Go Back  Bike Forums > Bike Forums > Bicycle Mechanics
Reload this Page >

Tektro CR720 brake arm sticking, and it's not the spring

Notices
Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

Tektro CR720 brake arm sticking, and it's not the spring

Old 12-20-15, 06:39 PM
  #1  
Senior Member
Thread Starter
 
Join Date: Aug 2007
Location: Chicago
Posts: 114

Bikes: Surly Cross-Check; Bianchi San Jose; Schwinn Super Sport.

Likes: 0
Liked 0 Times in 0 Posts
Tektro CR720 brake arm sticking, and it's not the spring

I was upgrading my Surly crosscheck from Tektro Oryx cantis to CR720s. As I was dialing in the new brakes, I noticed the left brake on the front is not springing back. It's catching after the pad makes contact with the rim. It seems to not be the spring, as even with the spring removed, the brake arm still catches and will not freely move back into position. I've cleaned the post, and tried the brake arm with and without grease, and the brake catches on the post no matter what. It's almost as if the brake arm is snagging on something, but can't imagine what. Any ideas what's wrong?
rohmen is offline  
Old 12-20-15, 07:20 PM
  #2  
Senior Member
 
Andrew R Stewart's Avatar
 
Join Date: Feb 2012
Location: Rochester, NY
Posts: 18,183

Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Mongoose Tomac ATB, GT Bravado ATB, JCP Folder, Stewart 650B ATB

Liked 3,992 Times in 2,373 Posts
So without a wheel in place the arm freely rotates beyond the range needed in use? And when a wheel is in place the arm won't spring back after the pad makes contact with the rim? Fist thing I'd look at is whether the pad has a lip along it's bottom edge. With cantis as the pads wear they tend to contact the rim lower and lower down the rim's height. In time the upper portions of the pad wear more and the lowest part doesn't, resulting in a lip. This lip can catch on the rim's edge and hang up. Sometimes only when the rim is stationary but not when moving. Many current cantis only have spring tension at the very end of the arm's travel in toward the rim. (The whole "Light Action" thing I find issue with. But I never suffered from weak hands...) This lack of high return spring tension only compounds and pad catching. Andy.
Andrew R Stewart is offline  
Old 12-20-15, 07:46 PM
  #3  
Senior Member
 
dsbrantjr's Avatar
 
Join Date: Sep 2010
Location: Roswell, GA
Posts: 8,321

Bikes: '93 Trek 750, '92 Schwinn Crisscross, '93 Mongoose Alta

Liked 1,095 Times in 725 Posts
I have had issues with two different CR-720 installations. On one, the bushing on the arm was slightly longer than the boss, which caused the arm to not rotate freely when the mounting bolt was tightened. The solution was to file the bushing slightly shorter, perhaps 10 to 15 mils only.
On the second one the boss's diameter was somewhat expanded/mushroomed at the end, likely caused by overtightening the mounting bolt, which again caused binding; this was remedied by filing a slight fillet at the end of the boss it reduce its diameter and allow free rotation. Both were likely due to tight tolerances on the manufacture of the brake arm vs the boss; not necessarily a bad thing and easily remedied in my cases. They both now work splendidly with zero play between arm and boss.
dsbrantjr is offline  
Old 12-20-15, 10:29 PM
  #4  
Senior Member
Thread Starter
 
Join Date: Aug 2007
Location: Chicago
Posts: 114

Bikes: Surly Cross-Check; Bianchi San Jose; Schwinn Super Sport.

Likes: 0
Liked 0 Times in 0 Posts
Originally Posted by dsbrantjr
On the second one the boss's diameter was somewhat expanded/mushroomed at the end, likely caused by overtightening the mounting bolt, which again caused binding; this was remedied by filing a slight fillet at the end of the boss it reduce its diameter and allow free rotation. Both were likely due to tight tolerances on the manufacture of the brake arm vs the boss; not necessarily a bad thing and easily remedied in my cases. They both now work splendidly with zero play between arm and boss.
Thanks. I have a feeling this is what's going on.
rohmen is offline  
Old 12-21-15, 05:58 AM
  #5  
Senior Member
 
dsbrantjr's Avatar
 
Join Date: Sep 2010
Location: Roswell, GA
Posts: 8,321

Bikes: '93 Trek 750, '92 Schwinn Crisscross, '93 Mongoose Alta

Liked 1,095 Times in 725 Posts
The bosses/studs can be replaced if needed; Paragon Machine Works, Problem Solvers and many others have them. Be aware that they come in different threadings, there are at least three different 10mm thread pitches (1.0, 1.25 and 1.5mm) plus 8mm and 6mm used. These guys https://shop.brake-stuff.de/en/18-br...es-canti-studs have the largest assortment I have found.
dsbrantjr is offline  
Old 12-21-15, 10:54 AM
  #6  
Banned
 
Join Date: Jun 2010
Location: NW,Oregon Coast
Posts: 43,598

Bikes: 8

Liked 1,360 Times in 866 Posts
Ones Brazed onto a steel frame can be replaced, by Brazing, but then you have to replace the Burned off paint.
fietsbob is offline  
Old 12-21-15, 12:31 PM
  #7  
Senior Member
 
Join Date: Jun 2013
Location: Bozeman
Posts: 4,094

Bikes: 199? Landshark Roadshark, 198? Mondonico Diamond, 1987 Panasonic DX-5000, 1987 Bianchi Limited, Univega... Chrome..., 1989 Schwinn Woodlands, Motobecane USA Record, Raleigh Tokul 2

Likes: 0
Liked 0 Times in 0 Posts
Are the bearings on the wheel loose? I've seen some... lesser quality bikes have this problem. (I'm not saying your Surly is lesser quality, I have a Cross Check myself!) Sometimes with the loose wheel bearing the pad that contacts first will push the rim over a mm or so then get caught because the brake pad is somewhat sticky and has a good bit of friction on the rim.

Just another view.

Good luck! (Did you try changing pads?)
corrado33 is offline  
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
Chesterton
Bicycle Mechanics
6
07-17-19 04:30 PM
MAK
Bicycle Mechanics
6
12-16-17 01:07 PM
Altair 4
Bicycle Mechanics
19
11-08-16 09:43 AM
efiste2
Bicycle Mechanics
12
05-27-15 05:23 AM
americanlt2
Bicycle Mechanics
1
06-06-14 02:49 PM

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Your Privacy Choices -

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.