What would cause the brake pedal to be hard and not have any brakes on a 1983 Ford Trucks?

Answer 1

The most common is that you either have a vacumm leak or the brake power booster is failing internally. The way to check is: Run the truck and check for hissing noises under the dash (brake pedal area) and under the hood. If no leaks are heard then shut it off & don't touch the brake pedal. Beside the master cylinder there is a fat rubber hose going to the big round thing the master bolts to (power booster). The hose goes to a one way valve in the booster. With the vehicle off you should pull the valve out of the booster. It should be hard to pull out but it will come out with a hissing noise as the vacumm in the booster escapes. If it doesn't hiss then you may have a vacumm supply problem, check valve problem or the booster itself is leaking and the booster can't work without vacumm. With the hose disconnected start the truck & put your thumb over the end of the hose & see if there is vacumm coming from the engine to the booster. If no vacumm present loof for a supply issue. If it does hiss when you pull the valve then you need to undo the 2 bolts holding the master to the booster & pull it away from the booster CAREFULLY as not to damage the lines. Look at the rear seal of the master where it bolts to the booster to see if it's wet. If it's wet the brake fluid is leaking into the booster and has damaged the rubber inside. If no leaks are found it's also possible that the booster has failed due to age. At that point you will need to replace the booster and/or master.