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Disk Brakes, Mechanical - What Am I Doing Wrong?

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Disk Brakes, Mechanical - What Am I Doing Wrong?

Old 10-11-19, 03:49 PM
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KC8QVO
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Disk Brakes, Mechanical - What Am I Doing Wrong?

I took my Disk Trucker brakes apart today and cleaned them thinking I could get some better stopping performance. After the clean I am not any better off. The brakes aren't in bad shape, they work OK but dont feel like they have the stopping performance they should have.

The bike has 3000-3500mi and the pads are the originals. Fronts roughly .1550" rears roughly .1560" for pad thickness. They seem to still have plenty of life left.

I used auto brake cleaner to scrub both rotors and pads. I used white ceramic grease for the spindles and bearings. I reassembled and got the calipers aligned again. I have the cables adjusted to where I have the brake lever actuation I want (IE - in place of closing the spindles on either side to take up slack - spindles are all the way out).

The pads in the picture are the rears. The fronts are the same, other than an extra thousanth of an inch wear.

Thoughts?
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Old 10-11-19, 04:19 PM
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1. Don't clean your rotors or pads. Doing so reduces braking performance until they bed in. It's also very easy to contaminate the pads so they do not perform well ever again. The only interaction rotors and pads need is low-grit sandpaper burnishing to reduce shrieking or some forms of shudder. Otherwise you should do nothing for the life of the pads, or the rotor.
2. A large portion of brake performance is in the housing. What are you using?
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Old 10-11-19, 04:37 PM
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Brake calipers are Avid BB7, road version, front and rear.

For what it is worth, my front brake was squealing a bit under light pressure before the clean. They operate squeal-free under any pressure now.
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Old 10-11-19, 04:52 PM
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Welcome to the wonderful world of getting mechanical disks to stop. Good advice mentioned above. I will add that oil contaminated pads can make stopping difficult, and all it takes is a greasy hand on the rotor or some over spray from lubing the chain. You can sometimes bake them to burn off the grease, simpler to replace.
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Old 10-11-19, 05:05 PM
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Well if I can get rid of the noise and maintain performance that is OK for me at the moment. As I said, they still work OK. They just dont stick enough to lock up.

One more question - how important are the rubber boots on the cables? All of those rubber parts have disintegrated and are no more.
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Old 10-11-19, 05:40 PM
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Originally Posted by Spoonrobot View Post
1. Don't clean your rotors or pads. Doing so reduces braking performance until they bed in. It's also very easy to contaminate the pads so they do not perform well ever again. The only interaction rotors and pads need is low-grit sandpaper burnishing to reduce shrieking or some forms of shudder. Otherwise you should do nothing for the life of the pads, or the rotor.
2. A large portion of brake performance is in the housing. What are you using?
I believe the question, "What are you using?" is meant to ask about the brake cable housing. Both gear and brake cable housing is a large factor in performance.
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Old 10-11-19, 05:47 PM
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Assuming those are metallic pads, maybe install resin pads. They tend to be quieter, and IME, provide a little better brake performance. The downside is that they wear faster, but with those brakes in particular, I think the pros outweigh the cons for installing resin pads.
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Old 10-11-19, 06:21 PM
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As for the housing, I am not sure. Everything on the bike is stock from the complete bike aside from the front rim and spokes, saddle, and accessories I have installed (racks, panniers/bags, computer, etc, etc), bottom bracket, and pedals. That includes the bars, brakes (entire set up - levers, cables, calipers, pads, rotors), hubs, and drivetrain (I only added to the drivetrain, never took anything away - crank and first 3x chain rings are stock). So I don't know what cables/cable housings are on the bike aside from what would have been on it as a complete bike build back in 2014.
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Old 10-11-19, 07:17 PM
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start here;

this is the best how to for BB7 I have found.also be sure your getting max contact pad to rotor.as for locking the wheel may want to try a metallic pad.https://www.jensonusa.com/Avid-Juicy...CABEgKZWPD_BwE
https://www.parktool.com/blog/repair...isc-adjustment

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Old 10-11-19, 08:26 PM
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Replace the cables and housings with new.
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Old 10-12-19, 01:54 AM
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If I wanted better stopping, I'd first assume that the pads are slightly contaminated and replace them, and clean the rotors before putting new pads on. My experience is that it's a waste of time to try to clean pads. If they're very recently and very slightly contaminated sanding can help, but otherwise they're pretty porous. Also it's helpful to properly bed the pads in anytime you have new pads, or if you ever resurface the pads or rotors. Basically, the idea is to drag a brake until it's warm, then perform a series of hard braking efforts with it that do not lock the wheel. This will evenly deposit pad material onto the rotor and improve brake performance. I would pretty much overhaul the entire bike before I got to lubing the caliper bearings...

Compressionless housing was probably not stock on the bike but does help a lot. You should have replaced cables and housing on everything by now if you've been riding since 2014.
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Old 10-12-19, 02:48 AM
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Taking a propane torch to your pads takes care of the porous issue.
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Old 10-12-19, 08:11 AM
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Have your brakes recently faded, or have they always seemed a little weak?

I recently adopted a road bike of similar vintage with mechanical disks. I was also a little disappointed at first, expecting to be able to easily skid the bike with one finger on the lever. I realized using mechanical calipers with road levers just doesn't give the mechanical advantage of hydraulics. I just enjoy the better qualities like being able to stop better in rain, and especially the freezing wet conditions we had in Colorado the other day--the cassette became a single-speed cone of ice, but the brakes worked great! I also appreciate getting the friction heat away from the plastic and rubber on the rim on long descents.
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Old 10-12-19, 09:12 AM
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Originally Posted by Canker View Post
Taking a propane torch to your pads takes care of the porous issue.
And the pad material. Pads are phenol-formaldehyde (PF) resin. In the case of “metal pads”, there are particles of metal embedded in the resin but the bulk of the pad is PF resin. PF resins are self-extinguishing which means that when the source of heat is remove, they stop burning but if you put a torch to them, they will burn until such time as you remove the torch.

Burning them with a torch won’t remove the oil that is contaminating the pad and will just burn up the pad. Might as well just through them out and start with new pads.
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Old 10-12-19, 09:38 AM
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Originally Posted by andrewclaus View Post
Have your brakes recently faded, or have they always seemed a little weak?
I can't remember how it felt when I first got the bike, but I've thought the braking performance has been a bit weak for a few couple years.

As for wet weather - I can still stop in the rain better on this disk set up than rim brakes, but the performance does degrade a bit in the rain/when wet.

At this point the bike is still fine to ride so I will likely leave everything as-is. If there were a bigger issue with a creased cable housing or pads that were worn down to zilch then I would start looking at replacing stuff. I'm just not there yet. I may reconsider this winter or next spring.
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Old 10-14-19, 10:30 AM
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What caused the odd wear on the pad laying on the stump? The brakes should be able to lock up the wheel even if you don't want that to happen in use.
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Old 10-14-19, 04:21 PM
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Picks of your whole set up?
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Old 10-14-19, 05:54 PM
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Originally Posted by KC8QVO View Post
I have the cables adjusted to where I have the brake lever actuation I want (IE - in place of closing the spindles on either side to take up slack - spindles are all the way out).
Is the rotor spaced as recommended by Avid?

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Old 10-14-19, 07:28 PM
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Originally Posted by davidad View Post
What caused the odd wear on the pad laying on the stump?
That isn't "wear", from abrasion. It is chipped. As to how it happened, I have no idea. I do not think it happened when riding but I suppose it could have.

Originally Posted by Leebo View Post
Picks of your whole set up?
I will see if I can get some tomorrow.

Originally Posted by cobba View Post
Is the rotor spaced as recommended by Avid?

Good thought. I didn't know there was a spec on the center, or lack-there-of, of the rotor between the pads. I just set the gap between the pads to where I had the brake pull at the lever that I wanted and the caliper assembly (both pads) is set so the rotor spins freely with 0 rubbing until I actuate the brake levers.

However, I can not imagine that this alignment is actually going to make any difference in the braking power. It might be "recommended" and it may affect pad wear over the life of the pads, but braking power - I sincerely doubt it. The pressure and contact area of the pads against the rotor will affect braking power. With as much pressure as gets applied to the pads I'd be shocked if such a small adjustment between where the rotor is between the pads is going to cause enough misalignment in the pad-to-rotor contact area to reduce resistance and decrease braking power.
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Old 10-14-19, 09:19 PM
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I had bb7s on one bike, you should be able to get the wheels to lock up however it does take a lot of lever pressure/travel almost back to the bars. I had to adjust mine after every ride. I finally chucked them and went hydro disc, like night and day difference.
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Old 10-15-19, 04:05 PM
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I have BB7s on 3 bikes, works great, little to no fiddling needed. OP,
you have a road or mountain brakes set up? It makes a difference. Need to make sure that
on the caliper side the pad sticks out enough. Pics?
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Old 10-15-19, 07:44 PM
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Here are some pictures, if they upload OK.


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Old 10-15-19, 09:35 PM
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Originally Posted by KC8QVO View Post
Brake calipers are Avid BB7, road version, front and rear.
Photos show that you have the BB7 Mountain version, what levers are you using?
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Old 10-16-19, 06:50 AM
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First, see if you can figure out what cable housing you have. If it is not compressionless housing, replace it with something that is, such as the Jagwire Pro stuff. It makes a big difference.

Second, if your pads are a few years old, they may have gotten contaminated at some point. I have sometimes had luck sanding them, other times not, and I just needed to replace them.

In 18 years of using discs I have never, needed more than rubbing alcohol to clean rotors. A few times I have removed them and used soap and water, though it was probably not needed.

Third, check out the how-too vids for set up. Setting up BB7s perfectly is a bit of an art as well as a science.
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Old 10-16-19, 07:42 AM
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Originally Posted by cobba View Post
Photos show that you have the BB7 Mountain version, what levers are you using?
This^^^^ Thinking that the lever pull is not enough. I have bb7's on my Karate Monkey, 180 front, 160 rear rotors. At 235 lbs, plus bike and gear, plenty enough stopping power. Replace the cables and housing, got metal ferrules at the end of the housing? And new pads.

Last edited by Leebo; 10-16-19 at 07:54 AM.
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