Brake pedal very hard to push - 1999 Cadillac DeVille

No vacuum to the power brake booster.

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.

_______power brake booster, check vacuum to booster and the check valve for brake booster. primary symtom is high hard pedal that requires greater then normal pedal pressure to stop car. testing booster= pump brakes several times with engine off to deplete stored vacuum. turn on engine with pushing slightly on brake pedal. you should be able to feel the pedal fade away a bit, and then become firm. But not hard. if you feel nothing at the pedal when engine starts. Brake booster is not working. Good-day! make sure vacuum is going to booster with engine running. it may just be a bad vacuum line or check valve.

I had this same problem (brake lights won't come on when pushing on brake) I found that the brake light sending unit had come out of adjustment.Look under the dash by the brake pedal.There is a plastic threaded unit that needs to be pushed back towards the brake pedal lever.Careful not to push it to far or the brake lights will stay on. Hope this helps

the brake booster will make the brake pedal hard to push. they get that way usualy when they loose there vacume. if you dont hear a vacume leak with engine running then i would start with replacing the booster

EITHER YOU STILL HAVE AIR IN BRAKE SYSTEM OR YOU HAVE FAULTY BRAKE MASTERCYLINDER.IF BRAKE PEDAL WAS GOING TO THE FLOOR FIRST OF ALL AND BRAKE FLUID WAS NOT LOW.MOST LIKELY BRAKE MASTERCYLINDER IS FAILING.

need to replace the power brake booster. the vacuum diaphragm in the booster has bursted causing the noiseand the hard brake pedal.

not sue u have abs on that model
more than likely break booster
best way to check booster is stop truck pump pedal a few time then put your foot on brake pedal and push down this is with truck stopped ,keeping pedal pushed start engine brake pedal should move down more if booster is working check all pipes tp booster

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.

Yes it could be the booster.