Repairing A Limp Caliper Brake Arm
 

I know there are probably thousands of articles and YouTube vids about this, but can someone tell me if there is an ultimate guide to getting both sides of a 1990's-vintage caliper brake to spring back after being applied? On an old mountain bike I am trying to restore, the plastic sleeve that covers the tension spring and creates space between the frame and the brake arm on one side is cracked and missing. I replaced it with the exact part from another bike and I still can't get the non-drive side of the brake caliper to release from the rim after I apply the brake. I know I have fixed some of these over the years, but I don't remember how or if, in fact, I just got lucky. Help?

With so many variations on calipers... Can you post a pic and I might be able to help more

I was afraid someone would say that. OK, give me a day or so, as I no longer have an iPhone and my flip phone camera is a pain-in-the-butt to transfer photos from.

Meanwhile, isn't there a universal trick to accomplish this?

without knowing what "calliper brake" you are asking about, pretty much impossible

I suspect they're canti lever brakes

The better designed canti brakes have at least one side's spring being adjustable. Many bike canti boss mounts have 3 spring mounting holes. Some cantis have two spring end holes in the pivot to further adjust the spring rate WRT the second side. But there's a lot of cheapo bikes/cantis with no spring adjuster, bikes (and sprung forks) with only one hole in the boss for the spring end and there's the usual wear/grit/corrosion issues that plague any rim brake with separate pivots for each arm.

Having said all that it's pretty well known in our industry that a broken/missing spring cover (the plastic part) can and usually will cause that side's arm to not release like it did when the spring cover was intact.

Looking forward to seeing what's really going on here. Andy

Sounds like Vs and he described the dust boot. With both double check the fixing bolt isn't too tight, undo the cable and wiggle it to see if its smooth or not, if tight, back off the fixing bolt and see if that helps, if it fixes it don't tighten it back down hard. if it still feels tight spray some lube in. Still tight pull the brake off and emory cloth the boss it bolts onto, grease it and reinstall. If it wasn't tight and wiggled freely to begin with check the plastic cover around the spring, Some shimano cantis were especially prone to this breaking and losing all spring tension as a result. If it dosnt have this make sure it isn't just the pad worn and sticking to the rim which is fixed bt adjusting pad location. If these don't cover it then pics.

Here are pics of both the front and rear canti's. The front still has the spring cap, but doesn't spring back after breaking. The rear has no spring cap anymore (I COMPLETELY shattered it while taking the photo!) and also does not spring back.

https://cimg5.ibsrv.net/gimg/bikefor...ffd58d1b78.jpg
https://cimg6.ibsrv.net/gimg/bikefor...5b2d23f5ce.jpg

In your last picture, it looks like the spring is in the uppermost hole on the frame tab (if there are multiple holes), which would provide the most spring pressure. If this is the side that doesn't return, then I would suspect a broken spring (or one that's really loosened up over the years). The usual advice applies here regarding ensuring correct lubrication of the brake arms and studs. Does the sticky side swing freely and without resistance by hand when not connected to the cable or yoke? If so, then it's probably not a lubrication problem and is more likely a problem with the spring and/or how it's seated in the brake arm. If it doesn't swing freely, then there's probably something going on with the stud (perhaps it's mushroomed or swelled, or there's a lot of gummy grease somewhere, etc.).

If nothing appears broken with the spring, but it's just not working, then the cheapest fix may simply be a new set of brakes. The Shimano BR-CT91s are cheap and available everywhere. For just a few dollars more, the Tektro CR-510s are much better brakes in my experience. Advantages (in my humble opinion) over the CT91 is the use of threaded brake pads (making for much easier setup) and spring tension adjusters on BOTH brake arms, vs. on only ONE arm with the CT91.

Thanks, HokieFyd. Good advice. Until about a month ago, I had a 75-year-old family bike shop in my neighborhood where I probably could have picked up a brand new set of calipers for $5 or nothing at all. Now I am lost. I suppose I will look into the ones you suggested online. The bike is in very good condition and I will probably give it away, so I want it to be safe.

Those old Shimano cantilever brakes worked good untilt he plastic thing cracked, which it almost always did.

Just about any new cantilever brakes will be a good fix, and will come with new brake pads!
Some examples:

https://www.amazon.com/Tektro-Oryx-F...3FSBJJ6PFMT3RM

https://www.amazon.com/Shimano-BR-CT...=fsclp_pl_dp_7

https://www.amazon.com/Tektro-CR720-...=fsclp_pl_dp_6

Those plastic parts had close to a 100% failure rate. Shimano sold them to shops by the bag as replacements.
Unless you have an emotional attachment to those brakes, just replace them.

Nope. Definitely no attachment. I found this Trek MTB in a neighbor's trash two weeks ago. Everything else about it is in great condition. The tires look like they have about 50 miles on them, the wheels are true, gears worked fine after a minor adjustment, and there's not even a significant chip in the paint.

Now that I think about it, I might even have a set of calipers I can transfer from another bike. One way or another, I'm going to save myself a lot of time and greasy hands and just replace both front and rear.

Yep. IIRC, some of the old canti's even had a recall or two 'cause the spring wouldn't release to pull the pad away from the rim.

Don't waste your time with plastic brake parts. Cheap canti's are $15 a set, new. Heck, decent pads can cost almost as little.

I personally would just replace them. probably comes with new link wire and pads too.

https://www.jensonusa.com/Shimano-Altus-CT91-Brakes

I too suspect that's an early Shimano cantilever brake with a cracked, broken or missing return spring retainer cup. There was a recall of those in the mid 90's for that very problem.

My solution is to replace it with a low level SHIMANO V-brake. Much easier to set up, not too pricy and much better functioning than the cheaper brands. To do it right you need longer pull brake levers too.

Just ordered front and rear CT91's for $9.99 each! Thanks for your input, everybody.

When I mount new CT91s I dribble/spray Triflow into the open/back side of the canti, where the spring sits. Then I grease the post/boss and also the mounting bolt's threads. Andy

Gotcha. Thanks!

By the way, the Shimano BR-CT91 calipers were a great call. They went on easily and work great. I think I will order an extra set or two for future fixer-uppers!

Looks like the current CT91 uses the same design, where the plastic sleeve actually holds the spring tension. Granted, the sleeve on the new one isn't 25-ish years old, but, uh, one day it will be.

The plastic looks a little more robust than the original, but yeah, it's still junk. I won't be around to worry about it in 25 years, though.