JunkYardBike

I've experienced brake chatter using cantilever brakes and have found successful solutions. However, I've never experienced it on a road bike using conventional sidepulls..until now.

The setup is short reach Dura-Ace 7400 calipers and 7401 levers, Kool Stop black Dura type insert pads in Tektro holders, Mavic G 40 hard anodized rims, Dura Ace 7400 headset.

The rims are hardly worn, but I have noticed there is more wear on the sidewalls at the spoke holes. I've seen photos of rims with this same wear pattern, but never read that it causes brake chatter.

Other observations:

1) I swapped the Kool Stops out for cheap Tektros, and the problem is reduced to some degree. I've found Kool Stop to be more grabby than other pads, but the Tektros stop like crap.

2) I over-tightened the headset and the problem persists.

3) The springs in the Dura Ace calipers are extremely strong, so maybe this amplifies the problem?

4) The chatter only occurs at 'terminal' speeds. I can ride at a good speed and it will slow without chatter until I am nearly at a stop.

I've thought of gluing some emory paper to some pads and 'breaking in' the rims a bit (at a safe speed in my driveway).

Other thoughts?

Ira B

Make sure there is no side play in the hub bearings.

You may need to very slightly bend the arms so the front edge of the pads contacts the rim ever so slightly before the rear edge. If the rear most end of the pads contacts the rim first they can chatter like crazy.
To do this remove the pad and use a small adjustable crescent wrench to slightly bend the pad mount flat area.

Before doing this I would remove the calipers and make sure the double jam nuts that set the pre-load on the pivot point are adjusted properly.
Loosen them. Apply a single drop of 30w oil at the pivot point. Tighten the inner nut until there is no play in the arms but the caliper still moves freely. Tighten the outer jam nut. Reinstall.

Make sure the pads and rims are clean by wiping with automotive brake parts cleaner.
I recommend against the emory paper idea.

JunkYardBike

Yeah, I was wondering if the emory paper would be stupid.

I should add a few other things:

1) The calipers are perfectly adjusted: they move freely with no play. The spring tension is what is strong - they are notorious for this. Nothing is sticking.
2) No play in front hub. It is adjusted with a tiny bit of play which is eliminated once the QR is secured.
3) I'm using adjustable Tektro holders, so toe-in has been set - to the extreme. I assume the rear of the pads only hit at 'terminal' stop, which is when the chatter occurs.
4.) Everything is spotless on the bike, as I've just built it up. I cleaned the rims and pads several times with rubbing alcohol.

FBinNY 

The primary cause of break chatter, especially at lower speeds is a grab/slip process at the brake shoes, compounded by twisting of the caliper arm/

When you apply the brake the forward motion of the rim pushes the shoe forward twisting the brake arm so the shoe digs in at the heel. At a critical point the shoe slips back, and the process starts anew. This is why we toe in the shoes slightly, and/or use shoes with longer tails. At higher speed the frequency is higher and we get the characteristic brake squeal, at lower speeds you get shuddering.

Increasing pad friction improves braking, but worsens squeal and shudder because the twisting forces are higher compared to the correcting force of brake pressure.

There's no single perfect solution, but the following help. Clean rims, increasing toe-in, long tailed shoes, and filing a shallow bevel on the rear of the shoe eliminating the corner which digs in - not recommended for those who ride in the rain because it worsens water wipe-off.

You can sometimes improve things slightly by changing how you modulate braking. Avoid that medium brake pressure where the effect happens using more or less braking pressure depending on circumstances. Sometimes more brake on only one wheel works better than lower force on two.

JunkYardBike

That makes sense, given the problem is worse with the Kool Stop pads, which are designed to increase water wipeoff and have an additional 'lip' built into the tailing edge of the pad. I'll try sanding that down a bit to see if things improve.

I suspect the rim may also be contributing, based on the strange wear pattern which suggests the sidewall flares ever so slightly at each spoke hole (I type 'rim holes' above, possibly misleading).

Although I understand all calipers will flex, I'd be surprised if the 7400's are a major culprit. These were top of the line and designed to be stiff.

The fork, on the other hand, may be contributing. It's a custom frame (not built for me) from the 90's built with lightweight Columbus tubing. Maybe the tubing is too light for my weight (190 lbs) or the fork was designed poorly.

Ira B

I would be surprised if it was the fork. I weigh 200 lbs and have ridden lighter forks with side pulls and never had a problem.
From the sound of it the only suspect left is the pads. I would try a different kind.

Drew Eckhardt 

Or just adjust the pad holders where the mounting is adjustable (as with Campagnolo brakes).

FBinNY 

Rereading the details of the OP, I think the place to look might be the rims.

Hard anodized aluminum is a low friction material. As the brake track begins to wear through to the base metal at the spoke holes, there will be alternating bands of low and higher friction, which can cause pulsing. You don't notice it at higher speeds because the frequency is too high.

JunkYardBike

Currently, the only wear through the anodized surface that is showing any silver is at spoke holes, and it is very light. At the spoke holes the anodized surface is still intact. That's why I asked about the emory paper, thinking it might help to eliminate the slick anodized surface.

FBinNY 

On the first and last pair of hard anodized rims I ever owned, I ended up sanding off all the hard surface. I did it by making 4 strips of emery cloth with holes at one end. Mounted them under the shoe mtg bolt, bringing them around the back of the shoe and gluing them to the surface. Then rode circles a parking lot gently dragging the brakes, alternating front and rear, and resting them to cool often. Voila, one of the first pairs of rims to have machined brake tracks.

After that I went back to my preferred lightweight silver anodized tubular rims, getting lower weight, longer service life and better braking, all at lower cost.

BTW- my commuter with standard non-anodized rims sometimes shudders a bit just as it comes to a full stop. I'm perfectly willing to live with that, and see no reason to shorten the rims' service life with sandpaper.

JunkYardBike

I could probably live with the shudder, too, but it was disconcerting to experience after the great care I took building up the bike...for 2.5 years! I'm a bit of a collector, and this is a "Sunday bike" so I'm not overly concerned about the longevity of the rims. They won't wear out any time soon.

I haven't ridden it far, but with the short test runs I've made, the shudder has decreased in frequency. I imagine as the rim wears more, it will become a non-issue, but I was looking for ways to speed that process and other theories on what may be happening.

As to hard anodized rims, I'm sure your experience wasn't unique. I've read numerous accounts of the process causing rims to crack prematurely, too. Any wonder they don't produce them any longer?