chis51hd

I'm wondering if the rotor should be perfectly centered in between the brake pads. When I had the brakes installed at the lbs, the mechanic positioned the caliper so that the rotor was closer to the inboard pad (closer to the rear wheel). Then I tried spinning the wheel and noticed that the rotor was slightly rubbing the inboard pad. He said it would go away after the pads were broken in. After my expected break-in period I noticed the pads were still rubbing, and the wheel wouldn't spin for very long when I put my bike on a stand. So I decided to add shims, and center the caliper over the rotor. After I did that, there was no more rubbing, but I felt that the rear brake wasn't as strong (before I adjusted it). Did I do something wrong? Any suggestions would be most welcome!

Btw, I'm using M.O.B. mechanical disk brakes (very similar in design to Shimano mechanical disk brakes).

bi-King

When you have mechanical disk brakes, normaly (all models I know) only the outside pad moves, the inner pad is fixed, so when you hit the brake the rotor bends a litle bit. So the disk caliper is normally tuned in the way that the rotor stays more close to the inner pad, in this way the rotor will bend less.

now that you have the rotor in the center, you can see this clearly, hit the brake slooly in order to see the rotor bend a litle bit.

why you fell less power in the braking?
The pads and the rotor are a kinematic pair, so when you move one of them most probably is that you have to ride a while till they are a perfect match again.

I used to ride with mechanic disk brakes long time, and I used to put it the more close to the inner pad as possible, without rubbing it, and still they bended a litle bit.but that was the way that I tunned them up, the most close to the inner (fixed) pad.

born2bahick

I agree, even some low end hydro's use a single piston/ fixed pad setup, Hayes So1e, for example.

Raiyn

Yes you did. Put them back to the way the mechanic set them. The way you have them set now you're bending the rotor excessively due the fact that the outer pad is the only one that move and it presses the rotor into the inner pad and not getting the proper rotor contact .

chis51hd

Okay, I'll try adjusting it again. I'm just curious because the rotor doesn't actually bend, and it seems like the caliper design lets both pads move inward when you brake. Anyway I'll try to remove the shims I added and see what happens. Thanks for the inputs, guys!

seely

If its a mechanical and both pads move, I really want to know what brake that is!

Raiyn

The IRD Dual Banger operates in that manner. I'll be sticking with my Avid's thanks.

As for the rotor "bending" in mechanical systems the rotor does flex towards the inner pad. You want to keep it to a minimum though.

bi-King

rst produces ones quiete a long time, I think more than 3 years. altough it moves the 2 pads they were less efficient braking than my old formula md-1 that moved only on pad.

chis51hd

The brand is M.O.B., which stands for Men On Bikes, it's made in Taiwan. It's a pretty good copy of the Shimano mechanical disk brake, except that it can't be installed on a Manitou fork (only one set of mounting holes). I'll try to post a picture anyway. I've already adjusted it so that the rotor is closer to the inboard pad (it also moves, but less than the outboard pad). It already gives decent braking - at the moment anyway.

concernicus

when using mech disc brakes, the pads should be at a 2:1 ratio over the rotor. that means that the inboard pad (pad closest to the wheel) should be twice as close to the rotor as the outboard pad. so, when adjusting the brakes, dial out the inboard pad once for every two times you dial out the outboard rotor. your LBS had it right. it is perfectly normal for the pads to be uneven

chis51hd

Thanks for all the advice. I think my brake adjustment is quite close to the 2:1 ratio thing. Here are some pictures for you guys.

ppc

There is something else that impacts braking power with mechanical disc brakes: if you don't line up the pads exactly parallel with the rotor, the brake will feel mushy, not very powerful, and you'll have a hard time getting rid of rubbing noises when you adjust the lever. The usual method to ensure the pads are well aligned is to move the inboard pad closer to the rotor one or two notches, apply the brake, tighten the calliper down then move the inboard pad back away from the rotor.

chis51hd

I just recently upgraded my crappy disk brakes to Avid BB7s, and they're awesome. They're also very easy to set up and adjust. I just have a question about pad spacing. I know that with mechanical systems you're supposed to set the inboard pad closer to the rotor than the outboard (moving) pad, so that the rotor doesn't flex that much during braking. But according to Parktool.com repair tips (and the Avid site), it's the other way around--inboard pad is further from the rotor. What's the deal?

ppc

Setting the disc closer to one of the other pad is usually nitpicking, unless you have a very wide gap between the pads, which would happen only if you don't true the rotor and you're trying to get rid of chaffing noises, and even so you won't hurt the rotor, it doesn't really bend all that much. With a rotor that's good and true and a well aligned caliper, you can set both pads very close to the disc surface and the bending will be minimal during braking. For what it's worth, I center the rotor between the pads, and the gap between the pads and the rotor is a hairline (I need to shine a flashlight on the other side to see it).

Old Hammer Boy

If you look at the Avid installation manual, you'll see that they recommend a 2:1 ratio, with the inboard pad the closest. What I do is adjust the inboard pad until it rubs, then back it off 2 or 3 clicks. Then I adjust the outboard pad. It's really quite simple.