brake locking up while Im driving

[ace1500]

I have a 07 (newer body) 1500 silverado 4x4 and the problem ive been having is my front brakes starts to lock up while im driving and my truck starts to shake (even more then I brake) I also noticed my trans temp always gets above 150 when this starts to happen. When the trans temp gets in the 171s I have to stop and pull over because the front brakes are completly locked and usually smoking if I dont pull over soon enough. I dont know what would be causing it now. Ive replaced the brake booster and master cyl. the last thing ive noticed is that even when I come out to my truck in the morning the trans temp wont be the outside temp it would usally be 10 degress or more above outside temp. Please help! im at a dead end!

[Jsdirt]

Sounds like your calipers are junk. Been a GM staple from the '96 model year onward - if they sit parked any length of time, the pistons extend normally when you hit the brakes, but never retract ... and the hotter they get, the tighter they clamp. GM seems to be using substandard seals & pistons in these things. Can't tell you how many sticking brakes I've fixed over the past 8 years ... Luckily my '07 hasn't been one of them, but it's been garaged since day one every night, and these days most of the day too, unless I have a car or truck to deliver.

 

I wouldn't worry about the trans temp too much. Your still in the safe zone there. If it stayed north of 200° for a long time, then I might be concerned.

 

Just yesterday I delivered a '85 K20 diesel with a 8' plow in the bed - had to weigh over 5k lbs. easy. There was a section of road that climbed a 9% grade for a few miles, ambient was about 60° - the trans hit 210° . On the other side of the mountain, it dropped 30°. I run 100% Amsoil in the trans, so that was well within the safe zone. I've seen Amsoil tests with 300° fluid! Only way a tranny is hitting that temp is if it's slipping with a big load onboard on a hot day.

[sahls01gmc]

I had the same problem with my truck. Mine happened to be the master cylinder. Sounds like yours is the front calipers. I would replace the lines from the calipers to the hard lines as well since you may have a collapsed line.

 

171 is nothing, that's still in the safe zone.

[Doug_Scott]

First thing to do is as soon as the brakes are locked on, open the bleeder screw on the caliper and see if brake fluid squirts out. Tighten bleeder screw and see if brakes are still locked up. If opening bleeder screw did nothing, the calipers are likely in need of a rebuild. If opening bleeder released the brakes, then you have an issue somewhere between the brake pedal and the caliper.

Common causes are flex lines that are breaking down inside, creating small flaps that act like a one way valve, caliper sliders starting to seize up, compensating port blocked or plugged in master cylinder. This can happen if the push rod between master and brake booster is too long.