04 express 3500 6.0 v8 brakes lock up after driving 1 block pedal is very stiff and no movement crack lines loose at m/c and everything is normal vehicle has jl4 stability control can i usee a regular m/c on it and unhook stability control thanks for any help you have

 

Kind of interesting that there are no responses.

If the brake pedal is rock solid with very little play, sounds like there is no vacuum assist from the brake booster.

I had a vehicle where the car would stop but then the brakes would lock up. I checked and replaced just about everything such as pads, shoes, calipers, brake cylinders, master cylinder, proportioning valve, rotors and drums but it still kept locking up the rear brakes. I decided to change the booster even though it was a newer rebuilt one (about three years old) and upon disconnecting the brake pedal from the booster rod, the rod just fell out of the booster! After installing a "brand new" booster, the lock up problem was cured.

Good luck.

 

The "awaiting email confirmation" held me off. I can't even guess his issue since the grammar is so bad.
And there is no vacuum assist. Its hydro boost run off the power steering pump.
If he comes back, maybe he can clarify things.