So, I searched through the forums for a similiar problem. Didn't see one, doesn't mean I didn't miss it--so if this is an old tired problem just ignore me or point me at the archived posts.
Changed the brake pads on my '07 gxp three weeks ago. Did it like I always do, pressed the front pistons in with a c-clamp, pressed the rear pistons in with the tool I rented from autozone. Everything went relatively normal except for the amount of resistance I met pressing in the pistons, ended up having to open the bleeder to do so. (never ran into that before). After I was finished I set the pads, made sure the ABS was ABSing (gravel/sand driveway) and did a road test to verify even braking. MAJOR drag. Like, in an 1/8 mile it was a fight just to keep rolling. Opened the bleeder to let pressure off, let the rotors cool off, tried again. Same thing.
Fully flushed the brake system (two quarts of dot3, flushed til it ran clear). Very little changed. Changed the flex lines (all four)(all four wheels are affected, all four calipers are dragging, all four rotors are heating WAY up), things seemed better at first--still a little drag, but not like before, UNTIL I activated the ABS. Then I got lock-up again and had to open the bleeders front and rear to relieve the pressure.
So, drove around a little bit last night (12 miles), things seemed resolved. Wasn't building up much heat, didn't seem to have any drag. So I tried to drive to work this morning. ...had to pull over once in a 35 mile trip to open the bleeders. But, after that, everything was fairly normal. Except I noticed my brake lights are perpetually on.
I'm a helluva mechanic, but I'm not a car mechanic. I've never seen this. Anyone else?
welcome to the forum
Is the e-brake properly adjusted? Correct pads? (If they're thicker than they should be, they could be pressed against the rotor regardless of the pedal position.)
With the car in neutral and wheels off the ground, can you spin the wheels freely?
I didn't recall using a special tool for the rear brakes (I have upgraded calipers which are very different), but if the piston wasn't screwed in all the way, there could be a little too much pressure between the new pads and the rotor.
And, I just have to say this because I've personally seen it happen at an autocross tech inspection:
Did you put the pads in the right way? Friction surface against the rotor, rather than the backing plate on the pad?
The only things I can think of that would cause something like this on all four wheels is the wrong brake pads (too thick as raygun mentioned), the ABS unit, and a misbehaving pedal. I have to think that you would have noticed the pads being too thick, since you would have had to force them in, and doesn't seem likely. An ABS unit malfunction should (but may not) keep ABS from functioning and set a code and warning light.
The brake lights that you mention being always on are the brake lights on the back of the car, and not a brake warning light? If so, check that your pedal is returning all the way to the rest position. If it is binding or sticking on something the brakes would obviously stay on, as would the brake lights. As far as I know they are only controlled by the brake pedal position switch.
Your pistons are hanging up.
This happens like clockwork every time I change rear pads up here in the rust-belt to at least one side of the vehicle if not both, and sometimes the fronts depending on age, mileage and usage, though I can't say I've managed to have all four do it at the same time.
When you compress the pistons back into the calipers all sorts of rust and other garbage that used to be hanging out outside the seal underneath the dust boot is now inside or directly on top of the seal and the pistons don't retract when you let off the pedal. You can either buy new calipers ($$$$) or search for a rebuild kit (time and frustration.) If you go with the rebuild you'll need someway to make sure the seal surface of the pistons is nice and clean before re-install, remove too much and they'll leak, not enough and they'll stick again. Or keep driving and hope they continue to clear up.
P.S. If you didn't already, make sure all the slide pins slide and re-grease them.
Your pistons are hanging up........
So you think that his brake lights being on is a separate simultaneous problem, or a pre-existing one?
With multiple pistons stuck or sticking, it's very possible that the pedal is not returning enough to close the switch.
Or that's my theory anyway...
Quick test of this would be to pull up on the pedal, which should allow fluid in from the reservoir to support the pedal.
With multiple pistons stuck or sticking, it's very possible that the pedal is not returning enough to close the switch.......
Possible, but two things seem to make this less likely.
>The spring on the pedal itself should pull it back even if no fluid pressure is available to do it.
>He reported that he can open the bleeders and get the pistons to retract.
I FIGURED IT OUT. Only took three weeks.
About a year ago I had weirdo electrical problems, took it to the dealer--there was corrosion in and on the back of the fuse panel in the passenger side. (Caused fun things like the car thinking it was stolen and shutting off without much warning--something about odd resistance causing it to think the key wasn't in the ignition...) Anyway, they were able to repair it and I went on my way.
But. Apparently they did not properly latch the under-dash trim panel. Which was maintaining pressure against the brake pedal swing arm. Which was my whole problem. Everytime I bled the brakes, the panel slipped further down, resulting in brake-lock. But since I hadn't screwed with anything in that area, I didn't think to look until I noticed that the brake lights were always on...which is an electronic switch and has nothing to do with pressure in the brake lines.
Side note: the metal in brake pads is magnesium. Didn't know that. Very distinctive white sparks this morning.
K.I.S.S. rules again...thought I was going to have to change the abs module.