What's wrong if your brake is too stiff ? you can feel something wrong once you step on pedal slightly.

If your car has power brakes, a slight hissing noise when depressing the brake pedal is not unusual. However, if you are having issues with the brake pedal felling stiff or hard, then you may have a vacuum leak in the power brake booster. If that is the case, it must be replaced.

If its only when you press the brakes, there may be a vacuum loss in the power brake system. Check the hoses from the manifold to the master cylinder booster or the connection on the booster itself. The hose may be split or the connection loose and leaking air. The booster itself may have a ruptured diaphragm. To check this, start the engine and run for a few minutes. Press the brake pedal and hold in. Turn off the engine. You should feel the brake pedal drop slightly. Remove your foot off the pedal and press the brake pedal a few times. Each time you press it , the pedal should keep dropping slightly and feel harder and harder to press. This will let you know that the booster is working properly.

IS YOUR HAND BRAKE ON?IF NO, YOU HAVE A BRAKE PROBLEM.

yes but up to a point
the brake pedal should move about 1" to take up the pedal free play and then be applied smoothly as you press further
the harder you press the more solid stopping action you will get
that way you can feel the brakes working so that you can adjust the braking action for stopping
there should be no hissing noise that occurs when the brakes are being applied
you say hydro booster which is hydraulic booster but a hissing noise will come from an air leak in a vacuum brake booster which indicates that it needs repalcing

It sounds like a vac problem with the engine or the brake booster. The brakes should be vac assist and that vacuum comes from the engine.
If it were something with the ABS system you should have a warning light on the dash. Nothing in the transmission would affect the brakes.

With he engine running your pedal action is assisted greatly by the brake servo. The servo is a large diaphragm that is acted on by the suction delivered by a vacuum line from the the intake manifold. The fact that the pedal goes to the floor when the engine is running just shows how much assistance the engine suction provides to your foot pressure. It is obvious that you still have air in your system. I would suggest that you top up the master reservoir, start your engine and pump the brakes quickly until you feel some hard back pressure. This will ensure that the brake pistons have been fully extended. Starting with the most remote caliper (right rear) bleed off about half a pint of fluid. Ensure that no air is allowed to **** back in via the bleed nipple at any time. Refill the master reservoir. Next the left rear caliper, bleed off about a quarter of a pint. Refill reservoir. Bleed off a about quarter of pint from both front brakes. This should sort it out.

could possibly be vacuum assist check valve is defective and you are feeling the engine vacuum pulsations. Easy ck, Inexpensive, easy replace. Good luck. If you will, let me know. please

have the master cylinder checked

Try the following to confirm if is the servo unit .( engine off,pump few times the brake pedal to become stiff.Keeping pressed the pedal start the engine and if servo is working you will feel the pedal slightly goes down.If not will not move at all-remain stiff.) Also if you do have the check valve close to servo not working you can realize it by the engine idle ( erratic ) and the servo not working.The other possibility if the vehicle is fitted,the ABS unit itself.

if this bothers you enough to spend money trying to fix it. and there are no abs codes a tech can find. i would replace the rear wheel speed sensor. located on top of the rear axle.if it irraticly reads a different speed than the front wheels. your abs will give you a drop in pedal and grinding feel or a pulsating pedal. i hope this is helpful. your problem is not one most people can figure out at home. trust your tech understands your prob and wants it fixed also. dont forget he is trying to get paid.good luck