I have been having problems with the rear disk brake of my brand new Surly LHT. First the pads would catch so I had them adjusted. Now it has poor performance and a loud grinding/cruching noise while using it. It also brakes irregularly offering a bumpy ride. The wheel spins freely now so I don't think its the pads.I have sent it in to the shop but they insist the brakes are fine. The front brake works flawlessly though. And now I have noticed what looks like scraping on the edge of the rotor. That would mean that maybe the rear rotor is warped but its a brand new bike.

Now I have no idea what to do.
The brakes are Sram BB7 mechanical disk brakes.

Brand new bike bought in a Bike shop they should help you fix it.

I have. They just told me something vague about "Rear brakes having a different feel then the front". I guess I will bug them again so they will not fast talk me this time. They might of assembled the rear brakes wrong.

Is it possible for the metallic part of the brake caliper to scrape the rotor? That's the only explanation I can think of in my limited experience.

did you look? or is speculation over the internet how you solve things?

back off the pad adjustment , does it go away?
re alignment is simple.. Hold the brakes ON while you loosen and tighten again the caliper post mount bolts ...
make sure wheel always seated the same?


I liked the 2nd set of pads* I put in my BB7 a lot better than the stock ones..

* a Kool Stop Organic compound the back disc Avid..





....

"scraping on edge of disc"... like, ummm, the OUTER EDGE? as in: not the braking surface?

the caliper may be TOO close to the disc... seen it before... makes a nasty GRINDING NOISE.... which can be intermittent due to frame and axle flex, wheel position, trueness of hub, etc.

go back to that shop, and point out the wear on the outer edge of the disc.... if they don't show concern, leave shop, report shop to Salsa, go elsewhere.... figure out how to shim the brakes out further from the disc... won't take much, maybe a washer or four.

Avid disc post mount uses the spacers that are also used on V brake pads, so easy to come by ..

Thanks. I will try to adjust the pads and the mounting. If that does not work I will have my bike shop recheck the caliper position.

You could take it back to the shop, but eventually you're going to need to learn how to adjust your brakes on your own. I am constantly fiddling with my BB7's to keep them working right, and I never have been able to get exactly the same lever feel on the front and rear.

First thing to check is to make sure the pads are seated in the caliper properly. It's possible to get them in, but not in all the way, and they'll work but grind like you're describing. I would pull the caliper so I could get a good look at the pads and make sure they are in there right. Whatever you do, don't get your grimy fingers on the pads or the rotors or you will never be able to get them to stop squeaking. After you are sure the pads are in there right, put the caliper on and follow these steps:

Make sure that the caliper is centered. Loosen the caliper bolts enough so that the caliper can move about. Loosen off the cable bolt too and make sure that the cable tension adjustment on the brake lever is all the way in. Use the pad adjustment knobs to back out the pads all the way. Now turn the inner pad adjuster all the way in as far as it will go (though don't force it). Then back out again by 10 clicks. Now turn the outer adjuster in until the caliper is locked against the brake disc. Tighten the caliper mounting bolts. The caliper will now be centered properly. Now pull the cable tight and secure it with the cable pinch bolt. I like to pull the arm up a little bit before tightening to make sure it is tight. Now back out both the pad adjustment knobs all the way.

Pull on the brake lever to make sure that there is no slack. There should be no play at all in the lever. As soon as you start to pull there should be movement on the caliper arm. If there is play then you will need to pull the cable through a bit more and re-tighten it.

Now turn the inner pad adjuster inwards 4 clicks and pull the lever a couple of times and spin the wheel. Keep repeating this until you can hear rubbing on the disc. Now back out the adjuster one click at a time until no rubbing can be heard. Then back out by another one or two clicks for clearance.

Repeat those steps for the outside pad adjuster.

there are bike repair books to read Lennard Zinn wrote some, he also writes a column in Velo News every issue..