Peek the Geek

I've been using these brakes on my '04 Marin Pine Mountain for a few years now, and no matter what I try, I can't keep the pads from rubbing on the rotors.

I've tried re-centering the calipers using Hayes' recommendation of loosening the bolts, squeezing the brake lever and re-tightening the bolts (several times). I've tried pushing the cylinders back in with a box wrench (several times). I've replaced the pads.

I've even had the mech at my LBS take a stab at it a couple of times. The first time he said he couldn't get rid of the rub and that "all disc brakes rub like that." The second time he got the wheel to spin freely, but on my first ride the rubbing reoccurred.

Today, I finally let my assistant see what he could do...



Unfortunately, he couldn't come up with a solution either.

Anybody got any advice or suggestions I may not have tried yet?

Wordbiker

Hayes brakes, while very reliable and simple...are not very tolerant of spacing or alignment issues.

Just recently I addressed an issue with a client's Hayes brakes, and the problem appeared to be a crash signifigant enough to bend not only the mounting adapter, but the disc mounting tabs on the fork itself. The solution was a mere shim, but it brings up the approach to disc brakes which is in essence:

A) Make sure the caliper is even capable of being centered. On several bikes I've had in recently, the caliper was mis-spaced from the initial setup. I had to shim the caliper with washers to put it into the range that the caliper adjustments would even be effective. The rotor should be sitting right in the middle of the gap the caliper body provides for it to pass through, disregarding pad adjustments. If not, shim it as close as possible, then do any pad adjustments.

B) Closing the caliper by squeezing the brake lever does not necessarily center the caliper. Sometimes you still have to manually "bump" the caliper to center it (or to adjust for rotation with calipers that allow rotation, such as Avids). With calipers that only have an inside pad adustment and single pistons I turn it in a few turns, grab the brake lever, set the caliper mounting screws, then back off the inside pad adjustment for clearance. If that doesn't do it, loosen the mounting bolts to "semi-snug" (just barely tight) then manually push the caliper into place, eyeballing the daylight between the pad and rotor as a guide, then snug the bolts.

C) For brakes with no rotational adjustment (such as Hayes) the only solution may be shimming the adapter or facing/truing of the rotor. Eyeball the gap between the brake pad adapter and rotor, then if possible, eyeball it from underneath, looking for an uneven gap, uneven spacing for top to bottom, or bent tabs on the fork. If not, shim until it's parallel and evenly spaced. If that's all good and parallel with the rotor, mount the caliper then check for centering, continue shimming as necessary.

D) The rotor may just be warped. You can always buy a new rotor, but if yours is warped, they can be trued and/or faced by a good bike shop. If that's not an available service, you can try bending it back to true using your caliper as a guide, grasping it with an adjustable wrench and tweaking it as necessary.

Peek the Geek

Thanks, Wordbiker, for the detailed response. I'm at least almost certain it is not a warped rotor, as the rotor seems fine, and the rubbing is consistent throughout the entire revolution. I've also tried "bumping" the caliper while squeezing the lever, also to no avail. And I know the fork tabs are not the problem, because this happened both on the original fork and on the brand new Fox I put on late last season.

I'll give the manual adjustment a go and take a closer look at the spacing, but it really seems there just isn't enough room between the pads. I did just replace the pads today. I don't suppose they need to be broken in to create more space, do they?

Thanks again.

Wordbiker

Hmmm...

You should have room even with brand new pads. It sounds to me like the pads just aren't retracting. Could mean you have a sticking piston and a rebuild would fix it. Have you tried bleeding the brakes?

I had a similar odd problem with another bike. I opened up the reservoir, pushed the pads in at the caliper and got rid of some excess fluid. It worked flawlessly after it was all together again. My guess is that the fluid had expanded and was pressurized due to a difference in elevation or temperature from where it had been shipped. The overfull condition wouldn't allow the pads to retract.

I hope that's some help.

P.S.: As for the statement, "All disc brakes rub like that"...errr, no. Any decent disc system can be tuned to not rub. The cheap ones are more of a challenge, nice brakes just make it easier (my favorites are Avid )

MudPie

I've had the Hayes HFX Nines for about four years, and shimming doesn't work in the direction for which I need to go. Someone once mentioned these brakes are "self adjusting". I'm not sure how it works, but here is what works for me.:

1. Remove pads
2. Walk pistons back into the calipers as far as you can
3. Replace pads
3. Insert a credit card (or a hotel room key card or one of those fake credit cards that arrive as junk mail...) between the rotor and pad. Sometimes, I have to coax the credit card into position.
4. Squeeze the brake levers with one good firm squeeze and release.
5. Remove the credit card
6. Check it out - hopefully it works.

I'm not sure why it works or how the "self adjusting" feature works. I'd like to study the hydraulic schematic, but it doesn't appear to be readily available. If anyone has one, please let me know.

Wordbiker

Here's the caliper rebuild manual. That may give some insight.

gwhunt23

I'll second MudPie's suggestion. If no great improvement, it wouldn't hurt to bleed the system. Although you probably don't have any air in the system, you push the pistons into their bores in the bleed process. This makes a difference when you seal the system again. Then use the credit card method as soon as you're done bleeding the system - don't squeeze the lever on a bare rotor at first.

If this doesn't help, you can call Hayes at 1-888-MTN-DISC.

Peek the Geek

Does it matter whether the card goes between the rotor and the inner pad or between the rotor and the outer pad?

MudPie

Yes, place the card where you want to increase the gap.

I think I also loosen the mounting bolts, place the card, squeeze the brake levers and tighten the caliper mounting bolts while I'm still squeezing the lever.

In my experience, once I do this, I am good until I replace pads in the future.

Stacey

Hydraulic brakes "self adjust" due to the stiction/deflection of the piston seal in the caliper bore.

As the brakes are applied, the piston seal which is contained in a grove cut in the brake piston ,sticks to the caliper bore a bit, even if it needs to travel to compensate for brake wear. When the brakes are released the flex of the seal will pull the piston and pad away from the disc a fraction

For a visual aid: Push a brush against the palm of your hand, see how the bristles flex and when you release pressure on the brush, the end of the bristles remain stationary and the brush retracts a bit? The piston seal does the same thing.

MudPie

Thanks for the explanation. It's much simpler than I thought and it makes sense - seems to be an artifact of the seal. (I thought it was a designed feature like some sort of hydraulic fluid by-pass groove).

Stacey

Glad to help.

Rev.Chuck

First I would try burping the mastercylinder as wordbiker mentioned. Sometimes there is just enough pressure in the reservoir to keep the pistons from returning properly

However, if the brakes have three years of good use on them, the square seals in the caliper are probably not gripping the piston and returning it. Once the seals wear out the piston slides thru them, when they are working right it is like Staceys haribrush analogy, the square seal(like an O-ring) rotates out of square when pressure is applied to the piston and then springs back pulling the piston with it when the brake is released. You can get piston/seal kits and fix this yourself. You need two kits to do one caliper and air pressure helps to get the pistons out of the bores. You also need a bleed kit.

Peek the Geek

Okay, I used the credit card trick and while there is still a bit of rubbing, it's much better than it was (for now---we'll see how permanent the fix is). I'm happy enough with the improvement that I'm not going to go into bleeds, burps, or replacing seals at this point.

Thanks for all the help, everyone.