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Old 06-22-06, 12:02 PM   #1
geedubbayoo
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How do I toe in Mafac cantilevers?

(I posted this to Classic & Vintage yesterday but no replies or even views. I think this might be a more appropriate forum.)

I replaced a set of Mafac pads with Koolstop salmons and they squeal horribly. (It's strange that the Mafac pads didn't give me this problem even though I installed a previously unused set. I suspect it's because they're made of a softer material. That's one reason I replaced them; while they did a fine job stopping the bike they seemed to wear quickly.) I've lightly sanded and cleaned the rims and sanded the pads but it hasn't helped much. I think I need to toe in the brakes but I'm not exactly sure how. Twisting the arms of sidepulls with a wrench is simple enough but these cantis are different animals.

Would you bend the posts of the brake pads? I don't have access to a vice so that's going to be tricky. Plus I'm afraid of weakening the posts or snapping them in two if I have to refine the bend a second or third time.

Would you use a wrench to twist the round part of the brake arm where the pads insert? Seems like that might be easier...the taper of the area just below the round part (looks like the "waist" of an hourglass) might make it easier to bend. However it's going to be a pain because I'll have to take the brake arms off the frame so I don't accidentally bend the mounting posts. I'll also have to remove the brake pad because the screw head will get in the way and won't let me get a good flat contact between wrench and brake. Seems like a very inexact and inefficient method...I can easily see getting it "not quite right" after all the disassembling and reassembling.

I can see how Paul Neo-retros are an improvement in this design with their vertical adjustment slots and the fact that they use brake pads with spherical washers.

Thanks for any advice you can offer...this bike is currently unride-able.If there's anything else I should consider (or any steps I might have missed above) please speak up!
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Old 06-22-06, 02:15 PM   #2
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You could sand the pads towards the rear. This would have the same effect as toeing them in.
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Old 06-22-06, 04:08 PM   #3
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Cantis usually have beveled washers where the brake-pad posts are held that lets you angle the pads. Doesn't look like it on that picture you posted. So... just sand the pads on the rear a bit and that'll be fine.

Last edited by Mothra; 06-23-06 at 01:14 PM.
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Old 06-23-06, 07:51 AM   #4
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OK, time for the older guy to speak up.

As you suspect, these brakes are toed-in by gently bending them. More amazing, Park makes a tool especially for this:

http://www.parktool.com/products/det...t=14&item=BT-3

(really designed for road-type calipers but will work for cantis as well).

Just go easy and you will not bend the posts; better yet, just throw these away.

I've always hated Mafac brakes...
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Old 06-23-06, 08:01 AM   #5
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^^^^^^ universal brake toe adjustment spanner. Precision calibrated for all styles and systems. Accept no substitutes.

Some models include a wedge of wood that the untrained eye could easily mistake for a doorstop, which is used to brace the caliper arm against the fork so you bend only the arm and not the brake spindle. Even an old canti post is probably stout enough that this isn't a concern, or you could put it in a vice to do the actual adjustment.
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Old 06-23-06, 09:34 AM   #6
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Quote:
Originally Posted by Landgolier


^^^^^^ universal brake toe adjustment spanner. Precision calibrated for all styles and systems. Accept no substitutes.

Some models include a wedge of wood that the untrained eye could easily mistake for a doorstop, which is used to brace the caliper arm against the fork so you bend only the arm and not the brake spindle. Even an old canti post is probably stout enough that this isn't a concern, or you could put it in a vice to do the actual adjustment.
I was going to make that exact post! Complete with the adjustable wrench! Good on ya .
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Old 06-23-06, 11:32 AM   #7
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i cant belive park even makes such a silly tool... you can also get new pads.
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Old 06-23-06, 11:48 AM   #8
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In defense of the park tool (and I don't defend park very often), it does give you a good leverage angle, and it fits on there without taking the wheel or the pad off, which isn't guarnteed with an adjustable wrench. Not worth it for the home mechanic, but I can see it for a shop.
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Old 06-23-06, 01:16 PM   #9
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The thing with bending the calipers is you should do it just once. Eventually the pads will wear flat and squealing will happen again. Do you then bend the calipers even more? Every single time the pads wear flat? No, after that first time, the pads will wear at an angle relative to the backing-plate. When the surface gets parallel to the rim, you just flip the pads 180-degrees and you'll have toe-in again.
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Old 06-23-06, 03:00 PM   #10
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Quote:
Originally Posted by Mothra
When the surface gets parallel to the rim, you just flip the pads 180-degrees and you'll have toe-in again.
That's if the sides of the rim are perfectly vertical. Otherwise, you'll have to change them side for side.
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Old 06-25-06, 04:45 PM   #11
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Quote:
Originally Posted by Landgolier


^^^^^^ universal brake toe adjustment spanner. Precision calibrated for all styles and systems. Accept no substitutes.

Some models include a wedge of wood that the untrained eye could easily mistake for a doorstop, which is used to brace the caliper arm against the fork so you bend only the arm and not the brake spindle. Even an old canti post is probably stout enough that this isn't a concern, or you could put it in a vice to do the actual adjustment.

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Old 06-25-06, 07:22 PM   #12
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Originally Posted by Mothra
The thing with bending the calipers is you should do it just once. Eventually the pads will wear flat and squealing will happen again. Do you then bend the calipers even more? Every single time the pads wear flat? No, after that first time, the pads will wear at an angle relative to the backing-plate. When the surface gets parallel to the rim, you just flip the pads 180-degrees and you'll have toe-in again.
Actually, the reason for toe-in is to cause pads to wear evenly from the beginning. If you don't toe them in, the forward motion of the rim as the pads touch them causes their heels to dig in while the toes lift up, causing them to wear unevenly and not be maximally effective. So it's just the other way around - if you don't toe them in, your brake pads will eventually wear flat. The idea of toeing in is to avoid this period of less-than-maximum braking and squealing, which can be worse if the entire surface of the pad isn't contacting the rim.
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Old 06-25-06, 07:30 PM   #13
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Do not toe in the pads by bending the brakes. Toe in the pads by filing the pad material so it is toed in, which means you take some off from the back to the front at an angle.
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Old 06-25-06, 07:45 PM   #14
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Why? That's an awful lot of work considering that you can do this in two minutes with a wrench and a good eye. If you're concerned about safety, bending the brakes a wee bit isn't going to weaken them worth squat, even if it's done several times over the entire period of ownership.
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Old 06-26-06, 12:06 AM   #15
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Quote:
Originally Posted by grolby
Actually, the reason for toe-in is to cause pads to wear evenly from the beginning. If you don't toe them in, the forward motion of the rim as the pads touch them causes their heels to dig in while the toes lift up, causing them to wear unevenly and not be maximally effective. So it's just the other way around - if you don't toe them in, your brake pads will eventually wear flat. The idea of toeing in is to avoid this period of less-than-maximum braking and squealing, which can be worse if the entire surface of the pad isn't contacting the rim.
This slop only happens with low-end brakes that have a lot of play in the pivot. Yes, such wobbles will drag the pads forward and twist them so that the leading-edge will wear out faster. Yes you can bend the brakes so that the extra toe-in will counteract the wobbles and have the trailing end touch first. But after a while, the pads WILL wear so that the surface is parallel to the rim. What then? Bend the brakes again and again? Eventually, you'll have brakes that are bent 20-degrees with the pad-surfaces parallel to the rim.
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Old 06-26-06, 07:34 AM   #16
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No, as grolby first mentioned, the pads only need to be toed in at first installation to minimize grabbing and squeal. They will tend to wear more on the leading (back) edge and maintain optimum toe-in throughout their life.
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