Bicycle Mechanics - Did I buy the wrong cantilever brakes?
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12-22-08, 09:11 AM
I bought these shimano BR-R550 cantilever brakes (http://www.cyclecomponents.com/2/sv/artiklar/racer_cross/komponenter-3/bromsar-2/cross-4/shimano-br-r550-cantilever-broms.html) for this bike (http://cretin.net/~kellen/BRAKES/DSCN0812.JPG) (picture including old brakes (http://cretin.net/~kellen/BRAKES/DSCN0787.JPG)).
BUT!!!! The new brakes don't seem to have enough space to properly close; the pads hit the tire (rear brakes: photo front (http://cretin.net/~kellen/BRAKES/DSCN4678.JPG), photo back (http://cretin.net/~kellen/BRAKES/DSCN4679.JPG)) and the link wire is distorted too much (rear link wire photo (http://cretin.net/~kellen/BRAKES/DSCN4681.JPG)). Additionally, the fork doesn't have much space for v-style brakes, and the pads jam into the fork.
So, the answer to my title is probably "yes, you bought the wrong brakes" but (a) which brakes should I have purchased or (b) what can I do to make these fit (c) anything else I should know about/consider?
12-22-08, 09:22 AM
Try switching the spherical washers around, so the thinner ones are on the inside. That will make the arms less spread out. I think the cable will straighten with a bit of use, and might need a bit of adjustment, but shouldnt affect the function.
12-22-08, 10:28 AM
Most modern canti and v brakes come with a set of conical washers containing one of each of the following for each arm: 1 X thick washer concave on one side flat on the other, 1 X thin washer concave on one side flat on the other, 2 X washers convex on one side flat on the other, one thin flat washer to be used between the nut and the conical washers...
The two convex washers must be placed diectly against the brake arm to form a sphere around which the convex washers can rotate. You can choose to put the thin or thick concave washers on the inside of the arm (brake pad side) in order to put the arm in a good position when the pad is against the rim. It sounds like your brakes came with the orientation that is less than ideal for your frame/fork. Swap the concave washers around so that the thick convex washers are on the inside and it should be better.
OH! And as far as I know, there is only one type/size/fit of canti brakes... if your bike has canti bosses on the frame and fork then you will probably be able to use almost any canti brake available (with proper adjustment). One exception might be very very old bikes or bikes where the wheel size has been changed (like from 27" to 700C), and in these cases you might need a brake with a little more adjustment range... but otherwise all should fit.
12-22-08, 11:02 AM
I recently installed those same brakes on a Soma DoubleCross.
Out-of-the-box, the fit was as you experienced.
After swapping the washers around, (as per the other postings here), this was the end result:
12-22-08, 01:15 PM
This was kind of hinted at in an earlier post, but to ask directly... Was the bike originally built for a different size wheel?
12-22-08, 01:53 PM
I should have mentioned! I already saw that the washers could be switched, and the thin washers on are already on the inside, and the brake-pad-holders are as far down in the slots as they can go.
Bike is a "Dave Marsh" Reynolds 532 Super Tourist, wheels are 700 but the rims do seem a bit wider than others I own, maybe 2cm wide rather than 1.8 cm or something around that. They don't seem bigger-enough to make a in the weird wire-slack. I have no idea if the frame was originally built for another size wheel -- the wheels are the ones I bought with the bike (2nd hand).
+1 Looks like you went from 27 inch rims to 700cms.
12-22-08, 02:30 PM
Okay, so if I have 700c rims, these are 8mm smaller than 27" rims (http://www.sheldonbrown.com/harris/wheels/630.html), which would make the brakes align on the rims properly, BUT won't the cable tension still be wack? And won't the brakes still run into the fork?
Also: I wouldn't be able to run fat tires with a larger rim, I think, which is/was the whole point of the bike =(
I've had this problem on an older cyclocross frame from the 1980s (700c, 126mm rear spacing). The canti studs on some older bikes are closer together than on modern bikes, not allowing a modern canti enough room to properly pivot down without hitting the tire before the rim.
The only solution that I found (after trying about six different brakes from my stash and the LBS) was to use an older set of cantis from 1994. I hope this helps.
12-22-08, 02:40 PM
Don't worry too much about the crossover cable, it's fine.
The issue with aligning the pads has to do with correctly positioning and rotating the pads on the arms before tightening the bolt. Loosen the bolt completely and you should be able to slide the bolt up and down in the slot in the arm. Slide it all the way down.
Next, you can grab the pad with one hand and rotate it up and down. Rotate it up/down so that the pad lines up with the rim. And rotate it fore-aft so that you have a slight toe-in at the front. Then tighten the bolt to clamp the pad in the desired position. Repeat for other side.
12-22-08, 03:39 PM
The pads are already jammed all the way down and rotated as much as possible.
Wrong size rim. I would start checking alternative cantis where the pads sit lower.
Apparently, bike was designed for 27 inch rims.
12-22-08, 10:18 PM
I think Ziemas is on the right track. I've had the same problem trying to use newer cantis on older bikes that have the bosses spaced closer together - brake pads contacting in the wrong spot and not enough clearance between the fork blade or seatstay and the rim. The newer brakes are designed with the assumption that the boss/pivot point is going to be farther away from the rim. As can be seen in your pictures, the brake arm would really need to pivot in quite a bit further before the flat surface of the arm would be parallel to the flat braking surface of the rim -- but it would line up perfectly if the boss was about 1cm further out the way they are built now.
I don't think the rim diameter is creating the problem -- the 4mm difference in height between a 27" and 700c wouldn't cause that much of a problem and should be within the range of adjustability of that long slot in the brake arm. You really just need one of the old brakes that are designed for the closely-spaced bosses that you have.
12-23-08, 12:27 AM
I had similar trouble trying to get a modern canti on an old touring fork. The bosses were placed much closer together than those on my modern fork (>1cm if memory serves). You might measure the C-C spacing of the bosses and compare that to a new touring or cyclocross bike in an LBS.
I had to use the older style "smooth stud" cantilevers since the pads can be pushed right up against the arm. Here's an example: http://www.ukbikestore.co.uk/Product/0/brct91mm/shimanoct91cantileverbrake.html
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