Frustrating front brake problem

[stoinkythepig]

My bike seems to warp rotors. I replaced them recently because they had warped (I measured runout). I just figured it was age, they were getting thin. The new ones stayed straight for a week or two and now they too are warped and seem to be getting worse. I tried new pads, no difference, the bearings seem smooth and free of excess play, the fork bushings seem OK, and the calipers operate normally without any signs of sticking.

The apparent (I have not measured them yet) warping shows up under moderate braking. If I brake really hard, they feel pretty smooth, but as I reduce lever pressure the bike shudders a bit.

I'm baffled, any ideas? I'm planning to replace the wheel bearings since I can't think of anything else that would cause this. They do have 91,000 miles on them.

[slammp]

I would say bearings too - only other thing I could think of is if you were running ceramic pads as those get a lot hotter than oem and could cause the warping.

[Expat]

Are the pistons sticking on the caliper? (damaged seals, excessive crud or corrosion would cause this) If they are, they may be rubbing on the rotor causing excessive heat which may lead to warping when you brake hard... Just a thought??

[R7]

If I brake really hard, they feel pretty smooth, but as I reduce lever pressure the bike shudders a bit.

Sounds to me like the calipers are slow to release and maybe sticking just a little bit. You probably wouldn't notice it in a spin test while the bike is on the stand, but add in the heat from braking and a ever so slight drag from the caliper, and you could be overheating the rotor. Just IMO of course

[stoinkythepig]

Sounds to me like the calipers are slow to release and maybe sticking just a little bit. You probably wouldn't notice it in a spin test while the bike is on the stand, but add in the heat from braking and a ever so slight drag from the caliper, and you could be overheating the rotor. Just IMO of course

Are the pistons sticking on the caliper? (damaged seals, excessive crud or corrosion would cause this) If they are, they may be rubbing on the rotor causing excessive heat which may lead to warping when you brake hard... Just a thought??

They release cleanly and immediately when I release the brake lever. I've taken them off and exercised all six pistons in each, they seem fine. The shudder I was trying to describe is when I am still applying moderate pressure to the brake lever. Thanks for the thoughts though, if the bearings don't sort it out, I'm going to buy some used calipers for it.

[stoinkythepig]

I would say bearings too - only other thing I could think of is if you were running ceramic pads as those get a lot hotter than oem and could cause the warping.

I have always run OEM style pads. Thanks though.

[tonup]

Did you ever find the cause of your warping?

[stoinkythepig]

Did you ever find the cause of your warping?

Nope, can't find anything wrong, other than the warping. I did change the front wheel bearings (which seemed fine) and straighten the rotors (one was out by 15 thousandths), but the problem came back I've learned to live with it by using the rear brake more and trailing off with the front for the last 20 feet of stopping under normal conditions. The warping is hardly noticeable under hard braking. Might rebuild the calipers over the Winter, even though they seem to operate perfectly.

[Jim]

Caliper rebuild takes less than an hour. I wouldn't wait until the winter

[Paul_E_D]

I don't think it's actually warping. If you can't feel it at high speeds then it's not really a "problem".

I can't remember what you have tried, but it could be as little as contamination on rotors or pads. Start with a fresh set of pads, clean the rotor really well with brake clean, then sand lightly with 300 grit paper, spray again, assemble with gloves on, and bed it the new pads.

Or, remove the spring washers from your rotor buttons. Sometimes those are so tight that they actually put the disc out of spec ever so slightly...

[Stromper]

Really examine the floating bushings. One sticking can cause strangeness

Additionally loosen axle
Retighten everything with the brakes on hard a coupler of wacks with a soft faced hammer to help thing move and line up. The axle pinch bolts.

Additionally use a file and/or fine sand paper or emery to dress/polish where the pads move against the metal supports

[DuncanMoto]

Buttons sticking.

[stoinkythepig]

I don't think it's actually warping. If you can't feel it at high speeds then it's not really a "problem".

I measured with a dial indicator, they are indeed warped.

[stoinkythepig]

Buttons sticking.

I spun all of them many times. None were stuck.

[stoinkythepig]

Really examine the floating bushings. One sticking can cause strangeness

Additionally loosen axle
Retighten everything with the brakes on hard a coupler of wacks with a soft faced hammer to help thing move and line up. The axle pinch bolts.

I did all of the above already.

Additionally use a file and/or fine sand paper or emery to dress/polish where the pads move against the metal supports

That's one I have not tried yet. Thanks.