After parking my jeep Grand Cherokee 1997 for 3 years, I've decided to get it back up and running. My problem is that the brakes are not working. I can pump the pedal but then it looses pressure again. They were working slightly when I pressed the foot down to floor. Any ideas would be great! Could it be seized calipers, ect?
Check the master cylinder fluid level. If it is low or empty you have a leak. If the reservoir is full the likely cause is a bad master cylinder. To find the leak fill the master cylinder and pump the brake pedal several times. you should see it drip. depending on where the leak is you may have to crawl under the vehicle and look for a wet spot or stain.
As @mikes stated, you will need to inspect the brakes to see if they are leaking. A good way to do this is to change out the fluid in the system. By bleeding the brakes all the way around, you will be putting fresh fluid into the system and allowing it to work as good as it's going to at this point. Brake fluid should be changed every two years at a minimum, so it's something which is going to need to be done anyway. While you are at each wheel, you'll be in the perfect position to check the validity of each brake component. Look for leaks (obviously). You will also want to check the brake lines to see if there is any bulging. Another common issue is the rotors will have enough surface rust on them where the brakes won't be able to grab. If this is the case, you'll need to either replace these or have them resurfaced. Check the calipers for movement to ensure they are not frozen or stuck. Also, just because you don't find a leak doesn't mean the master cylinder isn't toast. If there were enough moisture in the brake fluid, it could cause corrosion of the seals in the master cylinder, which could allow it to leak down and lose pressure. This would be pretty hard to diagnose, other than what you've described already.