I have a '97 F250 diesel with about 180K. The brake pedal is very hard to push. I have replaced the power brake booster there is vacuum in the hose going to booster (i started truck took hose off booster and felt the vacuum in the hose). What else coulod it be?

The most obvious cause for a hard pedal is simply not enough vacuum. Check the brake power booster by pumping on the brake pedal while the car isn't running. Continue pumping until you've "bled off" the vacuum from the booster. Hold the pedal down while you start the car. The pedal should go down a bit more beneath your foot. If it doesn't, then you should examine the connection between the vacuum hose of the brake power and the engine's vacuum.
Replace the brake power booster if the connection's fine, which would fix the hard brake pedal problem.

It may be your calipers need replaced. Check them for signs of wear. Look at the metal spring where the brake pads sit.
Apply tension to the pad and see whether you hear a pop. If you do, the brake pad is moving too much on the bracket. Replace the caliper. This could help the hard brake pedal.

NO. the vacuum is used to make the brake pedal easy to push, power brakes. the pedal would be hard without vacuum, that is why the pedal gets hard with the key off and engine not running. the problem you are having is more of a hydraulic problem.
Have the brakes checked asap. the brake system may have a leak causing the pedal to go low. check the fluid level and if it is low or empty then there is a problem, could be a rotted brake line leaking or a wheel cylinder leaking.

You may have lost you brake assist. Look for any disconnected or broken hoses and vacuum leaks especially the one going to the brake booster. make sure that the check valve is good it should allow air through in one direction but not the other. if all checks out good apply vacuum to the power brake booster and make sure it hold if not replace the power brake booster.

Your power brake booster is controlled ny vacuum so if it was going bad or if you had a leak in the vacuum hose that connects to your brake pedal would be hard. I hope this helps and good luck.

Toyota93 man,
I have the same problem with my 97 f-250 right now, same engine. I just replaced the booster and it didn't solve the problem. Obviously we are losing the vacuum somewhere. Check your vacuum lines for cracks as that is the cheapest. also the check valve on the booster itself. The vacuum line from the booster goes to a "vacuum tree" "vacuum solenoid"? I dont know, no one can tell me. Not even the ford dealership. but its mounted on top of the wheel well and it has 4 vacuum hoses coming off of it. The largest hose then goes to a vacuum pump on top of the power steering pump. That is my next change. I'll let you know if that fixes it. Let me know if you get an answer.
mike

It appears that you have lost the vacuum assistance that works the power booster for the brakes. It is most likely that the vacuum hose that connects from the vacuum pump (which is usually located on the rear of the alternator) to the power booster has gone hard and split where the hose attaches to the metal piping. Check the hose for leaks or splits and re-terminate or replace as necessary. If the hose is OK then the problem could be that the vacuum pump is faulty or the rubber diapraghm inside the power booster has become faulty and developed a leak. A brake specialist would be the best option to sort out these latter problems.

the problem is caused by either a failed power brake booster vacuum diaphram or a loss of vacuum to the booster, most likely the booster is defective, if this is a diesel then check the enginge driven vacuum pump.

They need to be bleed again all four wheels but your vacuum pump may be bad since diesels don't have vacuum then have to have a pump, check that the booster one way check valve is good if you can blow thew it both ways it's bad, to bleed start from the wheel farthest away from the master cylinder pump the brakes 5 times and hold down then open the bleed valve keep doing this until you get clear fluid out of each wheel once you have done that if it is still mushy and you know you have vacuum re bleed with engine running this will help push more out with power assist. most like the hard brake pedal had to do with no vacuum check out the pump. You may also have to reset the 2 way check valve if you need help with this let me know.

When you press on the brake? Have your brake vacuum assist checked. It,s that bigspaceship looking thing between the brake master cylinder an firewall. good luck and be safe.

Check front calipers, caliper should "float" to be self centering. If the caliper is stuck only the inside pad is pushing on the rotor instead of the caliper pinching the rotor. You will need to remove the caliper from the assembly, there are usually rubber boots to keep out the dirt and water from the slide pins, they are ofter cracked/broken or missing altogether. You may need a small torch and some rustbuster to get things moving again.