U brake
 

I have a 1988 jamis dakar sport, that I am converting to a commuter,. It has an IRD rotaty brake under the chainstays. It is a pita to adjust. will a bmx u brake work as a replacment, or should I just search for a shimano replacement. thanks

As long as it has the correct range of reach, should work fine.

I'm not familiar with the brake that you're talking about.

U-brakes require mounting studs that are in a different location than canty's. Under chain stay U-brakes tend not to be the easiest to adjust either.

To be honest, a 20 year old hardtail mountain bike frame might be cheaper to replace than brake hardware. For a commuter/beater bike I think that I'd be looking for something that has all conventional parts.

Tektro makes U-brakes. Shimano used to make them Even Campagnolo has made U-brakes. I have an old Peugeot mountain bike with a Campagnolo Euclid under the chain stays.

You shouldn't have any trouble at all finding parts for an '80s mountain bike. I never have.

BMX brakes should work. They use the same pivots and are used with 20 X 2" tires... same reach (approximately) as a mountain bike.
Talk to you LBS. They can likely order some very affordable U-Brakes. A few years ago I got two cheap sets to mount on an old 10 speed frame with BMX brake-plates - I don't remember the price but they were not expensive.

IIRC the tektro or dia-comp single sets (bmx) are under 20.

Roller-cam and U-brakes use the same stud mounting positions but I've never heard of rotary brakes.

A search turned up... http://www.mombat.org/Interloc.htm

"1988
- Developed the Rotary Brake
This half-U / half roller-cam brake was rated the highest in Mountain Bike Magazine's 1992 test of 22 MTB brakes in wet and dry stopping power."

But I can't tell from the photo on that page where the studs are.

Google u brakes, just did, many more sites and places to buy than I would of thought. Looks like quite a few people selling parts on ebay also.