Metal in pads, how concerned should I be that the rims are damaged?
 

Hello:

My Surly LHT (stock build) has about 3000 miles on it, and I am quite ashamed to just now have changed the brake pads. The picture shows what I found on the existing pads. These were the stock Tektro pads and I have replaced them with Kool-Stop salmon pads.

In examining the rim, it _seems_ to have plenty of brake surface left .. .in fact I cannot see where this metal came from. How do people measure the amount of brake metal left on a rim?

Thanks for any hints.

The metal shavings you see in the pad are fairly common, and not by themselves an indicator of anything.

If the rim looks fine it probably is, but you can get a better idea on some rims because they have wear indicators. Not all these rims have these, but look for small, shallow holes or dimples, or a machined groove in the rims braking surface. If you have any of these, the rim is designed to be safe until worn ro where they disappear. Otherwise you can also get a sense of the wear bu feeling the sides of the brake track for a ridge where it's unworn. Rims vary but the wear allowance is typically 1-2mm, so there's quite a bit that can come off.

Otherwise, if you don't see anything, and there are no deep gouges which an embedded stone might have cut, odds greatly favor that the rim is fine. In any case, rims rarely fail suddenly due to track wear. There are usually early warning signs such as measurable bulging in areas which causes pulsed braking (dirt, or oil films can also cause pulsing), or hairline cracks forming at the line where the unsupported tire flange meets the braced part of the rim. If you see any of these cracks, or if the rim clicks or creaks when inflating tires failure is imminent.

You asked about the rim. but showed the pads ..

to be accurate a thickness measurement of the new rim would need to have been taken , where the brake track Is ..

then a more recent measurement again , to actually have the Data to Judge/quantify rim wear.

the bead hook gets in the way , so the caliper would be notched , or a piece that fills in behind, inside the rim is kept and used again .

As the rim wears , so as to maintain the record of the same test conditions.

Dental caliper:

http://ecx.images-amazon.com/images/...JL._SY300_.jpg

Thanks! Never seen/heard of that.

Anyway I see that there is plenty of 'meat' left, so I I think I'm good. Now the new pads squeal horribly, but that's a topic for another post. At least they actually stop the bike, the Tektro even when NOT worn out were kind of terrible.

It was a good move to replace your pads with Koolstop ones as they are made of a much softer material than the Tekto ones. Give better braking as well.

Maybe not, but on this ride I didn't feel anything unusual until about 8 or 9 miles after I started. At about 20 miles in, things went bang: rites042
(Sorry, John, I didn't measure the rim thickness.)

http://home.comcast.net/~jeff_wills/...s/rites042.jpg

From the picture... it looks like the wear marks are gone. 3K miles isn't [all that] much for a brake pad. It's the dirt and grit that gets between the brake pad and the wheel that wears off all that metal from the wheel and rubber from the pad.

I try to wash the dirt and grit off the surface areas.... and I use a little scrubby [like for dishes] to clean up the brake pads. The pads and wheel might last a bit longer if kept clean... maybe. But they certainly do stop better when clean.

The Tektro pads on my bikes have those bits of metal in them too. They were literally destroying my rims and so I got rid of them off one bike and will soon do so on the other bike. Koolstop pads seem to be the best way to go. For one thing they are consistent and you know what you're getting. Also when you hit the picks, you do not hear that scraping sound letting know your rims are being torn to pieces.

fmt_biker and 009jim, do you happen to have grooved rims ?
From my experience, the metal chips stuck in the brake pads come from the rim itself, and 90% of the time its a factory grooved rim (like sun UFO, for example). I saw it on many kinds of brake pads, and when it happens the brakes produce an awful noise and (as you already mentioned) deteriorate the brake performance. If you pry out those metal chips the brakes will get back to its original performance, but only for a short period of time (until new metal chips will get stuck).

*my very first message :) excuse me for any grammar/vocabulary mistake, as English is not my first language.

The metal in your pads is galled metal that the pads roll up off the brake track then break off when they become embedded in the pad faces.

With those bits stuck in the pad faces you now most certainly have big ugly gouge marks in your braking track on the rims. Those grooves are where the metal in the pads came from.

It seems like the bigger the rider the easier the cheap Tektro and Shimano pads pick up and gall like this. Likely because us heavier riders have to use more lever pressure to stop. As a result at the first sign of this I toss those style pads and put on Koolstop or other brands that I know won't gall the metal in the same way.

And best of all the "fingernails on the chalk board" sound that the bits of metal in the pads make will be gone with the pads. Contrary to some folks the pads are not supposed to sound like rubbing two slabs of steel together with gravel between them.... :D

i've decided that most of that stuff is coming off the rim due to the machining of the braking surface. they do a pretty coarse machining job and the ridges start coming off and imbed in the brake shoes after a few hundred miles. i pry it out with a knife if it refuses to work it's way out on it's own or before my patience is exhausted. it may happen a few times then they all wear off enough that it never happens again. only had it happen on machined braking surfaces.