Brake pedal hard to depress - DeVille Cadillac Cars & Trucks

Hi Ross.
Common reasons for this to happen:
Bad brake booster: The most common culprit of a hard brake pedal is the brake booster. A bad brake booster will be unable to provide vacuum assist, meaning that you will be attempting to depress the brake pedal with no assistance.
Vacuum Pressure. Vacuum - or really lack of vacuum pressure - is the most common cause of a hard brake pedal, and therefore the first thing to look at when a hard pedal is present. ... An improper amount of vacuum creates a scenario where the diaphragms can't move the pushrod into the master cylinder
Read up more at this link.

https://www.google.com/search?q=Hard+break+petal&rlz=1C1OKWM_enGB877GB878&oq=Hard+break+petal&aqs=chrome..69i57j0l7.438j0j7&sourceid=chrome&ie=UTF-8
or this one.
https://techtalk.mpbrakes.com/how-to-series/how-to-diagnosing-a-hard-brake-pedal

Most likely a failed master cylinder or vaccume leak to the booster. Here is how to check for a bad brake booster first with the vehicle off depress the brake pedal usually once or twice is sufficient but however long it takes to make the pedal as firm as possible now with your foot on the brake pedal pushing down start the car if the pedal moves your boosters not at fault it's your master cylinder or another problem if it doesn't move its most likely a booster problem

Are you brake lights coming one when you press the brake pedal? If not, the issue is probably a dead battery. If the lights are coming on, it is probably a defective brake switch (which tells the car when you are pressing the brake).

I need to know if the brake pedal gets tight or does the brakes get tight and slow vehicle down as if brakes are being applied.....If it is just the pedal getting tight and hard you have a vacuum Brake Power booster problem....If the brakes are locking slightly this could be a few different things......NEED MORE INFO..and Mileage....

Not sure if you have done all this.



BRAKE BOOSTER INSPECTION

Functional test:
1. With the engine stopped, Depress the brake pedal several times, then depress the pedal hard and hold that pressure for 15 seconds. If the pedal sinks, the master cylinder, brake line or a brake caliper is faulty
2. Start the engine with the pedal depressed. If the pedal sinks slightly, the vacuum booster is working. If the pedal height does not vary, the booster or the check valve is faulty

Leak Test:
1. Depress the brake pedal with the engine running then stop the engine. If the pedal height does not vary while depressed for 30 seconds, the vacuum booster is OK. If the pedal rises, the booster is faulty
2. With the engine stopped, depress the brake pedal several times using normal pressure. When the pedal is first depressed, it should be low. On consecutive applications, the pedal height should gradually rise. If the pedal position does not vary, check the booster check valve.

Check valve test:
1. Disconnect the brake booster vacuum hose at the booster.
2. Start the engine and let it idle. There should be a vacuum available. If no vacuum is available, the check valve is not working correctly. Replace the check valve and retest.

END TEST

1. Check the fluid level in the reservoir after bleeding each wheel. Add DOT3 fluid, if necessary.
2. If the master cylinder was disassembled or if the reservoir becomes empty, bleed the air from the master cylinder as follows:
   1. Disconnect the brake lines from the master cylinder.
   2. Slowly depress the brake pedal and hold it.
   3. Block off the outlet plug with your finger, and release the brake pedal.
   4. Repeat 3 or 4 times.
   
   
3. Bleed the brake starting with the one furthest from the reservoir and then the next furthest, etc.
   
4. Depress the brake pedal several times, then loosen the bleeder plug with the pedal held down.
5. At the point when fluid stops coming out, tighten the bleeder plug to 11 Nm (8 ft. lbs.), then release the brake pedal.
6. Repeat until all the air in the fluid has been bled out.
7. Repeat the procedure to bleed the air out of brake line for each wheel.
8. Check the fluid level and add DOT3 fluid if necessary.

It is most likely the alternator.

the brake switch may be failing, causing the gears to stay in a locked position making it hard to shift into park

Make sure the vacuum line running to the brake booster(round drum behind the master cylinder) is still in place. If so then you may have a failed brake booster which will make a hard pedal and hard to stop.

check under dash for a leaky vaccum switch. if booster was faulty brake pedal would be very hard to depress.