The brakes have always been trouble-free, they automatically "set" themselves, but something's up now. Yesterday, after driving down the freeway for 5 miles, I found that the front brakes were dragging. (And no, I wasn't riding the brake pedal.) On the off-ramp, they slowly brought me to a stop without touching the pedal. Needless to say, they were HOT. I had an IR guage with me, the left rotor was off the scale (over 525F). The right one was ~ 500F. (The rears were at ~ 150.)

I haven't done anything to the brakes lately, haven't been on the track in a couple weeks. I run the Cobalt GT Sports and leave them on all the time. All else related to brakes is stock.

After letting it sit for five minutes, the drag was gone. I drove home slowly and later pulled the pads, and everything appears fine. Rotors are true. Plenty of wear left on the pads. When I tried to depress the big plunger, however, I couldn't budge it. A clue?

Any help would be appreciated.

Stuart

 

Very weird. First thing I'd do is to bleed the whole system. Fluid that might have an air pocket might play havoc with the system. Check all lines for signs of leakage. Do you know if the ABS if fully functional? You can test it by using the brakes hard on a slippery surface like sand, gravel, leaves or wet.

 

Do you track the car? I experienced a similar problem in the car that I used for HPDE events. It was caused by the deterioration of the piston dust seal and having the particles jamming themselves in between the piston adn its bore. It wasn't so much that the brakes were self-applying, but that they did not release properly once applied. A caliper rebuild using new seals and boots solved the problem.

 

I had the same experience as CoralDoc. A rebuild solved my problems, too.

 

If a petroluem product finds it's way in the brake system, it will cause the seals in all the calipers/modulator/master cylinder to swell and deteriorate. You'd be surprised how many oil change places have added oil to the brake reservoir.

The brake calipers will not release with contaminated fluid.

Unfortunately, the repair is to replace every hydraulic component in the brake system.

 

Check your pbrake edal position. You may find that the brake light switch may be pushing on the pedal slightly, or the pushrod may need adjusting. Aftermarket cruise control pedal switches may do the same as well.

As soon as the master cylinder is pushed the vent drillings to the reservoir get blocked and fluid cannot find its way back from the wheel cylinders as it expands. One test it to put the car on full lock and loosen a bleed nipple just enough to leak a tiny amount of fluid while the brakes are hot and dragging. If the brakes stop dragging its a residual pressure problem rather the binding pistons. Generally, if both front are effected its more likely to be a residual pressure problem.

Good luck

Chris.

 

Great feedback. Thanks much. I guess a caliper rebuild is in my future (and yes, I track the car ~8x per year).

 

when you say you tried to depress the plunger and it wouldnt budge, were you talking about the piston?

I used to have one rotor significantly hotter than the other, and experienced brake drag, as well as vibration at speed after the brakes got hot. Then when tried to replace my pads the piston wouldnt depress easily at all (compared to the other side).

I took apart the caliper for a rebuild and guess what i found. The dust boot was not seated properly, there was significant crud in under the boot.

AND worst of all there was rust on the piston (its steel i dont know how) the rust on the piston had changed the surface hieght by a 1-2 millimeters ( a huge amount, for something that should be smooth).

So since i didnt have a new piston on hand i cleaned everything off put in new seals/boot and reassembled. I left it like that for about a week (worked fine, but wouldnt reccomend) till i got the new piston and did the whole process over again.


I suspect that prevoius owner didnt bleed the brakes at regular intervals, and this is what caused the problem, the fluid was murky black, but now everything is clean and clear and under control.

 

btw some tips for rebuilding calipers:

1. cover everything in the general area with painters plastic sheeting ( fender etc)
2. To get the piston out slide caliper up, stick some wood in there and have someone lightly depress the brake (with hand or feathery foot), as the piston comes out stick a smaller piece of wood or somthing and press the brakes again. Or you could use compressed air once the caliper has been removed. Be very very very carefull when you do this, it only takes single digit psi to get the piston to come out with significant force. DO NOT under any circumstance have your fingers in the path of the piston when it may move.
3. When you disconnect the banjo bolt from the brake lines to caliper, wrap a pen or somthing in plastic and stick it in the hole on the brake line to prevent excessive leakage, which may lead to empty resevoir
4. Feel free to use all the cuss words you know when you are trying to get the dust boot/piston reassembled. But here is what i did. First install the seal, 2nd install the dust boot without the piston or grease. Then use either hemostats or a friend to hold the dust boot wide open while you insert the piston into the caliper. Then with the piston almost all the way in but not enough the the dust boot will fall into its groove, cut the corner of the grease and wedge it under the boot, then squeeze out the grease while rotating the packet around the outer edge of the piston. Greasing at the end allows you a better grip on the boot while you try to stick the piston in.

There will be three greases, two sealing washers, 2 caliper pin boots, a piston seal and a piston dust boot in the rebuild kit.

1.The orange grease goes on the caliper slide pins on the metal on metal sliding part.
2. The clear grease goes inside the caliper pin boots. and other rubber stuff which doesnt get too hot like brake lines.
3. The red grease goes inside the piston dust boot.

I may be forgetting some stuff.

 

Hey, tizbad, thanks for all the good info. Yes, I was talking about the piston. My rubber seals tore some time ago. Someone on the forum said don't worry about it, cause the heat from tracking will just do it again. So I didn't. I guess it's time to pay the piper now.

I'm still concerned about Chris' caution about the master cylinder being out of position, since the problem occurred on both sides simultaneously. Guess I should check that first, but I expect the pistons will still need some work.

btw, how do you protect the new seal from the heat -- just alum foil?