Hard brake pedal on cadillac

If you follow that wire around you'll find the relay and fuse under the pump motor if I remember correctly however the hard pedal is almost always caused by a failed vacuum booster or the vacuum line between the engine intake and the booster, you don't have to disconnect the master cylinder brake lines to change the booster.

Booster problems are rare but they do go bad sometimes.
A bad booster generally causes the brake pedal to feel hard to push down, and a lot of pressure on the brake pedal is required to make the car stop.
Rarely, a vacuum brake booster will develop a vacuum leak, which can cause engine performance problems, hissing or whistling noise, as well as requiring increased pressure on the brake pedal to stop.

The first test:
With the vehicle parked, turned OFF, and the parking brake set, pump the brake pedal 5 to 6 times. If the pedal gets harder to push after several times, your booster is probably good.

The second test (To make sure):
After the test above, without making any changes, press and hold the brake pedal with light to moderate pressure.
Now with your foot still on the brake pedal, start the vehicle.
If the booster is good, you will feel the pedal go down when the engine starts.

Hope this helps!

_______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.

Pretty normal to not be able to lock the brakes without the assistance of the booster, it'll take a lot of pedal pressure without it. It's also normal for the pedal to feel harder without the booster, this goes for any car/truck with power brakes. Try it with any other car you have and you'll see.

I've worked on several old Cadis but don't recall what year they started using front disc. If it's been changed from drum to disc you'll likely need a different proportioning valve and possibly a different master to get them to work right. Talk to the seller and ask if the brake feel changed when they replaced the master and if they changed any other parts.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/oscar_403cc49e0f00cda7

Fig. 31: Vacuum circuits - 1984 V8 4.1L engine Fed. and High Alt. (DFI)

Fig. 33: Vacuum circuits - 1984 V8 4.1L engine Calif. (DFI)

Hope helps. Just keep in mind that your feedback is important and I'll appreciate your time and consideration if you leave some testimonial comment. Have a nice weekend and thanks for using FixYa.

Jose.

well, a hard firm pedal, usually indicates a bad brake booster or a vacuum leak to booster or the vacuum check valve, on booster. TO TEST BRAKE BOOSTER; pump brakes several times with engine off to deplete stored vacuum. turn on engine with pushing slightly on pedal. you should feel the pedal fade away a bit and then become firm, but not hard. if you feel nothing at the pedal when engine starts the booster is at fault. good-luck !!

i would start by checking the brake vacuum booster, the booster is what make the pedal power brakes and easy to push, also take a look at the master cylinder for leaks at the rear of it as the fluid leaks out the rear it goes into booster and destroys the rubber diaphram.

the hose between the inlet manifold and the vacuum canister is leaking/clip gone,or the vacuum canister has gone.....check visually for cracks/air leaks(best if someone in car pressing pedal with your head under hood....

After you changed the calipers did you pump the brake pedal til it came back up to normal?If not you have to do this to get the pistons back up against the pads.The pedal should come back up.Also did you bleed the brakes after you reinstalled the calipers.This also has to be done first.I should have mentioned this first before pumping the pedal.Sorry.So bleed the brakes first.

What model car? On my Cadillac the problem was the vacuum line to the release valve at the parking brake pedal. The problem can be the vacuum line, the release valve or the vacuum actuator for that release valve. Mine was on the steering column.