U brake questions
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U brake questions
I'm fixing up a 1989 Specialized rockhopper (I think it's an '89, late 80s for sure with the u brake) for my nephew as a commuter/college bike. It's around 10 years older than he is so he thinks it's seriously vintage.
The u brake isn't working right. The left arm (on the non drive side) has weak spring action. The right has a very strong spring action. I took the arm apart and the spring on the left side looks great. Put it back in and no joy.
So I think these are my options:
(1) Buy a new u brake. They're easy to find but they all have pretty short reach since they're designed for bmx bikes (30-50 mm); the u brake on this bike has a reach of 90 mm. Or am I just measuring this wrong? Is there a new u brake that will work on an old mountain bike?
(2) Find a used MTB u brake.
(3) Replace the spring? The spring looks a lot like the spring you would find on a cantilever so maybe I can track down an old canti and just rob the spring.
Any other options? The bike looks pretty good and it's ready to go once I get the u brake working.
The u brake isn't working right. The left arm (on the non drive side) has weak spring action. The right has a very strong spring action. I took the arm apart and the spring on the left side looks great. Put it back in and no joy.
So I think these are my options:
(1) Buy a new u brake. They're easy to find but they all have pretty short reach since they're designed for bmx bikes (30-50 mm); the u brake on this bike has a reach of 90 mm. Or am I just measuring this wrong? Is there a new u brake that will work on an old mountain bike?
(2) Find a used MTB u brake.
(3) Replace the spring? The spring looks a lot like the spring you would find on a cantilever so maybe I can track down an old canti and just rob the spring.
Any other options? The bike looks pretty good and it's ready to go once I get the u brake working.
Last edited by bikemig; 06-28-20 at 08:12 PM.
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On the chainstay U-brake mount, is there more than one hole that the spring can fit into? No?
Is there a bolt on the side of one of the caliper arms? If yes, then turn that bolt in or out to increase/decrease spring tension.
Some of the videos I've watched show a flat on the U-brake spring holder. You turn that flat and hold it in position and then tighten the retaining bolt that holds the brake arm to the brake stud.
Cheers
Is there a bolt on the side of one of the caliper arms? If yes, then turn that bolt in or out to increase/decrease spring tension.
Some of the videos I've watched show a flat on the U-brake spring holder. You turn that flat and hold it in position and then tighten the retaining bolt that holds the brake arm to the brake stud.
Cheers
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On the chainstay U-brake mount, is there more than one hole that the spring can fit into? No?
Is there a bolt on the side of one of the caliper arms? If yes, then turn that bolt in or out to increase/decrease spring tension.
Some of the videos I've watched show a flat on the U-brake spring holder. You turn that flat and hold it in position and then tighten the retaining bolt that holds the brake arm to the brake stud.
Cheers
Is there a bolt on the side of one of the caliper arms? If yes, then turn that bolt in or out to increase/decrease spring tension.
Some of the videos I've watched show a flat on the U-brake spring holder. You turn that flat and hold it in position and then tighten the retaining bolt that holds the brake arm to the brake stud.
Cheers
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I am remembering some versions of the rear Shimano U-brake where one had to remove the pivot bolt and then insert a 6mm hex key to wind the spring, followed by holding it (the arm) in place and then re-installing the bolt.
I also recall that perhaps the correct direction to turn the hollow hex was not so intuitive. I found it maddening at first, and with time having passed I vowed to never mess with these unless absolutely necessary!
The parts are robust so not prone to failure in this area.
I also recall that perhaps the correct direction to turn the hollow hex was not so intuitive. I found it maddening at first, and with time having passed I vowed to never mess with these unless absolutely necessary!
The parts are robust so not prone to failure in this area.
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If you get to the point where you need to replace the brake, Dia Compe still makes their AD-990 brake and it should have pretty similar specs to the Shimano brake. Plus the spring adjustment is super easy with the BMX-style spring tension nuts on each pivot. And at $30 a piece, pretty well-priced.
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Forgive me if I'm stating the obvious, but just to be sure:
Have you read Sheldon's instructions for u-brakes or Park Tools' instructions?
You know how the tension is set, right?
"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."
Have you read Sheldon's instructions for u-brakes or Park Tools' instructions?
You know how the tension is set, right?
"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."
Last edited by John Nolan; 06-29-20 at 04:55 AM.
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I am remembering some versions of the rear Shimano U-brake where one had to remove the pivot bolt and then insert a 6mm hex key to wind the spring, followed by holding it (the arm) in place and then re-installing the bolt.
I also recall that perhaps the correct direction to turn the hollow hex was not so intuitive. I found it maddening at first, and with time having passed I vowed to never mess with these unless absolutely necessary!
The parts are robust so not prone to failure in this area.
I also recall that perhaps the correct direction to turn the hollow hex was not so intuitive. I found it maddening at first, and with time having passed I vowed to never mess with these unless absolutely necessary!
The parts are robust so not prone to failure in this area.
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If you get to the point where you need to replace the brake, Dia Compe still makes their AD-990 brake and it should have pretty similar specs to the Shimano brake. Plus the spring adjustment is super easy with the BMX-style spring tension nuts on each pivot. And at $30 a piece, pretty well-priced.
Do you know the reach on this? Or have you installed this on a MTB with a u brake?
This is the manufacturer's site on the u brake but it does not provide the specs. The u brakes I have found online are, I think, too short to work on this bike.
https://www.diacompe.com.tw/product/ad990/
Last edited by bikemig; 06-29-20 at 09:50 AM.
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Forgive me if I'm stating the obvious, but just to be sure:
Have you read Sheldon's instructions for u-brakes or Park Tools' instructions?
You know how the tension is set, right?
"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."
Have you read Sheldon's instructions for u-brakes or Park Tools' instructions?
You know how the tension is set, right?
"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."
Thank you for this post. The brakes worked perfectly before though (I've had the bike for a few years) and the tension proved insufficient when I fixed the bike up to ship to my nephew. I assumed that this was due to a parts failure which is why I was thinking about a replacement in my initial post. Still I need to try this out and see if it solves the problem!
Last edited by bikemig; 06-29-20 at 09:56 AM.
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Those directions from park and from Sheldonbrown.com may not apply to the OP's U-brake.
There are some huge variations in the sprung pivot design on some Shimano U-brakes that require certain knowledge and/or experimentation/research to assemble properly.
Fear not though, it's doable!
There are some huge variations in the sprung pivot design on some Shimano U-brakes that require certain knowledge and/or experimentation/research to assemble properly.
Fear not though, it's doable!
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I have those brakes, and those instructions seem appropriate.
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I replaced the Shimano U-Brake on my 87 Fisher Hoo-koo-E-Koo with this and it worked well after I replaced the pads. https://www.modernbike.com/diatech-g...-black-u-brake
I can't vouch for your exact situation but your u-brake looks very similar to the one I replaced. I bet a new u-brake would work, but if you go that route, buy from a shop that allows returns just in case.
I can't vouch for your exact situation but your u-brake looks very similar to the one I replaced. I bet a new u-brake would work, but if you go that route, buy from a shop that allows returns just in case.
#13
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I have the same Shimano Deore UBrake on my 1988 GT Karakoram. the instructions noted above worked perfect for me
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I replaced the Shimano U-Brake on my 87 Fisher Hoo-koo-E-Koo with this and it worked well after I replaced the pads. https://www.modernbike.com/diatech-g...-black-u-brake
I can't vouch for your exact situation but your u-brake looks very similar to the one I replaced. I bet a new u-brake would work, but if you go that route, buy from a shop that allows returns just in case.
I can't vouch for your exact situation but your u-brake looks very similar to the one I replaced. I bet a new u-brake would work, but if you go that route, buy from a shop that allows returns just in case.
So I guess with u brakes, you measure from the bolt hole which the arm is screwed into. If that's the case, then the reach on my bike is 44 mm and this brake will work perfectly. I may give this a try since Modern Bike is a few blocks from my house which makes returns easy as pie.
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Yeah I've been wondering how to measure the reach on a u brake. If I measure from the "center" of where the two arms cross, I get a reach of a bit over 90 mm. With caliper brakes you measure from the bolt hole brake center but of course there is no center bolt with a u brake.
So I guess with u brakes, you measure from the bolt hole which the arm is screwed into. If that's the case, then the reach on my bike is 44 mm and this brake will work perfectly. I may give this a try since Modern Bike is a few blocks from my house which makes returns easy as pie.
So I guess with u brakes, you measure from the bolt hole which the arm is screwed into. If that's the case, then the reach on my bike is 44 mm and this brake will work perfectly. I may give this a try since Modern Bike is a few blocks from my house which makes returns easy as pie.
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Cool. That is one possible solution.
Do you know the reach on this? Or have you installed this on a MTB with a u brake?
This is the manufacturer's site on the u brake but it does not provide the specs. The u brakes I have found online are, I think, too short to work on this bike.
AD990 | DIA-COMPE
Do you know the reach on this? Or have you installed this on a MTB with a u brake?
This is the manufacturer's site on the u brake but it does not provide the specs. The u brakes I have found online are, I think, too short to work on this bike.
AD990 | DIA-COMPE
By the way, I see someone else posted a Dia Compe Diatech 996 brake ("Gordo"). Be aware that this model is die-cast instead of forged, which is a weaker production method. The 990 model is forged and only $10 more. Plus I much prefer the adjustability of the post-mount brake pads on the 990 than the threaded mount of the 996.
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I ended up having to replace the rear u brake. I couldn't get the tension right and I didn't want this to fail down the road. I bought a black ops rear u-brake mainly because it was available locally. The price wasn't bad at $20. It is melt forged.
It's as easy as pie to adjust the spring tension on these brakes. I learned a few things. One is that the reach on u-brakes is measured from the frame braze on to the opening on the brake. That makes sense but I wasn't certain of that before buying one. The other is that the brake pad that came on the new u-brake was too long. To work right on an old MTB with the u brake under the chain stays, I needed to replace them with the shorter brake pads and holders found on road bikes. U-brakes are a pain to work on and a stand is a big help.
In my experience, u brakes are a solid design. They did not work well for mountain biking because they got gunked up. But they are fine for road riding which is what this bike is going to be used for. I've been riding the bike around and everything is working well. I'll ride it a few more times over the weekend and then ship it off to my nephew who is looking forward to his new old bike.
It's as easy as pie to adjust the spring tension on these brakes. I learned a few things. One is that the reach on u-brakes is measured from the frame braze on to the opening on the brake. That makes sense but I wasn't certain of that before buying one. The other is that the brake pad that came on the new u-brake was too long. To work right on an old MTB with the u brake under the chain stays, I needed to replace them with the shorter brake pads and holders found on road bikes. U-brakes are a pain to work on and a stand is a big help.
In my experience, u brakes are a solid design. They did not work well for mountain biking because they got gunked up. But they are fine for road riding which is what this bike is going to be used for. I've been riding the bike around and everything is working well. I'll ride it a few more times over the weekend and then ship it off to my nephew who is looking forward to his new old bike.
Last edited by bikemig; 07-10-20 at 10:29 AM.
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Pretty bike! Love yellow and blue.
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Does anyone else with a U-brake in back have a U-brake or SunTour RollerCam (same above-rim pivot mounting) up front? Your Rockhopper has a regular cantilever (pivots below rim) up front, as do the other Project KOM-10s I have seen. Is mine that unusual?
For the record, I am extremely pleased with both brakes on my KOM-10.
For the record, I am extremely pleased with both brakes on my KOM-10.
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Nishiki had Rollercams front and back as well as High Sierra's.
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Most of what you describe about working with the u-brake has nothing to do with it being a u-brake. A u-brake mounted on the seat stays or the fork does not present these problems, including those related to riding in dirt/mud.
I see your new u-brake has flats for adjusting the tension on each arm individually. That design does make balancing the brake a LOT easier.
I have been able to use long-ish brake pads on u-brakes in a couple cases. The end of the pad hits the stay / fork when the brake is released for wheel removal, but it still releases enough to allow the wheel to be removed. A wide tire might need to be deflated first.
John E , my GT Outpost has u-brakes mounted on the seat stays and fork. My Schwinn High Sierra has roller-cam brakes mounted on the seat stays and fork.
I see your new u-brake has flats for adjusting the tension on each arm individually. That design does make balancing the brake a LOT easier.
I have been able to use long-ish brake pads on u-brakes in a couple cases. The end of the pad hits the stay / fork when the brake is released for wheel removal, but it still releases enough to allow the wheel to be removed. A wide tire might need to be deflated first.
John E , my GT Outpost has u-brakes mounted on the seat stays and fork. My Schwinn High Sierra has roller-cam brakes mounted on the seat stays and fork.
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Most of what you describe about working with the u-brake has nothing to do with it being a u-brake. A u-brake mounted on the seat stays or the fork does not present these problems, including those related to riding in dirt/mud.
I see your new u-brake has flats for adjusting the tension on each arm individually. That design does make balancing the brake a LOT easier.
I have been able to use long-ish brake pads on u-brakes in a couple cases. The end of the pad hits the stay / fork when the brake is released for wheel removal, but it still releases enough to allow the wheel to be removed. A wide tire might need to be deflated first.
John E , my GT Outpost has u-brakes mounted on the seat stays and fork. My Schwinn High Sierra has roller-cam brakes mounted on the seat stays and fork.
I see your new u-brake has flats for adjusting the tension on each arm individually. That design does make balancing the brake a LOT easier.
I have been able to use long-ish brake pads on u-brakes in a couple cases. The end of the pad hits the stay / fork when the brake is released for wheel removal, but it still releases enough to allow the wheel to be removed. A wide tire might need to be deflated first.
John E , my GT Outpost has u-brakes mounted on the seat stays and fork. My Schwinn High Sierra has roller-cam brakes mounted on the seat stays and fork.
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bikemig
One nice thing about under the chainstay mounted brakes (not that you seem to need it) is that there's nothing to snag on a pannier that's mounted far forward. Especially the old straight arm cantilever brake arms that stuck straight out were prone to getting snagged on a pannier and holding the brake pad(s) against the rim. Not nice if it happened going up a hill.
I had an old Bianchi MTB that had lots of clearance between the rear of the seat tube and the tire even with fenders on. I used to carry an extra water bottle there. It was a 750ml (20 oz) one complete with cage.
I think U-brakes or roller-cam brakes under the chainstays are great for a touring bike.
Cheers
One nice thing about under the chainstay mounted brakes (not that you seem to need it) is that there's nothing to snag on a pannier that's mounted far forward. Especially the old straight arm cantilever brake arms that stuck straight out were prone to getting snagged on a pannier and holding the brake pad(s) against the rim. Not nice if it happened going up a hill.
I had an old Bianchi MTB that had lots of clearance between the rear of the seat tube and the tire even with fenders on. I used to carry an extra water bottle there. It was a 750ml (20 oz) one complete with cage.
I think U-brakes or roller-cam brakes under the chainstays are great for a touring bike.
Cheers