disc caliper adjustment?

[nighthawk]

Setting up ekar on a bike for the first time. All good so far, but I’m struggling with the front disc brake caliper. The pads seem to insist on dragging no matter what I do. Have centered the calipers properly, multiple times. Have tried working the pistons in and out multiple times(pads out, light pressure on the lever to “compress” pistons, then pushing them back into the caliper with a tire lever). Have tried relieving pressure on the system with the bleed port out and working the pistons in/out, and soaking up the excess brake fluid from the bleed port. Have tried riding and braking hard to bed them in… still dragging.

What should I try next?

[Hilltopperny]

Try putting a piece of paper on each side of the rotor, loosen bolts on caliper, squeeze the lever and tighten the bolts, pull the paper from the rotor and see if it gives you a little extra room? I have seen this method recommended before for this type of scenario. Good luck!

Sent from my SM-S127DL using Tapatalk

[harblhat]

A last resort method I use is to do it by hand and eye, loosening one caliper bolt at a time and shifting the caliper by hand until I can see daylight on both sides of the rotor. It takes time and good vision, but it works.

If all fails, then the question is whether the caliper mounts are properly faced and the rotor is straight.

[Dave]

Checking rotor run out first is important. I made an extremely sensitive measuring tool from an old dial indicator I own and some aluminum angle. I attaches to the fork thru-bolt.

I try to keep the runout down to 0.002 inch or .05mm.

Feeler gauges can be used to check clearance or placed on one or both sides, between the pad and rotor, while tightening the clamp bolts. My calipers usually want to move too close to the left side of the rotor.

[vespasianus]

Also on EKAR.

First, make sure your mounts are properly faced.

Second, check the rotor to make sure it is not warped. Many rotors from all the manufacturers are often warped directly from the factory. I like the SRAM tool (cheap plastic) to bend them back.

Third, remove the pads and front wheel. When you pump the brakes lightly, do the pistons come out evenly and go back with the same level of force? If not, take them back to a campag retailer and have them warranty. When you do the above test, make sure you clean it all with alcohol and when you push pack, make sure you lube the piston with brake fluid using a cotton swab.

If everything looks good, look through the caliper to see what is rubbing and move the caliper accordingly. I have used a single sheet of thin paper on one side to push things out a bit. You can use a feeler gauge but keep in mind that many feeler gauges have thin coatings of oil on them to keep them from sticking to each other. If you use this on your pads and rotors, it will ruin them both.

Also, for the bolts, make sure you use some blue lock-tight to keep the bolts snug.

[John H.]

My guess is that the pistons are not retracted.
Here is what I do-
Get a SRAM brake spacer. One of the red things that goes in the brake when no wheel is installed. Get the one that clips to the pad bolt on one side and is open on the other side. These spacers have a fat side and a skinny side.
Start by removing your pads and use the pistons flat with a plastic tire lever. Then reinstall the pads. Put that spacer in with the fat side up, give the lever 5 hard squeezes where you hold it for a few seconds. Flip the spacer to the thinner side, give 3-4 lighter squeezes. Try to center caliper again if needed.
For me this sets piston distance 99% of the time.

[dddd]

Notice that the short length of hose from the fork leg to the caliper has to bend a good bit because of the location and angle at the caliper and at the hole in the fork where the cable disappears.
This bending applies force and torque to the caliper, pushing it to one side and tilting it on an axis relative to the plane of the disc.
Also note that the hose isn't perfectly straight to begin with, possibly adding to the bending force/torque needed to accommodate the path that is imposed on the hose.

It will take a degree of balancing force and torque to bias the caliper to be straight with the caliper's surfaces.

Adding a shim between the pad and rotor helps to achieve this alignment in theory, but in reality the disc will still flex (and twist) laterally to accommodate forces imposed by the hose.
It is typically only necessary to move the caliper laterally at it's two mounting points, since the mounting surfaces are assumed to be machined perpendicular to the disc (in the bad old days, or when working on an X-Mart bike, the mounting surfaces could be off, and there might even be swivel washers to allow the caliper to be adjusted/tilted parallel to a radially-disposed line along the surface of the disc).

So ultimately, I agree with harblhat that visual inspection of the gaps is needed, and which is best performed over a sun-lit floor surface or other white surface (as a background) to make the tiny pad-clearance gaps clearly visible.
It's also most helpful to observe any tiny bit of tilt or twist motion of the disc as the brake is applied and released, which can indicate which way that the caliper needs to be pushed and twisted. Observe the disc's lateral flexing both ahead of and behind the caliper! Keeping a bit of bolt tension on one mounting point while pushing the caliper to either side at the other mounting point is a good way to effect small changes at one mounting point while not disturbing good positioning at the other mounting point.

And, as John H. mentioned, one should be sure to start with a caliper that retracts it's pistons well clear of the disc's thickness when the disc isn't present.

[nighthawk]

Thanks for all the advice so far, definitely a few things to try now. I think John H is on the right path. The problem seems to be one of the pistons isn’t fully retracting. I tried moving it in (with tire lever) and out (with light pressure on the brake lever) several times to lube the seal. And after pistons are pressed in manually and pads are mounted, I can get good rotor alignment until I apply the brake, then the pad(s) are back to dragging. Going to try and work the pistons more to get them lubed better, and will try the cotton swab idea and engaging the brakes with a spacer in there.

Cheers!

[robt57]

I bought one of the tools. It slides in and spaces both sides of the rotor.

I used it with both sides together [rather than as meant] in between the pad and rotor more often than not.

Usually you can see a bias, bigger space and touch opposite side.

So on the touching side I've put both side of the tool, grab lever, and snug.

Don't over tighten, and grease the securing bolts and washers, not threads [unless campy sez to]. That last tightening seem to allow torque to move caliper often I've found. So slight tighten 2-3n force, and then tiny turns alternately if you got one that want to walk upon final snug. It probably does not need to be as tight as you'd think. Go with spec and have a torque tool is best.

I've had some just eye hand attention works best, and others an small adjustable wrench with a light rag fit to hold while doing the final snug.

Sometimes it enough to make you say, "I wanted discs, why?"

[Epicus07]

These are dirt cheap and work like a charm. https://www.universalcycles.com/shop...4aAtuuEALw_wcB

[MikeD]

What I found is that when I tighten the caliper fixing bolts, the adjustment moves. Very frustrating. My Hayes feeler gage is worthless on my one bike with Shimano brakes, so I've resorted to eyballing the gap to verify there is no rubbing. Very slightly bent rotors can cause a rubbing problem too, and should be dealt with first.

[vespasianus]

Originally Posted by nighthawk

Thanks for all the advice so far, definitely a few things to try now. I think John H is on the right path. The problem seems to be one of the pistons isn’t fully retracting. I tried moving it in (with tire lever) and out (with light pressure on the brake lever) several times to lube the seal. And after pistons are pressed in manually and pads are mounted, I can get good rotor alignment until I apply the brake, then the pad(s) are back to dragging. Going to try and work the pistons more to get them lubed better, and will try the cotton swab idea and engaging the brakes with a spacer in there.

Cheers!

If the pistons don't retract equally, or close to it, even if you set the system up without rubbing, it will eventually rub with use and time.

Get them warranted.

[culler763]

I use a q-tip with alcohol to clean the edges of the pistons - then set the travel with a piece of cardboard. Loosen the caliper bolts when insertinng the wheel and clamp the rotor before you tighten the caliper bolts. Rotation of the whell should assure that the travel is correct.

[dolface]

Park Tool has a good video on how to clean pistons: https://www.youtube.com/watch?v=vQXFFgRButo