bikemig 

I'm getting ready to rebuild a new to me 1971 Witcomb that I picked up with a campagnolo nuovo record group. The brakes are long reach, nutted, and the rear has a drop bolt. There is generous clearance on this bike.

The cam is bad on the front but OK (not great) on the rear. From what I can tell based on the schematics, the cams are interchangeable, right? I've never pulled one apart so just asking. Of all the parts in the quick release mechanism, I take it that the cam is the one most likely to go bad, right? You can sometimes find the cams and I'm thinking of just buying a set. Looks like part 2005 is the cam.

Here is a schematic that I found plus a pic of the cams:

Narhay

What do you mean by bad? Badly rusted? They don't move very much in practice so probably not overly worn. Im sure you've tried but they come out with the bolt and nut and could be cleaned up to fit and move better.

repechage

when you cite “bad”, what do you mean?

That eccentric was essentially unchanged for the duration, aside from manufacturing tolerances.

bikemig 

It doesn't hold the quick release lever under tension. In fact there is no tension so the quick release just flops and doesn't open the brakes. I tried tightening the nut down but that didn't do any good.

bikemig 

I have some short reach campys with a good quick release mechanism. I could rob the parts but I hate doing that.

Mad Honk 

bikemig,
When I do an overhaul on a bike the calipers are taken completely apart and then cleaned and reassembled with a light grease on all of the moving parts. During disassembly I drop all of the parts in a solvent bath and then clean each part separately. If rust is present a bit of cleaning with a wire Dremel brush made of brass or low speed with steel brush. A wire brush bit for the drill is what I use to clean the surface of the caliper arm on the interior side of the cam section. Fresh light grease on all moving surfaces and a final testing of the brake caliper for easy movement and correct action. For the smaller diameter section of the cam bolt for the quick release the cleaning is with a small nylon brush in the drill and a bit of Quick Glow chrome cleaner to clean the inner bore of the cam lever. It takes about two hours to completely clean the caliper by disassembly, but that includes stopping for a beer break, or two. Smiles, MH

bikemig 

Mad Honk, that's good advice especially about the beer. The brakes are very clean as was the bike. This is how the brakes came on the bike with no clean up on my part.

Still that's no reason not to take it apart and see what the heck is going on. Given how clean they are though I suspect the cam is bad. I was curious whether this was a failure point.

Drillium Dude 

The cam/QR lever interface is a press/interference fit. Once you undo the tiny nut at the front, the whole assembly will slip out and you'll know what piece is worn. Could be the cam or the QR lever hole itself has somehow been rounded out. Take some pics and let us get a look-see

I have spare parts here. Once you know what you need, drop me a line via PM and we'll get you sorted.

DD

dddd

Sounds like the flats may be rounded in the lever piece(?).

repechage

Reads to me the eccentric is small and the arm bore is big.
I have dealt with this once- test assemble the lever and the cam without the clamp bolt assembly.
your goal is to move the eccentric bore center inboard so it is inboard of the outer eccentric diameter.
on the backside of the arm will show a part of a counterbore facing- mark the lever and the eccentric and review removing enough material of the arm so that the lever rotates more and gets the alignment of the assembly over center, that way the control cable pulls the works tighter not looser.

not mentioned are the brake blocks and holders used- if a substitute set is being used that will be an easy answer - possibly too thick- the same solution might work.
in that case provisionally assemble the caliper without the return spring to evaluate.

oneclick 

That cam is (supposed to be) an over-centre action. It does (should) not need to be tight to work - once it goes over centre cable tension (should) hold(s) it there.

If it won't hold it may not be going over-centre. Check that something isn't stopping it from completely rotating. and that it is assembled correctly.

Mad Honk 

bikemig,
From the pictures posted everything looks correct. Perhaps there is something going on on the other side of the brake caliper. I would also wonder whether the cable clamp was holding the cable in the slot designed for it. If the cable was clamped on the outside of the holding washer it could produce the issue you are having. Smiles, MH

bikemig 

I pulled the brake apart this morning. The parts look OK and they were put together correctly as far as I could tell. There's not a lot of choice here in terms of how the parts go together and they fit the schematic.

The problem is that the quick release is loosey goosey (I think that's the right technical term) thoughout the movement. So the brakes don't open with the quick release. With all my other quality sidepulls (including campy) there is tension thoughout the range of motion and the brake opens and closes as you move the quick release. WIth these nothing. That's why I was thinking a bad cam as that is the most likely I think to go bad. Still it's weird that both went bad? Maybe there is a trick to putting this together?

Road Fan

I think Mad Honk's advice is great, but incomplete. What kind of beer????!!!!!!

Road Fan

Possibly this is a silly problem, but when one is tired, silly mistakes can be made, resulting in silly problems.

Perhaps you did not install the cable correctly. The working tension of the brake cable is intended to actuate the brakes when the lever is down.

Another is the direction of the cable when lever is down. This is an over-center mechanism, where the lever stays down because the line of the cable when lever is down in inboard (closer to the center plane of the bicycle), and the little extra force that results is what holds the Q/R in its not-opened position. The cable needs to be under tension when the lever is down and the brake is not actuated (lever not pulled, but cable is in place all attached) in order for this to work.

Things that are simple and not elegant are usually easy to see. Things that are simple and elegant are sometimes tricky to see, leading to silly problems. This over-center QR design is IMHO a great example of elegant mechanical design.

We could create much more dangerous silly problems, believe me!

Kabuki12

I have come across some pretty crusty NR brake sets that I have completely disassembled and rebuilt. I haven’t come across one yet that didn’t work smoothly after rebuild. They are only designed to move about 130 degrees within their quadrant so I think it would be rare that one would be worn that much unless the brake has been damaged. The cam works by the angle of the cable in relation to the fixing or retention assembly. That’s what keeps it from releasing. The center of rotation of the cam in relation to the adjuster guide is what I’m referring to. You may check the pivot bolt to see that it is not too tight.No beer here , just the facts!

bikemig 

This is a likely solution. I didn't install these brakes. They came on a 1971 Witcomb that I just took apart so I could work on the frame. They may well have been incorrectly installed. I have a hard time believing that both cams are bad. These are tough brakes.

Road Fan

I have trouble believing that one cam is bad!

bikemig 

Agreed. But on my other high end brakes (superbe for example) the cam works to hold the tension even when the brake is not installed and there is no cable. With campy, the tension only works if it is correctly installed?

repechage

Move to Supurbe brakes then

bikemig 

Nah if I were going to move to anything it would be a set of weinmann 610 centerpulls, which would look right on an old Brtish bike like this.

repechage

A British bike, just go full Nationale, John Bull calipers, for the All Steel bicycle.

Mad Honk 

bikemig,
I suspect the problem might have been an incorrect cable tension on the installed caliper. I just picked out a caliper that had been re-furbished. I use a straight pull spoke to hold the pieces in place while they are in the parts bin. I closed the caliper enough to put tension in the springs and re-clamped the cable screw. There is pressure through out the movement from closed to open as a result of the spring tension. Try re-assembling you caliper and use either a short piece of cable or a spoke to add tension to the spring. The movement on mine changes from closed (1-1/8") to open (1-5/16") so the movement is not very much laterally. But with the spring tension applied the brake works normally. If the original build did not have the cable tension correct, the cam would be loose in operation. Even when set to the open cam position, the brake will function but without the force that is applied when in the closed position. Add some tension and see if it works better. Smiles, MH

Road Fan

No, sorry! If the brake is not installed but is correctly sssembled, and you squeeze the brake shoes together, you need to feel considerable resistance and springback when you squeeze the brake shoes. That means the springs are installed correctly and are the same on each side. Obviously the same thing must happen once the brake is bolted onto the frame or fork. It should also remain that way after the cable is installed.

Road Fan

Yes, exactly!