Freefallman

I am able to true my rear disc brake so there is clearance from the pads while working in my apartment. However, when I get to where I ride I find that it's rubbing and squealing. It's pretty hot right now. What's going on here? Do I have air in my line that is expanding in the heat? Is my wheel flexing under my weight? Is it possible that the rotor is changing shape slightly in the heat. This is driving me nuts so any help would be appreciated.

SlowCrank

How is the bike positioned when you are truing? In a stand, upside down, on a kick stand? Are you truing the rotor, or just trying to get wheel placement correct?

What worked best for me (assuming your rotor and wheel are true and your hub is packed correctly) was to flip the bike upside down, leave the wheel loose in the dropout then adjust the calipers until they are as close as possible. Then squeeze the brake, and with the brake tightened, lock the wheel in place. This hopefully centers the rotor between the calipers.

There were also times (with crappier brakes) that I would just have to hold the wheel in place so that it wasn't rubbing then tighten the bolts.

Lastly, I upgraded to Avid BB7s. I could never, never, never get Novella Tektros to stay true or not to squeal. And yes, the rotor (and wheel) will shift a little when under weight, so you may also just want to loosen up on the tolerance of the brake pad positioning.

fietsbob

If in Doubt, bleed it out.

Freefallman

I'll bleed it. Damn. I wanted to avoid doing that.


Slow Crank:
It's been in a stand face up. I know the trick about braking before tightening the calipers. No dice. Guess I'll just play with it some more. Thanks for the advice.

Kimmo

That the clearance disappears indicates expansion in your line. Ergo, there's gas in it.

Also, do folks toe-in disc pads? I'd try it.

SlowCrank

I don't think it's possible... ?? All the pads I've seen have been held in place magnetically. Though I've only used mechanical and not hydraulic.

Kimmo

I don't see why you couldn't stick a little shim on the back... 0.5mm should do it.

FBinNY 

If it's heat related, then you need to bleed out an air bubble. But if you're looking to avoid that here's a quick diagnostic to rule air bubbles in or out.

Put your bike in the sun for a while, and see if it's the sun or that you're riding that's the problem. If it's the sun, the brakes will rub without weight on the bike, but if it doesn't than something is moving under load.

The most likely load related cause is sloppy wheel bearings, axle play, or possibly frame deflection (but not likely disc warpage). You can confirm this by seeing if you have problems riding where the sun isn't heating the lines. Find a place to ride it indoors, or during the cooler evening, and see if you have problems or not.

Either way, your first step should be to try to isolate the issue as heat or weight related, then move from there.

If it isn

SlowCrank

Honestly, this seems dangerous. YMMV.

And per FBinNY, I've also heard it can be incorrectly packed wheel hubs.