Which Cantilever brakes to purchase?

[Brucey]

I'm sure that experience will vary because of the difference in friction coefficient, pad stiffness, bushing wear, and frame stiffness.

I just find that with BR-AT50 brakes the front pads -even when set square or slightly toed in to start with- come out worn 'leading edge first'. I have noted that with very cheap Vs that have the post mount 'hung out to dry' at the front this effect seems very much worse.

I'm sure there is more to squealing etc than this alone, but I am sure that the brake geometry is a significant factor at least.

My thought is that the play in the brake bushing -which should be 'one tube loose over anothe'r more or less- is taken up in one of two ways when the brake is on. It may -if the force vector is well away- be set to twist the bushings right from the start. However if the resultant force vector passes through the bushing itself (pref towards the rear of the bushing w.r.t. the direction of travel), the clearance will be taken up by 'pushing to one side', rather than twisting.

I would say that the 'twisting' mode makes for faster bushing wear, and uneven pad wear, -or at least an unusual toe in requirement.

I believe that some (probably not all) squealing may be due to the force vector passing near the front or rear of the bushing, in which case the brake can tip between 'pushing sideways' and 'twisting' in the bushings.

I've experimented with moving the post mount to the other side as well, but often the parts don't or won't fit, plus it is normally a very big adjustment, and a change of pad type is often required. A 1/4" movement of the force vector is quite large, and moving the post mount gives a lot more than that.

I've also experimented with a few turns of PTFE tape over the boss, to eliminate play, at least temporarily. This does seem to reduce squeal but it may do so because the motion is damped a little. In any event it is not a solution that can be expected to last very long.

I hope my thoughts and experiments are of some interest, anyway

cheers

[PW]

I always plaster the canti studs and bushings with the thickest grease I've got. I seems to work, the present cantis on the tourer are ex- Claud Butler tandem and over 25 years old, still as good as ever.

[CREPELLO]

I've also experimented with a few turns of PTFE tape over the boss, to eliminate play, at least temporarily. This does seem to reduce squeal but it may do so because the motion is damped a little. In any event it is not a solution that can be expected to last very long.

cheers

I tried the same thing using copper grease on the assumption that if it could reduce squeal put on the back of disc brake pads, perhaps it would work it's magic with canti's. It didn't. But it did help to reduce bush wear on some Avid Shortys. For some reason Avid don't grease the bushes at all - they are brass and therefore bound to wear more quickly than steel. Which only increases slop and subsequently, squeal. Which makes me think that if makers of canti's would only fit closer tolerance bearings, squeal would be drastically reduced.

[CREPELLO]

I always plaster the canti studs and bushings with the thickest grease I've got. I seems to work, the present cantis on the tourer are ex- Claud Butler tandem and over 25 years old, still as good as ever.

It's what I like to do as well. But some callipers have there own bush and sleeve which needs greasing. The Avid Shorty it's possible to pop the front washer cap off, dismantle and grease the insides. The modern Shimano canti's seem to be riveted or something, which concerns me that I can't service and grease.

[PW]

Mine are the old long arm Dia Compes with an exposed brass bush direct onto the stud. If you ever see any at a boot sale snatch the seller's hand off.

[pete75]

Presumaby these are now the dog's gollox where cantis are concerned. A bit pricey though.
http://www.chainreactioncycles.com/Mode ... tedKingdom

[Brucey]

Presumaby these are now the dog's gollox where cantis are concerned. A bit pricey though.

-cough cough just a bit.....

but you can save ten quid and get the 2012 model in black....

they seem to be getting with it, design wise- a centrally mounted bolt type pad means that adjustment is easy and the brake will work equally well front and rear. An asymmetic pad would finish it off nicely, but they look symmetric to me. Probably the short pad is the same fit as the road campy ones, and the asymmetric pad is only really worthwhile with a longer pad.

cheers

[531colin]

.............I just find that with BR-AT50 brakes the front pads ...............

I knew it didn't make sense.......since Pete posted..........

With drop bar levers these are probably your best choice. High quality and work well.

http://www.defietsenmaker.nl/index.php? ... 53&lang=EN

I've been talking about those MT 60's.

I shall come back to this after I've been out on the bike......

[Brucey]

apologies for any confusion caused; -the brakes in question although not identical are very similar indeed. The stock blocks are different of course, and post mounting may be very slightly closer to the bushing centre on the MT60s. Although actually the model number is different, functionally they are equivalent in terms of both construction and design.

For a symmetric pad, the stock MT60 ones are pretty good; the chamfered top edge keeps the block on the rim for longer without adjustment as the pad wears.

Given a free hand I would choose a symmetric (or just weakly asymmetric) pad at the rear and a very asymmetric pad at the front with these brakes for the reasons described.

BTW it occurs to me that because the friction coefficient varies a lot in the wet, so does the thrust vector position through the brake; this may help to explain why brake squeal can come and go with the weather.

cheers

[531colin]

Apparently my brakes are BRM732



but they look like the BRMT60 that Pete posted.



Looks like I toed them in when I fitted them....and now the front (trailing) end of the pads have worn down.

[tooley92]

Apparently my brakes are BRM732



but they look like the BRMT60 that Pete posted.



Looks like I toed them in when I fitted them....and now the front (trailing) end of the pads have worn down.

I haven't worked out the difference yet either Colin! and I have a set of each.

BRMT60 - are Deore II and BRMT732 are Deore XT (the last ones before they went lo-profile)

[Brucey]

they did at least half a dozen different models which used slighty different arms, but the same post mountings, same geometry where the post mounts, same bushing construction, were/were not anodized. They all look slightly different and they all work pretty much the same. If I'm not the only one who doesn't know the model numbers by heart then I'm not altogether surprised. The only ones that are a source of concern are those fitted with the aluminium wedge washer. Said washer was fitted on some XT models and is not resistant to British winter. All the others have steel wedge washers.

This is the most toe heavy wear I have seen on front brakes of this kind! It does contrast to my experience for sure. An asymmetric pad is a moot point in this case; there isn't really much room for one, and a long symmetric pad may be the best choice. I don't think a longer pad could be fitted on this frame either.

Q. are those anodized rims?

Nice pics BTW

cheers

[gaz]

.

[531colin]

Can't take much credit for the photos, the camera does the clever stuff, all I do is point it and try not to get too much junk in the background.
I meant to say last night I was a bit surprised how much slop there is in the bushings, the brake waggles a few millimetres.....doesn't seem to matter?
I had a bit of a Google at all the different part numbers of brakes, and they don't look very different to me, so I can't imagine why "Brucey's" experience with the things is so different to mine, which is a shame, I thought we might have been getting somewhere!
BR AT 50 here http://www.velobase.com/velobase.com/ViewComponent.aspx?ID=2b99f8d4-1d96-4f69-bd3f-45b38dd7b7b9 look like they came with a different pad, but they won't last for ever.
Rims are Rigida Snyper, I guess they are silver anodised, but then the brake track is machined afterwards. In any case they have done a couple of winters, so they are now re-surfaced by the pads.

[Brucey]

actually I've had another think about the bushing play issue; looking at the forces in the plane of the frame, the braking force exerts a major twist into the bushing as well. Thus my previous thought was a 'bit too two-dimensional' ; the bushings are probably 'twisted' all the time the the brake is on, in one direction or another. Of course allowing for this is exactly what I do very time I adjust the brakes..d'oh... I guess they still might rattle about during squealing but not in a simple way I expect. Ho hum.

I also had another look at my collection of worn brake blocks. I'm now thinking that at least some of the issues have been with the OE BR-AT50 shoes which are maybe simply not strong enough; I reckon the holder can distort near where the post attaches. Other issues have been with rather short pads, which were unfortunately fitted to a frame with a rather wide boss spacing; an especially bad combination. The best results I have had are with long asymmetric pads (esp front) and just plain long pads (esp rear), on frames where the bosses are close together. Pretty much the same holds true with 'V' brakes too.

cheers