Road Bike, Cycling Forums banner
1 - 20 of 28 Posts

·
Registered
Joined
·
78 Posts
Discussion Starter · #1 ·
Hi all.

The outside brake pad (left in the image below) on RS685 hydraulic disc calliper doesn't sit parallel to the face of the rotor. This is reducing clearance and leads to light rubbing at high disc temperatures. Any idea how to fix it? Both pads are just a few weeks old and true. I've tried several spring as I have a bunch of them from old pads.

Note: it's really hard taking a picture of this clearly, but the rotor is parallel and centered to the rotors if you look at it dead on. The image makes it look like it's very close to the right hand edge.

Metal Tool accessory Steel Aluminium Musical instrument accessory
 

·
'brifter' is f'ing stupid
Joined
·
15,565 Posts
1) Clean your bike.
2) Get a pad spreader and reset the pistons.
You may have to 'work' the pistons a bit to get them even on both sides but that should help. You've already tried multiple springs so you've ruled that out.
 

·
Registered
Joined
·
78 Posts
Discussion Starter · #3 ·
1) Clean your bike.
2) Get a pad spreader and reset the pistons.
You may have to 'work' the pistons a bit to get them even on both sides but that should help. You've already tried multiple springs so you've ruled that out.
Thanks for the reply, cxwrench

Pistons themselves (and the pads - at least on the back) are fully clean, serviced and lubricated with brake oil; they move in and return perfectly and symmetrically. System is bled, it does not leak and travel and bite are spot on. Issue exists before and after the service so I'm as confused as heck. I tried two other return springs last night and poked them around with a screwdriver to see if I could force different orientations but no change. I note (and I don't think this is relevant but mentioning anyway) that the spring does not sit under the little raised bumps on the back of both pads on both sides at the same time... it always sits slightly on the piss, one side or the other. But I can't see how this can possibly make a difference as it's the arms of the spring themselves that press on the pads.
 

·
Registered
Joined
·
78 Posts
Discussion Starter · #4 ·
1) Clean your bike.
2) Get a pad spreader and reset the pistons.
You may have to 'work' the pistons a bit to get them even on both sides but that should help. You've already tried multiple springs so you've ruled that out.
Actually by "pad spreader" what are you referring to exactly? Just checking in case I don't understand something. For "spreading the pads" I used a large plastic tyre lever. Is that the kind of thing you mean?
 

·
Registered
Joined
·
456 Posts
You may also want to see if resetting the caliper on the bolts will fix the issue as well. Loosen both caliper bolts, grab the lever with firm pressure so the caliper/pads grab the rotor. Then while still holding pressure tighten the bolts back up on the caliper.
 

·
Registered
Joined
·
1,449 Posts
You may also want to see if resetting the caliper on the bolts will fix the issue as well. Loosen both caliper bolts, grab the lever with firm pressure so the caliper/pads grab the rotor. Then while still holding pressure tighten the bolts back up on the caliper.
I was thinking down this road too. Seems like the simple answer is adjust the positioning of the caliper.

If the brake is functioning properly, clean, etc. and one pad ends up closer to the rotor than the other, why not just adjust the caliper?
 

·
Registered
Joined
·
20,781 Posts
Both pads are just a few weeks old and true.
What do you mean the pads are true?

Is this your first time replacing the pads? Did this problem not exist before (or you didn't notice)?
Maybe it's always been this way and the original pads wore in and corrected the problem.

It's possible the caliper mount needs facing and the caliper isn't sitting parallel to the rotor. There's a tool for this.

 

·
Registered
Joined
·
78 Posts
Discussion Starter · #10 ·
What do you mean the pads are true?
That is to say, there's nothing funny going on with the pads. The backs are flat, everything's straight, not bent and so on. I.e. to the best of my eyes, they look good.

Maybe it's always been this way and the original pads wore in and corrected the problem.
That's actually possible. Whilst I have replaced them before, I didn't get much life out of the replacement pair because I contaminated them when cleaning the bike (I covered the rotors, but when I pulled the cover off it dropped some gunk/oil. gah!). Unfortunately I've thrown away the originals so I can't check them for uneven wear.

----

So... anyway... I've fixed it and I don't know how precisely.

Out of desperation I started from scratch, going through the whole routine. I.e. remove; clean callipers and pistons; clean pads with isopropyl alcohol; clean the mounts; lube and reset the pistons; mount and align the callipers; and finally balance the pistons so they met in the center. And now everything's fine.... I don't know which one of those steps fixed it I'm afraid.

Regarding cause, the only other thing I can think apart from what @tig said is that the non-drive-side piston was coming out at a slight angle (???) One of my pistons was quite stiff in the past so maybe it was this one and maybe something was causing resistance in one area thus causing it to protrude slightly skewed. I could, of course, be talking out of my behind as I'm definitely no expert! :)

Anyway, all is well. Thanks for the help!
 

·
Registered
Joined
·
20,781 Posts
I don't know which one of those steps fixed it I'm afraid.
I hate when that happens. :(
Ideally it's best to eliminate items one at a time. But sometimes you just want to get it solved and starting from scratch is easiest.

If everything is good and the pads are parallel to the rotor, then the mounts are probably ok. You probably just had a misaligned piston.
 

·
Registered
Joined
·
78 Posts
Discussion Starter · #12 ·
I hate when that happens. :(
Ideally it's best to eliminate items one at a time. But sometimes you just want to get it solved and starting from scratch is easiest.

If everything is good and the pads are parallel to the rotor, then the mounts are probably ok. You probably just had a misaligned piston.
Yeah, me too. I feel a bit sheepish about it as I know how important having clear answers is to people googling for this kind of thing. But on the plus side if anyone finds this thread in future they will see that it's probably solvable if they do all the steps above :)
 

·
Registered
Joined
·
1,287 Posts
Again, just gotta say... know how long that would take to fix with rim brakes? About a minute. Hope all that awesome modulation is worth it. :)
 

·
Registered
Joined
·
760 Posts
You may also want to see if resetting the caliper on the bolts will fix the issue as well. Loosen both caliper bolts, grab the lever with firm pressure so the caliper/pads grab the rotor. Then while still holding pressure tighten the bolts back up on the caliper.
I've done this numerous times and still have a similar problem to the OP. The brakes work perfectly and quietly and if I use them lightly there are no problems, but if I use them with any real force, then for a few seconds after I release them I get a ticking and howling sound. I "think" its the pads vibrating in the holder and the disc warps a little when hot, after a few seconds it goes away. I found i had to eyeball the rotor to be centered in the caliper and it is fine after that. Positioning the caliper while squeezing the brake makes perfect sense, but for me, it doesn't work so well for some reason.
 

·
Registered
Joined
·
78 Posts
Discussion Starter · #16 ·
Again, just gotta say... know how long that would take to fix with rim brakes? About a minute. Hope all that awesome modulation is worth it. :)
Funny you should say that, but a few weeks ago I was seriously considering selling my bike for something with rim brakes - if only to save 700g. I even went so far as test driving a SuperSix Evo (Dura Ace, Ksyrium alloy rims) but whilst it is an astounding bike the rim brakes are a big step back for me - especially during the light rain I tested it in. So yes, I do thing it's worth the occasional problem... In the same way Di2 is worth the occasional "I really should have charged the battery" moment ;)
 

·
Registered
Joined
·
78 Posts
Discussion Starter · #17 ·
I've done this numerous times and still have a similar problem to the OP. The brakes work perfectly and quietly and if I use them lightly there are no problems, but if I use them with any real force, then for a few seconds after I release them I get a ticking and howling sound. I "think" its the pads vibrating in the holder and the disc warps a little when hot, after a few seconds it goes away. I found i had to eyeball the rotor to be centered in the caliper and it is fine after that. Positioning the caliper while squeezing the brake makes perfect sense, but for me, it doesn't work so well for some reason.
Squeezing the lever doesn't work at all for me either.

My process is to align the rotor as perfectly as possible within the callipers at both ends with the pistons withdrawn (there are tools to help you with this: Hayes make one but I do it by eye). Then I pump the lever to move the pistons in. If one advances faster than the other I hold it back a bit whilst advancing the other so they come in equally. Sometimes it's hard holding it so I shove in a couple of rigid business cards behind the pad to act as a spacer.

Regarding the noise, it seems most likely that - assuming your rotor is perfectly in the center - your pistons aren't advancing evenly. At least that's been my experience.
 

·
Registered
Joined
·
78 Posts
Discussion Starter · #18 ·
Actually, one more thing. It dawned on me last night when working on the pads that in their "pushed back into their cylinders" position there's maybe 0.5mm (the curved bits) protruding from the surface. Is that a sign the system could be over-filled? Or do they not bottom-out perfectly flush to the surface?

They look like the following image from www.epicbleedsolutions.com, maybe a tiny tiny amount further out.

View attachment 316368
 

·
Registered
Joined
·
1,287 Posts
Bad enough when we have to chase down mysterious ticking/clicking noises with a carbon frame. You guys want to add mystery brake problems to the mix????? Seems pretty nuts to me but to each their own I guess. Again, I can't think of a single rim brake problem that can't be fixed in less (often much less) than 5 minutes with at most one simple tool. I'm assuming you know about the principle of KISS - with an emphasis on the final "S?"


Sent from my iPad using Tapatalk Pro
 

·
Registered
Joined
·
5,062 Posts
Bad enough when we have to chase down mysterious ticking/clicking noises with a carbon frame. You guys want to add mystery brake problems to the mix????? Seems pretty nuts to me but to each their own I guess. Again, I can't think of a single rim brake problem that can't be fixed in less (often much less) than 5 minutes with at most one simple tool. I'm assuming you know about the principle of KISS - with an emphasis on the final "S?"


Sent from my iPad using Tapatalk Pro
these are not mystery problems. We have been managing this in mtb for years. ParkTool even has a tool that will take care of this as CX has pointed out.

I had a set of Magura Martas that needed this piston reset every couple of months.

Call this the toe thing you did with calipers. Or at least you don't have to clean the brake track on rotors like you do with caliper brakes.
 
1 - 20 of 28 Posts
Top