Help with rubbing hydraulic disc brakes

[NHAero]

This is the third I've tried replacing the not-so-great Road BB7s on my Anderson. I've tried TRP Spyres and also the Juin Techs, but couldn't ever get them not to rub the rotors, especially on the fork. The rotors are true - the BB7s never rubbed, but they have conical washers that help with slight misalignments.

This time around I'm determined to make this work. I bought a single wheel's worth of TRP hydros (caliper is same front and rear) to see if I had better results with a full hydro. First I removed the pads and seated the pistons back in the bores. After a bit of fussing, i could get the rear to work with no rubbing.

I shifted to the front. Rubbing, plenty of it. Careful inspection revealed that the ISO adapter may have slight misalignment due to a small ridge of paint, which I carefully removed with a utility knife. Using the typical technique of loosen caliper bolts, squeeze brake lever, then tighten bolts, didn't work to center the caliper - the inner pad was always rubbing. I ended up using a 0.014" feeler gauge on the inside pad while clamping the caliper against the rotor and tightening the bolts, and eventually I got the pads to run free and not rub.

I squeezed the lever a few times, still good, then progressively the rubbing came back. It looks like it's worse at the top of the pads so I put thin washers to set the caliper out a bit, and tried again. I got it to not rub, but after several cycles of squeezing the lever the rubbing comes back (the caliper and adapter bolts BTW are being set with a torque wrench to spec.)

I think that the rotor is fine and that the alignment is OK, because I can set things up to not rub initially. All I can think of now is that the pistons gradually move inward as the lever is squeezed - they're not fully retracting.

Has anyone solved this type of problem? Might the TRP caliper be more prone to this than Shimano calipers? The hydros on my mountain bike seem to work fine, and when I replaced the pads I had to push the pistons back but it all worked.

Any of your experience would be appreciated! Thanks

[moose8]

I don't know the answer, but I know when I was having issues with a hydraulic trp brake I emailed them and they were super prompt and helpful in figuring out the issue (too much fluid in my case). So emailing the manufacturer might help if you have a day or two to wait.

[NHAero]

Thank you, great suggestion.

[zank]

It is aways best to machine the post mounts true. I do that on every frame and fork that leaves here. You would be amazed how far off a new fork can be. Are you in southern NH? If so, it's not too far a drive to central MA if yoir local shop doesn't have the tools.

[NHAero]

Thank you for your help. The fork has an ISO tab rather than post mounts, so there is an adapter in between. If I can't get this sorted out I may well make an appointment to visit you in Sutton - I'm on Martha's Vineyard and it would be a treat to meet you and see your shop.

.It is aways best to machine the post mounts true. I do that on every frame and fork that leaves here. You would be amazed how far off a new fork can be. Are you in southern NH? If so, it's not too far a drive to central MA if yoir local shop doesn't have the tools.

[zank]

I'd love to have you. We can true the rotors with my dial indicator fixture too. We'll get it set.

[NHAero]

Imam still trying to understand why it appears Incan get the set-up to not rub but yet repeated squeezing the brake lever starts the rubbing again, That seems to be a piston retraction issue?

[Fatty]

Imam still trying to understand why it appears Incan get the set-up to not rub but yet repeated squeezing the brake lever starts the rubbing again, That seems to be a piston retraction issue?

That's what it sound like to me. You should be able to eyeball it and see if the pad/piston is retracting. Set up using two feeler gauges, one under each pad, business cards work fine as well. If you really want to geek out Hayes sells a shim tool to set the pads.

http://www.jensonusa.com/Hayes-Brake-Pad-and-Rotor-Alignment-Tool

http://brimages.bikeboardmedia.netdna-cdn.com/wp-content/uploads/2009/10/hayes-caliper-tool-interbike-01.jpg

[Peter P.]

Please educate me on disc brakes.

I thought one pad was fixed and only one moved. The idea was the moving pad flexed the rotor, pressing it against the fixed pad.

[vqdriver]

Not with hydros or dual piston mechs.
Only the old school mech discs, a la bb7

[RowanB]

In my experience with MTB discs, it's better to align the calliper to the rotor with pads out. I don't find the squeeze the lever then tighten the calliper bolts technique to work very well.

[benb]

Probably depends on the brake.. my Hayes the "loosen bolts, squeeze lever, tighten bolts" procedure works very well. I don't have that tool although I am tempted to get it. (I have most of the other Hayes tools)

Sometimes this can be pad material selection too although I get the impression when you're not talking MTB they don't even have pads that need heat to stop making noise. With MTBs it seems like if you go with the more downhill oriented pad and use it for more X/C type riding you will get noise from the pad not getting up into it's working temp range.

[ergott]

One thing I did wrong with a brake setup was to not have a washer on top in between the bolt and the caliper. The brake would keep returning to the same position after I tightened it even though I was centering it to the rotor. Once I put washers on the bolts (standard, not cupped) it allowed me to tighten the bolts without shifting the position of the caliper.

[45K10]

Are you getting the rubbing before you bed in the pads? If so, try bedding them in and then putting the bike back on the stand to check for rubbing.

[NHAero]

Yes, this is in the workstand still.

Are you getting the rubbing before you bed in the pads? If so, try bedding them in and then putting the bike back on the stand to check for rubbing.

[arthurlo]

With the hydraulic system, they have a built in "self-adjust" feature to compensate for pad wear. Ideally, both pistons will move in evenly toward the rotor as the distance between the pad and the rotor get larger.

I've found that sometimes the pistons don't move in equally. It may be due to more friction in the piston seals, or just some other unknown reason.

So when you squeeze the lever, the pistons shift and maybe the left one moves in a little bit while the right piston moves in a little less and results in the rubbing.

It eventually settles down so that the pistons move in equally, but the center point will have shifted from the middle of the caliper.

What you can do is after you have gone through the "hold down the lever, tighten the caliper bolt", and the "squeeze the lever a few times and the pad rubs", is to note which side of the caliper the rotor is rubbing (drive/nondrive side), then loosen the caliper bolts just enough that you can physically shift the caliper so that the pads no longer rub. Then tighten down the caliper bolts alternately a quarter turn each. Basically, you are just re-centering the calipers physically rather than relying on squeezing the lever and tightening it down.

It helps to have a white sheet of paper underneath the calipers so you can determine which pad the rotor is rubbing against, and to make sure that there is equal space between the rotor and each pad.

With the Avid mechanicals, you would generally do this by turning the adjustment dial on the drive/nondrive side until you adjusted the pads so they don't touch the rotor. With the hydraulics, you are not physically adjusting the caliper until the pads don't touch the rotor.

Try this first, but if this doesn't help, I'm sure there are some other tricks that can be used.

[benb]

Oh one other thing you can do if you're centering a hydraulic caliper is take all your zip ties, etc.. off the frame to make sure the line is not putting tension on the caliper that pulls it out of alignment before you can snug it down. You need to be careful torquing the bolts as well to make sure you don't twist it out of alignment by tightening one bolt too much before the other.

I guess that Hayes tool probably eliminates the need for all these tricks if you leave the shims in while you torque the bolts.

[Vinci]

I have had some rubbing with my TRP Hylex's as well. I was able to adjust almost all of it out, but I still get a little every now and then. Thus far, I have attributed it to the hydraulics not opening the pads as wide as the mechanical calipers will, which would make them more tolerant of little errors in either disc true or caliper alignment.

[NHAero]

Thanks to all. Last night I got slightly better results in the workstand by changing to the brand new rotor that came with the Hylex. I can't detect any warping on the KCNC rotor that was on the wheel, but it certainly is lighter.

[NHAero]

Yesterday I had the good fortune to bring my bike to Mike Zanconato at his shop, as he offered earlier in this thread. Problem solved, in a three step process:
- first Mike trued up the front rotor - it was a new one but still out 0.008 by his dial indicator
- next he faced the adapter. On the front, where I hadn't been able to get any calipers to work except tha BB7s with the conical washers, he took off a fair bit of material. It was clear that alignment was a bit off, as initially all the material came off of one edge. He did the rear as well but it didn't need much.
- finally, he took a small amount of brake fluid out, as the pads weren't fully retracting. This final step did the trick - no more rubbing.

It was great to see his shop and work in progress , and get help from one of the nicest and most capable folks anyone could hope to meet. Thanks Mike!