xlDooM

Hey guys.

My recently acquired 29er came with Shimano BR-M446 hydraulic disc brakes. This is my first bike with disc brakes. I've always been hesitant to make this switch, because:
- v-brakes work great for me, I never ride through significant mud so the braking power is ample even downhill;
- I've noticed every bike with disc brakes I've ever riden had slightly draggy pads;
- the argument I always get is that disc brakes are maintenance free, but surely if you can tie your shoes you can adjust a v-brake?

Lo and behold, the brakes tend to drag ever so slightly when it's wet and dirt gets onto the rotors. I've adjusted the calipers so they are nicely centered, doesn't help. I've pushed the pistons further inward with some sheets of paper, but they auto-adjust so after braking a few times they just make some noise again. It's not that I feel any resistance, but I hear them zing and it annoys me. Anyone have similar experiences?

DiscTruckerMF

Im new to mtb and most of the info I have found is that cheap hydraulic brakes are a no no. Ive been using avid bb7 mechanical disc brakes on my touring bike and they work great. BB7 has a really nice dual adjusting system and the mounting brackets have a nice positioning system. IT's funny, I've heard people swear up and down that any hydraulic disc brake is better than mechanical but honestly, not true at all. my bb7's modulate great and have plenty of stopping power.

I see the brakes you have are deore level and quite frankly, the consensus I've seen is to go with SLX level at a bare minimum and picking up some used XTs would be ideal. I initally put some elixir 5's on my new 29er build and they seemed to be find but then I came across a deal on some used XT 775 brakes and they seem to be great, I do not have any of the issues that you mention and the modulation is much better than the elixirs which were very much on or off.

Daspydyr 

The Zing would annoy me as well. I like my bike to ride quietly. Try asking this question in the Mechanics thread. You should be able to set up drag free. But as Disc Trucker points out, the quality of compnents make a big difference.

rs98

I have the same problem with my Tektro Novela mechanical disc brakes. I was able to make the noise go out from the back but it keeps coming back in the front. Coming from V-brakes, I like the feel of the discs.

jimc101

Have the brakes been bedded in? if not, that could explain the lack of power.

When you say you acquired the bike, was this 2nd hand or new, if 2nd hand, you don't know the history of the brakes, were the rotors or pads ever contaminated? Do they just need a bleed?

For being cheep, no Shimano hydraulics normally fall into this category, that's normally for unbranded, for maintenance, like any new thing, the first few times you work on them will take a while, after a couple of times, a full bleed of a brake is a 5 minute or less job.

xlDooM

The bike was new. The brakes have not really bedded in I guess since I haven't done any long downhill rides, but I also have no complaints about the power. As with any bike I've owned, I can lock up the wheels at will. They also feel tight and smooth. Do you think a bleed might make a difference to the dragging? I kinda fail to see how that would affect it, but it can't hurt I suppose.

Since it only happens when it rains (so larger dirt particles can stick to the rotors easily), I was assuming it was a general problem with disc brakes having such fine tolerances. They are about the cheapest hydraulic shimanos though, perhaps the more expensive ones with servo wave get around this by having a wider gap but a more aggressive lever? I smell an upgrade in the future.

DiscTruckerMF

there are great deals to be had on brakes right now at blue sky cycling https://www.blueskycycling.com/cat-brake-disc.htm They don't include the rotors but you said your bike is new, the rotors being warped shouldn't be your problem. Looks like they have slx for $70 and xt for $100. Well worth considering, especially since you can probably easily fetch $75 for your pair on craigslist or ebay

agent pombero

I have been extremely pleased with the Avid BB7s on my Surly.

xlDooM

@DiscTruckerMF: Thanks for the tip, I'm in Europe though, not sure there's a big market for used disc brakes where I live, and shipping would probably kill that deal you posted I'll be on the lookout though.

I'll have a look at the Avid range too. I never really considered it.

Lexi01

I recently switched from V-brakes to disc. My bike came with the 596 series...so still a lower end Shimano brake.

First time I had to use them with any force I nearly went over the bars. A lot of stopping power.

I doubt the 446 would be THAT much worse than my 596s.

I'd take the bike into a mechanic and get him to verify there's nothing wrong with them.

ColinL

That's a Deore hydraulic brake. Not bargain basement, but not high-end either. Centering the caliper fairly frequently is a fact of life. Loosen the mounts slightly, on the mount to fork / frame side, and squeeze the brake. Carefully tighten the bolts without moving the mount. Viola! Centered pads.

I have Avid BB7s on one of my bikes. They are fantastic mechanical discs, but as a total package they are not significantly better than the OP's stock brakes IMHO. They do have the ability to adjust easily without moving the mount, true, but they also take more lever effort.

Bedding in the pads is very easy and should be done for sure. It's not too late.

Lexi01

Pretty sure the 596 is only 1 step up from the 446 and the 446 is also hydraulic - so not sure of your point.

dexmax

I had this problem when the brakes were new.. Mine were even worse, it would vibrate at the slight touch of the pads..
It eventually (gradually) went away, in less than 50kms of riding.

xlDooM

Hmm we'll see, yesterday they were pretty quiet. The bike has 120km on it now, but I don't do a lot of braking on my rides. I sorta bedded in the front one (meaning I gave it a half assed effort and quit when it wasn't really increasing in bite power) and that one is quiet, so I'll do the rear one properly tonight. If it stops snowing that is, don't want to bed in the rear brake on a snowy road

krobinson103

I have 12,000km on my Deore hydrolics and have changed the pads 3 times now. I have zero complaints. They will run super quiet, super smooth for a long time. They do get a bit noisy if it rains, but thats a fact of life with any hydrolic brake. So do XTRS.

ColinL

I was replying to the thread in general and not your post about the 596.

Grimlock

Try putting a better, internal-cam QR (Shimano style) on front and back. They hold tighter and should reduce the flex that is letting the rotors touch. This is exclusively a setup issue. Bring it to a shop if you can't figure it out. Don't sell your brakes- the parts aren't the problem.

allroy71

I didn't see it mentioned, but have you check how true your rotor is? If you the rotor has a spot where it keeps hitting the pad, it is easy to try and bend the rotor in the other direction.
https://www.parktool.com/blog/repair-...d-installation

You don't need anything fancy, just a crescent wrench can do it. It is easier on a truing stand with a rotor gauge, but you don't really need that either.

xlDooM

I bedded in the rear brake. I checked the rotor, it is true, no sideways movement that I can spot from the gaps at the caliper. The front brake seems to be permanently quiet now, the rear is usually quiet but when I've sloshed through a puddle it will make noise for up to 100m afterwards. It is better when I use the rear brake a lot, but I drive mainly on flat pavement and hardly ever need the rear brake.

Here's what I think happens: when you don't use the brake a lot, the pads creep ever closer to the rotor, because they are self adjusting. If you give a good tug on the lever, they retreat a bit again, but I don't typically do that with the rear brake. So the pads end up very close, and any dirt that splashes onto the rotor will catch the pads and zing until it's thrown off again. I don't think the parts or the setup are at fault.

It seems servo-wave equipped brakes are better at this because they have greater pad clearance.