rms13

I just bought my first disc brake bike online and setting it up. It has Shimano BR-RS785 hydraulic brakes. Currently I'm getting rubbing on front and rear. I read the manual and watched a few videos. For the front I tried loosing the mount and squeezing the brake lever and tightening it back up (I can't squeeze the rear lever while working on the brake). I also tried positioning them both as center as possible. It seems like maybe the rotors aren't true but before I go and do anything crazy I wanted to see if I should be looking at anything else?

dsbrantjr

If the rotors are out of true you can carefully bend them with an adjustable wrench.

RubeRad

It's possible for rotors to be out of true, but it seems unlikely for new rotors.

When you are squeezing the brake with the mounting bolts loose, give the brake caliper a wiggle to make sure it is really floating to where the rotor wants it to be.

When you tighten the bolts, keep pressure on the brake, and tighten the bolts slowly, a little bit at a time on this one and that one, try not to move the brake by the action of tightening.

If all else fails, and you can see that the brake keeps returning, say, to the left, try loosening the mounting bolts just enough so that you can tap the caliper to the left. Eyeball the rotor through the calipers and try to get it so you can see daylight on both sides. Maybe increase the spacing by inserting business cards between the rotor and calipers on both sides.

Good luck!

rms13

Thanks. Seem to have the rear dialed in now

gsa103

Bent rotors usually show up as wobble. Carefully watch the distance between the rotor and a pad as you spin the wheel, if it's changing the rotor is a little warped, if its the same all the way around, the caliper is just off. Also, make sure you have the wheel positioned all the way in the drop-outs.

You can wrap a bungee cord or rubber band around the lever if needed.

Zef

Double check that the bolts or center lock holding the rotor to the hub are tight. For the rear brake, you can use a strap or large rubber band to hold the lever squeezed while tightening the caliper bolts.

CliftonGK1

If you've got the caliper centered and you're only hearing a shing-shing-shing sound as the wheel spins, then it's the rotor which needs trued up.
If you've got a contant scrape as the wheel spins, then the caliper isn't centered.

I use the squeeze and tighten method to do initial centering, and then fine tune them from there. Some brakes it's spot on, others... Meh, not so much.

rydabent

The simple fact remains, if the brakes are properly adjusted they do not rub.

CliftonGK1

Correct.
And everyone else offered suggestions of what to look and listen for.

stevoo

Fairly simple. The squeeze method gets u close. Then carefully look into the caliper to see the rotor to pad gap. Carefully adjust the caliper mounting bolts as needed to center it.
Rotate the wheel while looking at the gap and split the difference between left and right gap. Look at the leading edge of the pad and the trailing edge of the pad. The gaps need to be equal there as well. The pad gaps need to be parallel for no rub as well as centeted.

You will know you have it right when you squeeze the lever and the pads move the same before making rotor contact and the rotor does not move at all when applying the brakes. You can easily see this while looking into the caliper from above while applying the brake.

It will be obvious if the rotor needs attention.

Sometimes you have to loosen the bolts one at a time just enough to carefully tap the caliper into position then tighten.

First few times may take you some time but stick with it.

Good luck.

Zef

While not necessary, I found that a tool like this, coupled with squeezing the lever while tightening the caliper mounting bolts, speeds up the centering process quite a bit. I don't have this particular model as it was not available at my LBS here in southwest Belgium, but the nominal amount I paid for the one I did get has been well worth it:



-j

ellen87

ok fix man

JonathanGennick 

Thaaaat's gonna cost me. Just threw it into my shopping cart at Jenson.

rms13

thanks everyone. I have them spinning rub free now. But I notice the brake pull seems different. I have to pull the rear lever further than the front lever to engage the brake. Is that a result of set up or should I be adjusting the lever?

joejack951

Air in the system?

fietsbob

Hydraulic , yea Bleed the brakes to get any air Out.

For Mechanicals? Could be a result of all that extra housing and cable length
between your handlebars and the rear Disc caliper..

I use the 2 extremes in my speed dial levers adjustment range,
to soften the front response of the BB7 Mountain discs ..

(Using my Bike Friday commute/utility, in this Wet Town.)

stevoo

Be aware you have free stroke and reach adjustment on them.

Andy_K 

I've got the same brakes and the same issue. My current experience is that the front and rear are performing about the same (equal grab, equal modulation) within my abilities of perception, but lever for the rear brake ends up noticeably closer to the bar with a full squeeze. Is that what you're seeing?

I've bled them several times. I also did the thing where you zip tie the lever overnight and then top off the fluid in the morning. That actually made a pretty big difference.

One theory that I've read is that the hose is flexing (very slightly) and because the hose for the rear is considerably longer it makes a perceptible difference. Shimano ships this brake with the flexier BH59 hose, supposedly because they think it has more of a "road" feel. I've read that some people are switching these out for the BH90 hose that comes with the XT M785 brakes.

Personally, I think it's more likely that there's a tiny bit of air still in the system. For me, it's working well enough that I'm in no rush to get out the funnel and syringe again. I'll probably double check the free stroke adjustment, because that's easy and I was playing with that before I did the zip tie thing, but I think it's something else.

stevoo

At the end of the bleed process apply slight pressure to the syringe at the caliper and then pump the lever really fast many times.
I have found this dislodges the last bit of air.
Even my tandem has super stiff lever after doing this.

Yes, bh-90 hose wotks good. Have switched to this on a few bikes eliminating the inline coupling too.
Same size OD but thicker wall. Does not kink as easy. Good stuff.