I am currently working on a Diamond back Apex with a rear U brake And I have managed to screw it up. Since this was a sale bike for the Bike Exchange I took it apart for cleaning and thought I should pull the U brake even though it was working fine. In doing so The drive side arm would not come off the stud. Also the internal spring came out. Nothing I tried seemed to work in putting it back together. I tried inserting the spring with the short end in and out , Used the hex wrench to twist the spring. When I replaced the plastic cap and bolt the spring would not engage and wind up the arm. Then I pulled the other arm to see if I had done something wrong an managed to break the plastic cap , making it unusable.

This is a beautiful bike which saw little use in its 30 plus years and I would hate to think I have ruined it over a plastic cap. I looked on E bay and there are lots of u brakes sold for BMX bikes that look like they might work .

Has anyone else gotten themselves into this fix and if so how did you work around it. Also, Is there a tutorial on how to remove and replace these brakes. This is the second u brake I have worked on. The first , a Yellow Diamond back Assent I did a few weeks ago , went back together without incident. We have tons of brakes of other types in the shop parts bins but no U brakes.

Under stay u brakes are about the most frustrating rim brakes made. Bad location for contamination from chain. Water rusts the post easily, Hands get scraped by the rings when working on them. Poor cable routing requirements. And a fix for a problem that had a far simpler solution.

Thankfully they didn't last long on MtBs and the 20" bikes with them generally don't see the weather and do have more space between the brake and the ring. Andy

This image, from Retro bike, might help. I understand why people don't like them, but I've had them on a few bikes without too many problems. These Deore's seem to work okay. Is it the "boss cap" you broke? It it, by chance, the same model of brakes as this? If so, I actually have an extra boss cap.

Only thing is I live in Canada and it could take the mail a long time to get to you. PM me and I'll mail it to you if you could use it.

And , yes, I think some BMX models can serve as replacements. At least I did use a BMX replacement on one bike I had, but that was a long time ago, and I don't remember the details.

Don't know if this will help?
Brake Model#?

Famous mechanics quote: "If it ain't broke, fix it til it is"

I went in to the shop today and they actually have a box of U brakes and parts. I found a Tecktro brake and installed it and it looks like it will work. It is a little less beefy than the Shimano part but should do for this build as the bike is set up as a street/ beach cruiser. The end of the lever arm is REALY close to the chainring but does clear it. I will post pics when it is finished.

Thanks for the comments folks. It is nice to know that others have information to share.

Sounds like you got it working. It is very common though to have a u-brake post slightly mushroomed with the brake arm stuck. Any of the models that use an open end wrench for the spring adjustment will have been over-tightened at some point to keep the spring from slipping.