nyc_commuter

I recently noticed that the disc brake rotors on my 2009 Valencia bend when I apply the brakes/calipers. I have a feeling the rotor will gradually warp as I continue to use the brakes and rubbing will occur eventually. I was wondering if anybody else had the same problem with these disc brakes: according to Trek's website they are Shimano M416. Veteran LBS mechanic fiddled around with it and told me that there's nothing he can do; Shimano just makes crap disc brakes at this price point. He recommended I upgrade to Avid BB7's. I know the Valencia is by no means a high end bike w/ high end components, but I think it's a little ridiculous that a major component requires replacement within less than a year of purchase and with less than 1000 miles on it. I am waiting on Trek Customer Support to see what they can do for me, but in the meantime I would appreciate any feedback from other owners of this disc brake as well any general disc brake adjustment tips you can offer. Thanks!

CCrew

BS that theres nothing he can do. The M416's have slotted mounts, and the stationary pad is adjustable to boot. The most that the rotor should flex is the amount of air gap set between the stationary pad and the rotor. Basically no more than a paper thickness. BB7's are the gold standard for mechanical brakes, but the M416's work just fine. If they were Promax'es like they're putting on some new Trek's I'd say trash them.

Good procedure to learn to do yourself anyway. Here's the instructions.

https://techdocs.shimano.com/media/te...9830696761.pdf

dynaryder

Replied over in the Hybrid forum.

M_S

Disc rotors are designed to flex when force is applied, it's part of how they work. BB7s would certainly be an upgrade, but not because the rotors don't flex. Now, them getting warped means they may be bending too much, or the rotors might be cheap. That does not mean you need to get new brakes, you can just get new rotors.

Now, the more relevant question is whether the bike stops/slows effectively. if the answer is yes, then you have nothing to worry about.

How long does it take for the rotors to become significantly out of true? Bending them back is not very complicate dor hard, so if it's like once every 100 miles I wouldn't consider it a big deal.

dynaryder

Wat? I've got well over 8k miles on my Safari,and I've never trued the rotors even once. If you're truing the rotor on a street bike with any kind of regularity,you're either banging the bike into things indiscriminately,or something's really wrong with your brakes.

nyc_commuter

CCrew: Thanks for the link to the manual. I'm gonna take a look this weekend.

M_S: The brakes work fine and the rotors are still true, but my concern is that they will warp eventually since the rotors are flexed/bent every time I apply the brakes. I just wish it were possible to set up the brakes so that I wouldn't have to bend back the rotors every 100 miles. If they are in fact designed to flex, then that implies that they won't become warped with continued use under reasonable conditions. Hopefully, I can adjust them this weekend so that they don't flex with the help of the Shimano manual. Thanks everybody for your input!

jeph

I'm not familar w/ the Shimano M416, but I have Avid Juicy 7's on a mtb and it sounds like the caliper is not adjusted correctly. On mine, I loosen the caliper bolts spin the wheel and grab the brake lever. Don't let go of the brake lever and tighten the caliper bolts down. This should hopefully cure this.

You might make sure that you wheel is correct in the drop outs. I bent a rotor once when my skewer slipped.

You might search the MTB forum as disc brakes are very common over there these days.
Good luck.

Jeff

nyc_commuter

I wrestled with the brakes all day to no avail. One problem I found was that the inner pad on the front brake is not parallel to the rotor: the top edge of the pad (edge closest to the center of the rotor) is angled toward the rotor such that it touches the rotor before the bottom edge. To a certain extent, I think this is how the M416 is designed. The spring is on the bottom edge, so the pad clamps down like a V shaped trap instead of coming down evenly. Because the "slanted" inner pad takes up extra space, this leaves less room to adjust the outer pad, and as a result, the only way I can keep the outer pad from rubbing is to slacken the cable so much that it takes a full squeeze to apply any kind of meaningful pressure to the rotors - which, btw, still flex when the pads touch. I think at this point, I will bring it into a different shop to see if they can adjust it better than me or the first shop. Thanks again for all your help.