U Brakes Help/Suggestions

[deliquium]

I have a 1992 GT Karakoram frame and forks which are now disguised as a shopping bike (Vibrant semi fluo orange with black LSD/Pollock inspired paint splatter notwithstanding). It's great. I love it to look at and ride. It takes loads with ease. Nobody is going to nick it outside shops (in North Wales anyway)

BUT, it's got an original Deore DX U Brake on the seat stays (thankfully not the chainstays). It's not very good at retardation. It feels awful and needs a lot of hand pressure to make it work. Is it because I'm using modern V brake levers (because having fitted a pair of new 21st C. Deore V brakes to the front)? All cables replaced and U Brake pivots lubed/greased + new not sure about brake blocks.

Are there any better replacements? Or any other suggestions?

Click on the pic for a larger version

[531colin]

Put the old lever back on?

[deliquium]

Put the old lever back on?

I bought the frame and forks BARE inc rear DX U brake and plastic cable twizzle bit to cross the wires around the seat tube

Good price - nice seller of this parish - great/odd/lovely/bizarre/comfortable

[gaz]

Some Shimano V brake levers have two cable settings, one for V, one for canti. It may be worth taking a look at the tech docs for your levers.

Edit: e.g. BRM590: http://techdocs.shimano.com/media/techd ... 671232.pdf

[531colin]

I imagine when made they were canti. front and U brake rear, so a U brake is similar cable pull to a canti, rather than similar to a V brake..

I guess you need a flat-bar canti lever to get the best out of the brake.....unless there is a "reverse travel agent"....?

Gaz. has a good idea, as ever!

[Redvee]

Have you over tightened the mounting bolts? Undo them 1/2 a turn maybe.

[LWaB]

Absolutely need a shorter cable pull than a V-brake lever provides.

[Brucey]

yes you definitely need a shorter pull at the lever than is generated by a V-brake-only lever. Gaz's suggestion of a dual pull lever is a good one because you will at least be able to have a matched pair of levers that way.

BTW the MA of the brake will vary with the setup and geometry. In no particular order;

1) guide friction. If the seat tube guides are draggy this will make the brake work less well.
2) brake pad compound; you may well find that a softer compound gives a higher friction coefficient.
3) straddle geometry ; IIRC the MA is highest when the straddle crosses itself after the seat tube
4) brake arm geometry; sometimes (a photo would help to check this) with a crossed straddle cable, the higher the arms are, the higher the MA.

The last point is worth a little thought; using slimmer brake blocks should raise the arms; maybe 'V' type blocks would be a good choice. IIRC the original brake blocks with this brake were kind of thick, kind of hard, and only got harder with time.

cheers

[deliquium]

Thanks all for your replies. I'm sure I have a left hand cantilever compatible brake lever somewhere in the bike cave. And yes, the pads are awful - hard, short, thick and awful. Mind you, the cable routing isn't pretty either.

I also recall some Avid levers that had adjustments so as to run canti OR V brakes??

Am also wondering how much paint would be affected if I were to saw off the U brake bosses and have V brake bosses brazed on. There's no way I want to have the whole frame painted - it would be impossible to recreate the "GT Inferno" random "dribble and splatter" effect

[Steveo2020]

I had a replacement canti boss grazed on to my bike. The area of paint damage was quite small - prob 3 or 4 inches and I just painted it black (original is green). I don't think you notice too much.
Cheers