Had a problem going down road, brakes applied all by them selves, their was no give in break pedal, had to pull over, turned off, let sit for a half hour or so while trying to figure out what was going on, didn't find anything except hot hubs, started back up everything is good again, suspect the cruise control. I was messing with it earlier in the drive, about 20 min before it happen, pressed a few buttons, it does not work, anyone know how to test. I know don't press any more buttons, LOL!

 

Welcome to the forums.

First off, the cruise has NO affect on braking. None. Period. The only thing that makes the brakes function is the brake pedal.

Are you sure it was brakes?

Truck a stick or automatic?

 

Yes it was the brakes, felt rims around lugs , they where hot, brake dust was all over front rims, just washed day before. Brake pedal was very firm , would not move. Later, I found a hose coming from cruise servo with plunger, at top of my brake pedal arm. Does this apply the brakes. It isn't normally touching anything, their is a slight gap from brake arm.

 

That is a dump valve for the vacuum operated cruise servo. It dumps the stored vacuum in the system when you press the brake pedal.

 

^^Exactly.

I suppose it was both front brakes? It didn't pull to one side? They held the truck stationary after stopped? Then released after they cooled down?

I would do a very careful inspection of master cylinder, lines and calipers. Something is not right.

 

Yes it was both front brakes. Master and booster have both been replace about a month ago, fluid flushed out all bleeders until clean emerged haven't had any problems until now, maybe defective part.

 

Was the actuating rod at the new booster adjusted? If it's just a hair too long, it can cause this.

 

Make sure you have some free play in the pedal. The brakes should not come on right at the top.

 

Remove the Master cylinder and checked Booster push rod, way to long, 1.35, adjusted in to 1.0, any longer and I would have to draw in master cylinder to mate surfaces. 1.0 seams to be the perfect length to wear the Master cylinder mates up with Booster with no effort, pedal and brakes are fine now, problem fixed. Thanks for advice!

 

Glad it was that easy. I guess that even a new booster needs that dimension checked.