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 Post subject: Blinkin U brakes....!!!
PostPosted: Tue Apr 24, 2007 10:45 pm 
Old School Grand Master
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Joined: Tue Jul 05, 2005 3:14 pm
Posts: 13403
Location: Warwick
Anyone else U-brake-friendly?

I cant seem to get them to balance properly - Ie. one arm alsways seems majorly further than the other from the rim.

The only way I got around it before on the old trimble was to put more spacers in on one brake arm side so that the brake shoes kinda touched the rim evenly....even so this always seemed to move the rim sideways under heavy pressure when braking...

Anyone any experience with these rubbish contraptions?


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 Post subject:
PostPosted: Tue Apr 24, 2007 10:55 pm 
B.o.T.M. Winner / Feature Bike
B.o.T.M. Winner / Feature Bike
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Joined: Tue Dec 13, 2005 3:26 pm
Posts: 6191
Location: Tilting at windmills and shouting at the rain.
seem to remember that there is an allen key adjuster on the side, but here's some info from Mr S Brown:

"U-Brakes"

A form of cantilever brake that works like a centerpull caliper. The "L"-shaped arms cross over above the tire, so the left brake shoe is operated by the right side of the transverse cable. A U-brake uses studs that are above the rim, rather than below the it, as with conventional cantilevers. They use the same type and placement of studs as rollercam brakes do.
In 1986-88 there was a fad for equipping mountain bikes with U-brakes mounted underneath the chain stays. This provided a nice clean look to the seat stay area of the bicycle, and provided a somewhat simpler cable routing. In addition, since the chain stays are larger and more rigid than typical seat stays, the "problem" of flexing of the studs under load was reduced. Conventional cantileves cannot be mounted on the chainstays, because the cantilevers would get in the way of the cranks.

Although U-brakes were cool looking and powerful, the fad died quite abruptly when people actually started using the bikes that were sold with chainstay-mounted U-brakes. They had several serious drawbacks:


The inaccessible location made it very difficult to service or adjust the brakes.

They complicated the process of wheel removal.

They tended to get clogged with mud.

Due to the high-mounted studs, if you didn't monitor the brake shoe wear carefully, as they would wear, they would hit higher and higher on the rim. Eventually, they would overshoot the rim and start rubbing on the tire sidewall. This is one of the fastest known ways to destroy a tire.
In recent years U-brakes have been making a bit of a comeback on freestyle bikes.

Adjusting U-brakes:

First, remove the arms from the studs, make sure the studs are free of rust. Coat the studs liberally with grease (this is VERY important!)
Install the arms with them at their maximum spread and tighten the bolts that hold them to the frame. This is how you set the springs. Only connnect the transverse cable after this has been done.

There is usually a small setscrew on the side of one of the arms for fine adjustment of spring balance.

Set the transverse cable as short as possible for best braking. Check the brake shoe adjustment frequently--due to the location of the pivot studs on these brakes, as the brake shoes wear they hit higher and higher up on the rims. If you don't keep on top of the adjustment, they will eventually start rubbing on the tire sidewall. Many thousands of tires have been ruined by this


Last edited by pete_mcc on Tue Apr 24, 2007 10:57 pm, edited 1 time in total.

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 Post subject:
PostPosted: Tue Apr 24, 2007 10:57 pm 
Retro Guru

Joined: Fri Nov 03, 2006 12:28 am
Posts: 1732
Location: italy
Jezz somebody once suggested to run Maguras with the mounting hardware installed upside down. Never tried though...


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 Post subject:
PostPosted: Tue Apr 24, 2007 11:00 pm 
Old School Grand Master
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Joined: Tue Jul 05, 2005 3:14 pm
Posts: 13403
Location: Warwick
Aha - friendly advice thanks guys.

Magura would be cool but Id have to fit fronts too to make it balanced looking. Sorry but I hate odd levers errk..

Good tips Pete but still cant understand why one side pulls more than the other. Seems balanced at cable hanger end. Will hit with hammer untill it is resolved (or until frameset suffers so much I'll have to tip it)

;)


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 Post subject:
PostPosted: Tue Apr 24, 2007 11:01 pm 
Old School Grand Master
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Joined: Tue Jul 05, 2005 3:14 pm
Posts: 13403
Location: Warwick
Wow - Trimbles are hollow!

Polyfiller anyone?


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 Post subject:
PostPosted: Tue Apr 24, 2007 11:23 pm 
South West Deputy AEC
South West Deputy AEC
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Joined: Mon Mar 27, 2006 9:16 pm
Posts: 1840
Location: Wilts
Jez, i think they are for show, as mine don't work either :cry:
It seems that you have to bend the levers to get them to resemble a semi working brake.
So with all this in mind, i don't bother with the little details like even arms :!:
I just use the front brake and use the force :shock:


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 Post subject:
PostPosted: Wed Apr 25, 2007 8:57 am 
King of the DuckBoard
King of the DuckBoard

Joined: Sun Jan 28, 2007 12:30 pm
Posts: 21466
If you did go the Magura route. Then you will have to change the brake boss to canti boss. Then the new magura will fit. Or fit Dia-comp 990 easy to fit and look after. (and lighter)


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 Post subject:
PostPosted: Wed Apr 25, 2007 9:59 am 
Ain't no party like an S Club party
Ain't no party like an S Club party
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Joined: Thu May 25, 2006 4:54 pm
Posts: 7130
Location: UK
Jez,

I've been having similar issues with the u-brake on the gt and have been thinkng of replacing it with a dc 990.

found this site though before and have been meaning to post it - now seems as good a time as any...

http://www.customriders.com/prodlist.as ... d=3&sort=3

does anyone know if any of the other u-brakes listed would work?
possibly a stupid question, but was thinking spacing etc...


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 Post subject:
PostPosted: Wed Apr 25, 2007 11:04 am 
BoTM Winner
BoTM Winner

Joined: Thu Jan 19, 2006 1:23 pm
Posts: 2763
Location: NW England
'Trick' U brakes are big in BMX at the moment, mainly because lightweight and anodised stuff is big at the moment. remind anyone of anything? Anyway like most trick canti's they can be a PITA to set up but I've found the odyssey evolver U brake to be superb, easy tos et up and very solid.


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 Post subject:
PostPosted: Wed Apr 25, 2007 11:25 am 
Ain't no party like an S Club party
Ain't no party like an S Club party
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Joined: Thu May 25, 2006 4:54 pm
Posts: 7130
Location: UK
sorry for the hijack jez...

anyone got any experience of the flybikes stuff?

just wondering whether they're compatable with mtbs or whether bmxs have different stud spacing...?


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