Past two days now, my brake pedal has been much firmer when applying brakes, but won't return upwards when released...to the point where I don't have to hold the pedal to stay stopped. What are the possible causes of this? Calipers were just rebuilt, so I'm guessing its something along the lines of a problem with the booster or mc.

Any help appreciated. Please don't tell me to search; I'm at work using my iPhone without wifi...too slow to look at every thread.

Thanks.

Since you just rebuilt the calipers, I'd suspect a problem there. Maybe one of the pistons is not in the cylinder correctly and not returning. Or maybe the caliper isn't sliding. DOesn't sound like a leak, though.

I'm getting a range of answers from several people, but thanks for your input. Guess I'll have to make a stop at the dealership.

Well, if you've even done a brake pad/rotor job, then you have enough experience to take them apart yourself and at least inspect them. The calipers come off pretty easily, especially with the myriad of DIYs on this forum and across the internet.

Have you checked you master cylinder's fluid level?

If the dealer did the work, then I would expect them to make it right. I think that is a good plan.

Have you checked you master cylinder's fluid level?
+1 on master cyl.

permit stated that the brake pedal stays down "..where I don't have to hold the pedal to stay stopped." I take this to mean that the bakes stay engaged without pressure on the pedal.

Why would low brake fluid cause that?

Yes, the brakes stay engaged without pressure on my part.

Fluid is fine, right where it always is.

Unfortunately, I got the calipers rebuilt from an independent shop back in California, and I'm in Arizona. It feels like all the brakes are being applied when this happens, so I don't think the blame is on a caliper. Has to be MC...maybe booster.

If you have DSC try turning it off and see if there is a change in the response. I think I read somewhere you can't drain all the fluid out without re-programming the braking system. Driving the car with binding brakes is rough on every moving part, trans, brake rotors, pads, bearings overheating...on and on

If the brakes are being applied while the car is moving, that wheel will get very hot. You might check the wheels after driving it a bit. If you find one is hot, you might want to remove that wheel and check the caliper and pads.

BTW, I've never heard or read about a master cylinder or vacuum booster failing this way, but that doesn't mean it couldn't happen. Usually the booster fails because the diaphragm leaks and it does not operate. The common failure for a master cylinder is fluid leaking by the seals which results in low brake pressure. It is entirely possible for the caliper piston to be "cocked" in the cylinder or the seals dragging in the cylinder causing the piston to bind.

Jim Knight makes a good point about the DSC. The issue is the ABS controller. As I understand it, you need a dealer type computer system to operate the ABS controller when you bleed the system if you let the fluid drain out of the ABS controller. That might be the problem.

Anyway, it's a good idea to have someone look at it. Brakes are important.

Sweet, thanks for more input. The brakes aren't coming on when the car is moving (on their own, that is), only when I apply them (problem is they stay applied when I'm done with them). So I'm not heating up anything more than I would during normal use, it's just annoying to lift the pedal up with the top of my foot every time I start moving again.

I'll try the DSC tomorrow morning on my way to work. Would be nice if that's a temporary fix before I have it looked at on Monday.

Turning off DSC did nothing.

If you can pull the pedal up with your tippy toe it almost sounds like a broken return spring somewhere, possibly in the master cylinder. At any rate what ever was worked on just before this happened is generally the culprit.

I think the return spring is actually on the brake pedal assembly.

I'll try to find this said return spring when I have the chance. I can bring up the pedal with my toes, nothing too forceful.

Calipers were done back in December, so I've taken those out of the equation. I just really don't think they're the reason.

Also, I'm not sure if this is coincidence of related, but I've noticed the pedal only stays down when the car is moving, overwise it slowly returns. Could be nothing, could be something.

T'was the brake booster.......or at least that's what the shop is replacing.