The power brake booster is failing.
Hardness in the brake pedal can because by low brake fluid. Air in the brake lines can also cause the pedal to push hard.
The brake pedal vibrates.
Any time the brake pedal is hard to press then you need to check and see if the brake booster is functioning properly.
A hard brake pedal can be caused by several different factors. It can be as simple as the brake pedal getting caught on something to the power brake booster being bad. You could also have a brake pad or shoe that is sticking, causing the brake fluid to boil. When brake fluid boils, it expands and can cause the hard brake pedal that you feel. A brake pedal that is hard to press can also be caused by a build-up of water in the brake line. The water in the brake line lowers the boiling point of the brake fluid. A hard brake pedal can also be the result of a restriction in the brake line, such as a bent brake line or foreign material in the brake fluid. The most common cause of a hard brake pedal is the sticking brake pad or shoe, causing the brake fluid to boil. Tracking down what is causing the hard brake pedal can be frustrating, to say the least. Take the vehicle for a drive and when you come back, feel your brake lines near the wheels. Caution: The line may be very hot! If one is extremely hot, you may have just found the culprit causing the hard brake pedal.
Adjust or replace the stoplight switch at the upper end of the brake pedal under dash area
Get some speed up, then brake hard. If you feel the brake pedal pulsating you have ABS:
Usually when a brake pedal feels more stiff than usual, there is a vacuum leak. The brake lines probably should be bled.
more than likely you have air in brake line and need to bleed brakes
Yes, you will feel the brake pulsate. Just keep full steady pressure on the pedal and steer around the accident if possible.
With the engine off, press hard on the brake pedal. Turn the engine on and the pedal should depress slightly but no more than an inch or two. If your brakes either drag or stick on, or sometimes the pedal goes real hard under foot it means your servo is shot!
if the brake pedal is hard you might first want to check if the mineral oil is full, get the castrol mineral oil for jaguars with the attached pump. Make sure the oil level is green with a black dot, if is clear with a black dot then the container is empty and it needs oil.,, Good luck bud..!!
Probably the brake booster going bad.