prairiepedaler

I've an old Raleigh Elkhorn which has non-removable Canti bosses front and back. The arms when mounted, front and back, seem to exhibit a little more play than they should. That is, the outside diameter of the bosses are smaller than the inside diameter of the arms by a margin that seems greater than acceptable. I've dropped on identical arms that I had as spares and there appears to be the same amount of play to confirm.

This extra play makes it more difficult to set up your brake pads to the rim because you have to adjust them for a "dynamic" finishing position on the rim ahead of time (i.e. when the pads grab the rim, they "rock" from front to back in the direction of wheel direction) otherwise the back end of the pad will wear first.

Sooo, anyone ever had this problem before? I was thinking about obtaining some 0.001" brass shim stock to take up the slack.

dsbrantjr

A shim would probably work and brass is a good choice, but I think that some careful measurements of the boss and brake would be in order, to avoid a cut-and-try scenario.

dabac

An easier fix is to find a set of cantis that turn on bushings inset into the brake arms instead of against the brake bosses.
This should also be the majority of them.
The screw clamps the bushing to the boss, and no more play at that interface.

fietsbob

Paul comp resolves that by having a separate stainless steel sleeve over the common frame post..

https://paulcomp.com/product-categor...onents/brakes/


+[Magura hydraulic MTB rim brakes, use the posts as a mounting point, but not as a pivot]






....

Andrew R Stewart 

I've used thin brass shim stock, carefully cut and placed over the frame post, to reduce arm slop. It can make a big difference in felt play and can help with some squealing. I strongly suggest having several thicknesses on hand as only a couple thousandths is the difference between too tight and still loose. I think the shims I made have been from .003-.008".


If you do this kind of stuff (deal with thousandths of an inch) having a shim assortment pack like this https://www.mcmaster.com/#9300k29/=1bvqm1b is a nice resource. Andy

prairiepedaler

Hi Ya'll, thanks for the input. Bob, those Paul Comps are nice but Lordy, the price, it burns I tell ya.

So Andy, you had some success in a similar situation so that's encouraging news. I presume your bike didn't have thread-on replaceable bosses.

I'm sourcing a few snippets of 1/1000 from a machine shop. Machinists supply houses have minimum purchases and I'll never use the remaining stuff up, including the pack mentioned from Mcmaster-Carr. Up here you need an account with them now believe it or not.

Dabac, the arms I'm using are the standard old Dia-Compe cantis. These look like they have a bushing in them. It's not the same matieral as the arm alloy anyway. I tried two different identical arms on the posts and the slop is the same.

DSB, this exercise will require some fiddling around with to be sure. I'm hoping the boss wear is uniform, but I doubt it. So, the wear pattern will probably leave an "ovoid" shape to it, not perfectly round. One could go nuts on this frame; sandblast/powdercoat it, drill and braze on new mounts for an extra bottle cage & mid fork blade pannier rack mount and of course replace with replaceable thread-on type canti-bosses. BUT, in the end it's just a heavy old Raleigh after the improvements... and emptier wallet.

I'll try and mess with shims and if that doesn't work I'll probably just leave them be and run the bike as-as.

andrewclaus

Keep in mind, beer cans are about 0.1 mm, or 0.004 in.

prairiepedaler

Ok, finally got some shimstock in 1,2 and 3 thou. Will see how it goes here and post results.

clasher

If the shims doesn't work, I've had some luck cutting off old canti posts (they were bent) and drilling/tapping a hole for the thread-on type bosses. Our local co-op has a drawer of thread-on bosses from old aluminum frames, they also had the tap set I used but it was a standard metric tap from a hardware store tap set. I think buying all that stuff new would still be cheaper than a set of Paul's brakes

prairiepedaler

Hmmm, the chop and tap option might be an angle if neccessary. Careful consideration would be required to ensure the strength, alignment, durability etc are adequate. I'm trying the brass foil this week as a start.

eeuuugh

I've improved sloppy cantis by putting .5mm chainring bolt spacers at the base of the canti boss, which sandwiches the brake arm a little tighter between the base of the boss and the fixing bolt.

prairiepedaler

Hi, didn't that position the arm out past parallel to the end of the boss so that the fastening bolt came in contact with the arm and cause chaffing between the bolt head and arm?

eeuuugh

If the arm is chafing on the bolt head there will be noticeable friction in the brake return, which would mean the shim is too thick. A 1mm spacer will usually make even a sloppy brake chafe like that, and I've run into a couple brakes with annoying play where .5mm also made them chafe, and used an even thinner shim. Also--I should have said axle spacers, not chainring bolt spacers!

fixedweasel

A round or two of electrical tape will do wonders for you.*


*adjust as need

prairiepedaler

Ok, a brief update on the shims. A curl of 2/1000th was used on each caliper mount. Seems to do the job. The calipers don't rotate as freely as I would like but under spring tension they should retract well enough. The improvement in reducing rocking play is satisfactory. For these mounts and calipers (dia-compe) the shim stock dimensions were cut to 26.4mm length / 16.0mm width. I'd recommend mitering the 4 corners of each piece so it they don't catch on anything while mounting.

Update*** Tested the brakes out, working perfectly. Nice and firm, good retraction. Using a brake booster on the front set for extra stiffness. Kool-Stop pads. Should stop this pack mule to-be quite well.