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Old 05-11-08, 09:49 PM   #1
RT
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Brake maintenance: Disc vs. Rim

After spending my afternoon on a bicycle maintenance mission, I have come to validate a personal conclusion regarding ease of brake maintenance.

Discs are a Godsend.

Having not replaced pads on my 2005 Fuji Sagres since the purchase of the bike, I was frustrated to have taken five times the amount of effort to replace and adjust said pads, when it took me all of five minutes to install and adjust the disc pads on my 2003 Giant Rainier (Avid BB5).

The issue I am having with the linear brakes on the Sagres is that I can't seem to loosen the pads from the rim. After installing the new pads, I even had to release the cable and re-fasten it looser than it was before. The pads still rub the rims. There are small adjusting screws on one of the brake arms, and on the shifter. I have consulted Sheldon's brake pages, and will go back to square one tomorrow, but am frustrated by what seems to be a simpler system becoming more complicated.

All I want is to deploy the quick release on the linears, swap out the pads and re-engage the quick release. It doesn't seem to be that easy. From what I've seen so far, I'll have to remove a washer or two in order to release the pads from the rims.

Can anyone direct me to a resource other than Saint Sheldon's pages? His pages are quite thorough, but I did not find my answer there.
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Old 05-12-08, 11:33 PM   #2
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Not sure I understand the question, but I will take a try at it.

When you change out the pads, the new pads will, of course be thicker than the old pads. If the new pads are a different kind of pads, then they could ba a lot thicker than the old pads.

So, it makes sense that you would have to release some of the cable to accommodate the new pads.

Of course, brakes have a maximum open position, so if your rim with plus the thickness of the brake pads is too great, then you are outside of the maximum allowable for those brakes.

I hope this helps.
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Old 05-13-08, 12:03 AM   #3
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Factors that change over time with linear brakes:

The wheels go out of true
The pads (or pad cartridges) can move
The linear springs lose effectiveness, go out of balance or both
The bushings become contaminated or dry

Try these things:

Unhook the linear spring from the back of the brakearm pin and bend it out slightly. Repeat with the other spring until the arms retract equally. Unscrew the small adjusting screws all the way, using them only for fine adjustments (Hint: You can also loosen them to balance the springs).

After replacing the pads and loosely assembling the hardware, grab the brake lever with one hand. With the other, loosen the brake pad nut, manually position the shoe where you want it on the rim and tighten just snug while simultaneously holding pressure on the lever. It should be positioned very close to where it needs to be. Make minor adjustments with hand pressure, then tighten the nuts down. Screw in any cable adjusters all the way (or optionally a couple turns out to aid in wheel removal) and adjust the cable length.

If after bending the springs the arms still don't retract, pull the mounting bolts, clean the posts and grease them. Assemble again and test.

Inspect the brake cable, replace or lube.

While I agree that cable discs are easier to maintain than linear brakes, both are easier than cantilevers.
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Old 05-13-08, 12:38 AM   #4
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Thanks fellas! I think I have enough to go on now.
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Old 05-13-08, 01:34 AM   #5
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If after bending the springs ...
Why bend them? At the base plate of the arm there usually are 3 holes that acts as anchor points for the springs. Pull the arms, move spring anchor point one hole down for stronger spring action, reassemble.

Sus forks may have a moveable base plate. Loosen assembly, move base plate to lower spring anchor point, tighten and reassemble.

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...pull the mounting bolts, clean the posts and grease them. Assemble again and test.
The arms do not slide around the posts, they slide around an integrated bushing that's immovably clamped to the post.
Lubing the posts doesn't do anything for brake performance, but it'll act as rust prevention and can make future removal easier.
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Old 05-13-08, 03:44 AM   #6
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Originally Posted by Toddorado View Post
..I can't seem to loosen the pads from the rim.
Will the pads clear the rim if you pull the arms apart by hand? In that case you haven't got enough return spring action.

Or don't you get the pads to clear the rim even if you pull the arms apart by hand? In that case you need to set the bits up with some more mechanical slack - either by clamping the wire down further out or by restacking the washers.

As already pointed out - your new pads are thicker than the old, so that has to be dealt with. Maybe you're even using another brand of pads this time?
Depending on how worn your pads were and what earlier adjustments have been made you might get away simply by turning the barrel adjuster in a few turns. The barrel adjuster is the knurled screw with a locknut that the brake wire runs through right at the lever. Turning it in will effectively lengthen the brake wire(increase pad/rim distance), turning it out will shorten the wire.

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.. I even had to release the cable and re-fasten it looser than it was before.
That's one way of doing it, and there's nothing particularly wrong with it either.
Next time, have a look at how the barrel adjuster is set first though.

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.. The pads still rub the rims.
Then it's really beginning to sound like you haven't got enough strength in the return spring, or that your brake wire isn't moving freely in its sleeve. For a bike that hasn't had a brake overhaul since 2005 the latter is quite probable.
Best is to start by checking that everything is moving freely before you start tinkering with the return springs.
The "bulletproof" fix would of course be to replace both the brake wire and the sleeve. The're cheap enough but you might still get away with less.
Release the quick release, then unhook the brake wire at the lever. Does the sleeve move freely or does it stick? Now shoot some wd-40 or similar product into the brake wire sleeve and move the sleeve up&down along the slack you've created. Add more spray, move and check for improvement. Do the same for the noodle(the 90-deg bend down by the brake QR). Noodles come with a plastic liner that sometimes gets jammed up. If the liner looks like it's trying to get away from the noodle you probably need a new one.

NOTE: brake wires should either be CLEAN, or very lightly lubed. A flush like this is really a bodge, and particularly not recommended for a bike that's ridden in cold conditions.

Pulling the wire out of the sleeve for a wipedown and a light lube is another option. But doing that carries a risk that the end will fray making reassembly impossible.

Once everything seems to be moving freely it's time to reassemble and check for improvement.

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Originally Posted by Toddorado View Post
..There are small adjusting screws on one of the brake arms,
But that one is usually only used when the brake arms aren't clearing the rims symmetrically. If neither is clearing the rim you've got another problem.

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Originally Posted by Toddorado View Post
..There are small adjusting screws on ..the shifter.....
That one is used to set the brake levers resting position, i.e. distance from the bar. If you've tinkered with it before turning it all the way out will lengthen the wire.

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Originally Posted by Toddorado View Post
.. ...All I want is to deploy the quick release on the linears, swap out the pads and re-engage the quick release.
For me it's usually:
- turn barrel adjuster in
- unhook brake QR
- switch pads
- hook up brake QR
- turn barrel adjuster out a few turns.
But then I'm using cartridge pads, which does away with some of the uncertainty of brake pad thickness.

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Originally Posted by Toddorado View Post
.. From what I've seen so far, I'll have to remove a washer or two in order to release the pads from the rims.
If extending the cable didn't sort it out, then removing washers won't do it either. Sticking wire or weak return springs is more likely what you should be looking at.
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Old 05-13-08, 04:45 AM   #7
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Hey, thanks for the tips. I am familiar with all the parts and locations you spoke of. I'll check the return springs and measure the old pads with the new to see how much of a difference there is in width. I did try to make adjustments with the barrel adjusters turned all in, and the cable is moving freely. I think it's just a matter of getting the old stock pads off and adding a new, better set of pads.
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Old 05-13-08, 08:55 AM   #8
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Quote:
Originally Posted by dabac View Post
Why bend them? At the base plate of the arm there usually are 3 holes that acts as anchor points for the springs. Pull the arms, move spring anchor point one hole down for stronger spring action, reassemble.

Sus forks may have a moveable base plate. Loosen assembly, move base plate to lower spring anchor point, tighten and reassemble.
Why not? It takes seconds rather than minutes, requires no tools, is entirely effective and is the only recourse if the brake does not have all the features you assume are on every type, yet the spring has still bent with usage.


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The arms do not slide around the posts, they slide around an integrated bushing that's immovably clamped to the post.
Lubing the posts doesn't do anything for brake performance, but it'll act as rust prevention and can make future removal easier.
Perhaps the one type of brake you are used to is that way, but the vast majority of OEM brakes out there pivot on the post. If it does use a bushing, the advice to grease is equally valid.
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Old 05-13-08, 10:59 AM   #9
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...the only recourse if the brake does not have all the features you assume are on every type.
Go back and re-read, I said usually.
I suppose it's possible that there are brake posts w/o ANY adjustment feature for the return spring anchor point, but I've never seen one. On what make of frame/fork would they be found?

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.....the vast majority of OEM brakes out there pivot on the post.
I've run everything from Avid Ti's to dirt cheap noname almost-plastic cantis, and they've all had a bushing pressed into the arm.
Think about it, if they did pivot against the post itself then how hard you torqued the arm retaining bolt down would be critical to brake performance (or you'd have to mess around with shims and washers to get the fit right) and that just isn't happening, not to me, and not that I've ever heard of.

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.If it does use a bushing, the advice to grease is equally valid..
Greasing the post can't hurt, but a thick grease won't do the moving surfaces between the arm and the bushing much good. It'll have to be something lighter like an oil to get there.
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Old 05-13-08, 11:13 AM   #10
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Work on a few department store bikes...you'll see plenty of awful crap.
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