it was simple.......once again thanks for all the help. much appreciated!!!!

michaelscycles

Glad you got it sorted out. If I saw this sooner I might have been more help. Most of the answers you got are from people that must not have a lot of experience with BMX. Your brakes look to be Odyssey Evo brakes. They are great quality brakes, but can be a little more difficult to set up then most. You were correct that there are left and right springs. If they get mixed up it can be hard to tell which one is which. At least you have a 50-50 chance of getting it right.

dabro343

Just a stupid question why would you want to turn one side ccw and the other side cw? I talked to a guy at a bike shop and he told me to turn them so they both pull away from the rim? And now i am finding out that one needs to go ccw and the other is cw.

dabac

Think about it. The springs adjust how hard the brake arms pull away from the rim. But as the brake arms sits on opposite side of the rims, you need to turn them in opposite directions if you want to increase the clearance force.

Pushing the right side brake pad to the right increases clearance, but pushing the left side brake pad to the right decreases clearance.
So you need different directions to get the same result.