Originally Posted by surreal

You wanna know about that funky rear brake? It's a U-Brake, and it's the most awesome brake ever. The mb-5 may've been the second-to-crumbiest Bridgestone MTB ever, but it's still got rockin' geometry. If it has a chainstay mounted u-brake, that'd make it a 1988 model. These have about as short a wheelbase as horizontal-toptube mtbs ever had, but it's still gotta be at least 420mm at the chainstays.

I tried to not get into the whole bulldog/880-style "bmx" caliper discussion, but those are the worst brakes ever. With some fiddling, you can set them up to stop a wheel, but they'll never perform very well, and the feel at the lever is utterly disgusting. Avoid. You can't be sure they'd even do the trick for this application, anyway, unless you do some careful measurements. Get a coaster or a drum or something... or get some lockjaws by mr. tick. Which is what you'd really need for this l'il experiment, but if $100 seems like a lot for a cool mtb like an mb-5, then $75 for some bolt-on canti bosses will probably give you fits.