When I push pedal; once in a while brake pedal

double check the brake master cylinder and brake piston cylinder.

hissing sound is a vacuum leak somewhere on the power assist part of the system as in a bad booster..try this test..with the car off..push the brake pedal down a few times and release all the vacumm and see how far the pedal goes down..after a few pumps with your foot it should become hard and drop just a bit..once it feels"solid' or hard..hold the pedal down with moderate pressure.. and start the car back up..the pedal should drop a bit further but less than halfway.. if it drops further it needs attention..good luck especially if it goes almost to the floor..

Do you mean the pedal goes to the floor, or you push the pedal and the car does not stop ?

Clutch plate and pressure plate seem to be too weak to pull the car. To test the clutch plate, park the car on flat surface. Pull the hand brake up, start the car, depress the foot brake pedal, depress the clutch pedal, put the car in 1st gear, press the gas pedal and leave the clutch pedal at once, while keeping the brake pedal depressed.
Follow one of the two following statements:
1. Engine does not shut down and remain start. (Clutch plate, pressure plate and clutch bearing defective - Replace all as a set)
2. Engine shuts down. (Clutch system is OK and does not require any repair).

replace calipers and bleed the system

Should be on brake pedal under dash, could be brake switch is sticking or bad try pulling up on your brake pedal, if tail lights go off that's what it is, if not your switch is staying stuck in.

Most brake light switches ratchet into position and self-adjust. To reset the adjustment, press the brake pedal part way down & pull the switch out toward the pedal until it clicks several times.
Hope this helps.

Did you adjust the brake light switch correctly? To adjust the brake light switch, first press the brake pedal down a few inches, then pull the switch plunger rod out of the switch toward the brake pedal arm, as far as you can without using excessive force. Next, return the brake pedal to the pedal stop position against the pedal stop and pull the brake pedal toward the rear to push the brake light switch actuating plunger rod into the switch housing limited by the travel of the brake pedal arm rear travel stop position. This procedure automatically adjusts the brake light switch correctly.
If the brake lights still don't turn off with the brake pedal released, check the brake pedal arm for sticking or binding that is preventing the brake pedal arm from returning fully to the pedal stop when the brake is released.

It probably indicates that the cable is not being fully retracted when brake is disengaged. Spray as much of cable as possible with WD-40, allow to sit for a few hours, the engage and disengage the brake several times untill it loosens. If this fails the cable may be stretched and needs to be replaced.

Two persons are required: one to bleed and other to press brake pedal.
Remove wheel and hub of the side you want to bleed. You will find the bleed nut there. Open it a little until some oil flows out. Ask the other person to press brake pedal with steady pushing and withdrawing until he feels its tight while you slowly tighten the nut. Adjust tightness of pedal by trial. Don't forge to refill the brake fluid after bleeding all the brakes.

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