Weinmann Center Pull Brake Problem
 

I'm having an issue with the Weinmann center pull brakes on my '72 Grand Sports. The front brake is fine, but the rear doesn't spring back they way the should. When I pull the brake lever everything seems fine, but the lever doesn't return to it's normal position after being released. It is definitely not an issue with the lever or wiring, it just seems like the brake's spring is not as responsive as it should be so it doesn't pull the wire back into the starting position.

I took it off and scrubbed the springs with some degreaser and that seemed to help for a day or two, but the problem has since returned. Anyone else ever deal with this or have any suggestions to remedy my problem.

Thanks

Did you lubricate the mechanism after degreasing it? Did you clean the pivot points as well as the springs? Are the fasteners torqued properly? Is there a "lip" on a brake pad which is hanging up on the rim? Springs typically do not get tired, I would look at friction somewhere as the probable culprit.

cable may be seized, rusty inside the housing,
replace the cable with a die drawn one and new housing ,teflon plastic lined.

Remove the yoke from the crossover cable, thereby isolating the brake completely from the lever cable. Now try applying the brake by pulling just the crossover cable. If the return is sluggish, then there is a problem is in the brakes (there may still be another one in the brake cable). If the return is crisp, then the problem is between the levers and the brake.

If it's the latter, one often overlooked complication for rear centerpulls is the cable arc leading to the rear hanger. If it's too long or too short, the inner cable will rub against the outer cable. A more obvious complication with rear centerpulls, is that the inner cable must not rub against either the hanger or the outer cable as it leaves the hanger.

OP states that there is "definitely not" a cable problem. This may or may not be true.

There are a number of causes, and the OP needs to divide and conquer. Step one remove the wheel (or shoes) and flex the arms by squeezing from the sides, or lifting the yoke, (not using the lever) and see if the action is smooth and crisp. If not the problem is in the brake, if yes, it's elsewhere.

As I remember, Weinmann brakes allowed adjustment of the pivots (it's been dacades so forgive me if I'm wrong), so it's possible that one pivot is set too tight. Back off the bolt and retighten the locknut on the back. If the play isn't adjustable (like on canti's) then odds are the tube the arms ride on is a bit short and the bolt is compressing them slightly. Here the fix is to thin one arm, or washer slightly so the bolt bottoms on the tube before compressing the arm.

If the brake itself is fine, then possibly the shoe is hanging under the rim by a lip that forms with wear. On my commuter, the first indicator of brake shoe wear is that the brake stays on after I stop, and releases the moment I move. Otherwise look at the cable, which is the most common cause of poor rear braking.

This is true. While I appreciate all feedback, the cable and housing are brand new and I am 100% confident (through diagnosis similar to both SBinNYC's and FBinNY's suggestions) that the problem lies with the brake itself.

If adjusting the pivots entails tightening/loosening the nut & bolt that holds the spring, I will give this a try. I'm not sure what "lubricating the mechanism" entails, but it seems like friction is certainly a viable culprit. I will try something to alleviate this, but if anyone could provide some specifics I would appreciate it.

The bolt and nut don't hold the spring per se. The spring winds around it, but is sandwiched in place and held by the ends, one in the arm, and one in the fixed bridge (back plate or whatever).

The bridge is threaded, (remember it's been 40 years) so loosening the lock nut will allow the bolt to be backed off enough to free the arm, then the nut is tightened to keep it locked in place.

As far as lube goes, Weinmann arms ride on nylon bushings, so only a very light oil (if any) is needed.

The springs are quite strong so are very unlikely to be the issue. In the same vein lubrication is not likely the issue either - it makes things move smoother but that brake will not bind just from lack of lube.

The pivots could very well be the issue, but there indeed is no "adjustment" of them per se. The pivot bolt is firmly tightened onto a bushing that prevents the bolt from pushing on the arm and binding it. The nut in the back is merely there to help lock the bolt in place. If one severely overtorques the pivot nut the inner bushing can be distended, causing the pivot to bind. Now relying on my memory, but I believe I was able to save these sometimes by carefully filing the inner bushing.

Thank you, as I said, it's been a while. In this case the adjustment must be made with a file, thinning the arm (or a washer) so the bolt and nut can tighten on the bushing without binding the arm.

In any case the OP can discover this for himself. If when he removes the nut the bolt is free to fall out, it's not adjustable. If without the nut the bolt is still threaded to the bridge then it is. Either way he can deal with it accordingly. I only offer the threaded bridge possibility because I have vague memories of dealing with brakes where the back nut fell off but the bolt stayed in place.

Well, it appears you responded to my post when I had posted but then realized I needed to edit further. I was relying on my memory also, but I finally found an exploded diagram at

http://www.flickr.com/photos/stronglight/3720926342/

Part number 15 is the liikely culprit. I'm not sure whether the pivot can be readily adjusted, as I remember there being too much slop in the threads unless the bolt was tight against the bushing. The washer/nylon end bushings can't be filed, of course, and filing the arms may not work if the bushing has mushroomed at the ends, therefore binding on the nylon bushings.

Thanks for the diagram, though it doesn't clarify whether the bridge (part 21) is threaded. If it is then it's a simple adjustment.

If not then it depends on the bushing #15 being longer than the arm it goes through, so the bolt bottoms to the bushing's face rather than the arm. I doubt the OP will find a new bushing, so since he can't make the bushing longer, he can make the arm a hair thinner to re- establish the proper relationship between the two.

Unfortunately, part #15 on the diagram is not applicable to my brakes - it doesn't exist. I would consider the fact that it is missing, but it does not exist on my front brake either. I just disassembled the entire brake, cleaned everything as best as possible, and still I'm having issues. Other thoughts?

Either the bridge is threaded, or there needs to be a bushing of some kind so that the bolt can be tightened without compressing the arm. The other possibility is a shoulder bolt which has a set length which the arm rides.

Take another look, or take the brake apart and lay out the parts in line and post a photo. Weinmann made those brakes for 20-30 years (or more) so there may be various versions.

Did you lubricate the areas where part 15 would go if it did exist?

I suspected it might not be quite the same, as there were different Weinmann models. Absolutely we need a pic with the brake fully disassembled. Unfortunately I disposed of much of my store of old bike parts, so have nothing to refer to.

Here you go:
http://i711.photobucket.com/albums/w...d/IMAG0357.jpg

Ok, I guess I didn't FULLY disassemble as I have found the now infamous part #15. I will try to file this down.

NO!!!!! Don't file part 15!!!! The brake is binding because it's too short, not too long.

You want to thin the arm itself a tiny bit so the bushing can extend out both sides at once, and the bolt can't touch the arm itself.

If it's mushroomed you sometimes have to file, but the outside, NOT the end. Now that you have it disassembled you can easily determine if the bushing is the problem. Merely reinstall the arm without the springs and without tightening the bolt. If either arm does not pivot very easily then the bushing has been distended. You can try to fix as I have indicated, but it's difficult to get just right. I believe the bushings were bronze (soft metal) so actually sandpaper is better than a file, and use only until the binding is reduced to an acceptable level. If you go too far you will have play in the arms.

Personally I would just try to find someone with an extra caliper.