Noisy braking

[j beede]

I have replaced my brake pads with wood blocks to which I will glue sand paper. I plan to sand both braking surfaces at once using this setup. Anyone ever tried this? I am wondering what grit paper to use. My front rim is pretty deeply grooved so I am leaning toward fairly coarse paper. Maybe 120 or 200 grit?
...j

[KDC1956]

Sounds like you need a new wheel.I don't think its a good idea to do what you want.I may be wrong but if its that bad I would ask someone at your LBS first.

[Bill]

:O ermmm... I never heard of that method, but I am sure someone has. Just as a funny... "Don't try to use them as regular brakes while riding ." lol.

[j beede]

I think the carbon front fork amplifies the braking noise--ticks, pops, clicks, etc. The rear rim's braking surface isn't much smoother, but seems quieter during braking. My Shimano rims have "thickness" indicators in the braking surface. I intend to sand down the braking surface without going past the indicator. Replacing the rim sounds expensive. I see lots of bikes with nasty braking surfaces... I wonder why resurfacing is not a more common issue.
...j

[Bill]

To be quite honest, wheels are really thin as it is. When you sand down the surface you are changing the engineering (believe that's the word) of the wheel. Not too sure of the resurfacing procedure?? I have a wheel building book I am reading currently, I'll see if there is a reference.

[j beede]

By inspection you can see that the manufacturing process machines the braking surface, I suspect the wear indicators are used by the rim manufacturer to control how much material they remove. I will contact the rim maker to see what they say. Based on my chat with the LBS it sounds like buying new wheels would cost about the same as having them rebuild my wheels with new rims. May be time to learn to build wheels.

[Joe_W]

No, the wear indicators are so that you know when to replace the rim. Sand down to it and you can throw away the rim. I'd only sand down the high spot at the joint a bit, so the ticking stops.

[Bill]

Interesting Joe. Thank you I really did not know that.

[j beede]

I see no reason why the rim cannot be re-cut, like the rotor in a disk brake, to restore the surface. If this cutting removes material to, or below the bottom of the wear indicator then the rim is scrap. If the braking surface is planarized and the wear indicator remains, then I am good to go. This is like shaving racing tires to improve radial runout. Obviously the process is sacrificial, I'm okay with that given the alternatives.

[jr14]

(01-20-2010, 01:50 PM)j beede Wrote:  I see no reason why the rim cannot be re-cut, like the rotor in a disk brake, to restore the surface. If this cutting removes material to, or below the bottom of the wear indicator then the rim is scrap. If the braking surface is planarized and the wear indicator remains, then I am good to go.

Technically, you are correct, and yes it is sacrificial. Very sacrificial. You are reducing the life of the rim by a LONG time by machining them down. And rims are nothing like brake rotors. That's like comparing apples to dump trucks. Rims are usually aluminum, so they're soft. Brake rotors are MUCH harder metals, usually steel. So you can get away with machining down a tad.

Your first thought was the right one. Sand them. Go really course to fine in 50 grit increments down to...oh...600 grit, and you'll have a nice sticky rim for the brake pads. The last time I did this was a while ago, and at least I THINK it was 600 grit.

If you machine the rims down, you'll be learning how to build wheels in NO time, because those rims will be scrap, really fast.

Good luck!

[j beede]

Technically you are incorrect as anodized aluminum (Rc~80) is quite a bit harder than steel (Rc50~60). Of course the hardness of the aluminum is really due to the nanolayer layer of Al2O3 formed at the anodized aluminum surface (which admittedly is pierced rather quickly). Actually, my braking surface project is not so sacrificial as I view the rims as scrap the way they are--even though the wear indicator is still visible. I have looked at some used rims over the past few days and see that I am not the only one with nasty braking surfaces. It surprises me that cyclists put up with this. Stickiness I am not interested in... quiet braking during early morning rides is my goal!
...j

[jr14]

(01-22-2010, 09:38 PM)j beede Wrote:  Technically you are incorrect as anodized aluminum (Rc~80) is quite a bit harder than steel (Rc50~60). Of course the hardness of the aluminum is really due to the nanolayer layer of Al2O3 formed at the anodized aluminum surface (which admittedly is pierced rather quickly). Actually, my braking surface project is not so sacrificial as I view the rims as scrap the way they are--even though the wear indicator is still visible. I have looked at some used rims over the past few days and see that I am not the only one with nasty braking surfaces. It surprises me that cyclists put up with this. Stickiness I am not interested in... quiet braking during early morning rides is my goal!
...j

I'm not going to have a metallurgical discussion over this, but steel is hard all the way through, while aluminum, as you point out, only has a very thin layer on top of the material that is harder than steel. The rest is soft.

And since they are already viewed as scrap, try slate. It might work. I called a friend, and he suggested using slate to resurface the rim, giving it a really good surface to grip to.

And when I said "sticky", I was referring to a nice surface that the brakes would want to hold on to. Sorry for the confusion.

I really do hope this helps. Good luck! Let us know how it turns out.

---

Well, I'll be damned! I looked this up right after I posted, and this popped right up! http://www.instructables.com/id/bike-rim-resurfacing/

Looks like my friend might be on to something.

Note: I have NEVER tried to resurface a rim with slate, but it does make sense.

[j beede]

Here's an update... I ended up using a small, precise pine cube as a sanding block. I used medium emery cloth then progressively finer wet paper to restore the braking surfaces on my Shimano rims. I used a Sharpie to fill in the wear indicators so they were easy to see/monitor. I was able to planarize both sides of the wheel with no perceptible change in wear indicator depth--I removed the high spots, radially above and below the brake swept areas, then just took off a tiny amount past that. Brakes are now renewed, strong and sound great. Wheel gleams like new too. As a bonus for covering myself with aluminum particles I got a "toy" wire welder out the deal (used to build the wheel sanding/truing rig).
...j

[jr14]

Wow. Did you take pics or video? There are some folks (Like ME for example) that would love to see the process. Maybe you want to do it to the other wheel?