When i'm driving, the brake pedal goes slowly to the floor on its own, applying the brakes, unless I hold the pedal up with my foot...is this a brake booster problem

your ebrake is on try pulling the handle and push it back down or get the foot pedal to release. if that's not it. you have to check the fluid level. or you have air in the system. does the pedal feel spongy when you stop on the brake pedal. if it slowly goes to the floor you could have another problem with air or a leak

Further information will be required unless you would nlike a simple solution like.
Step one start said vehichle
Step 2 apply foot ti brake pedal and put gear selector in drive
Step 3 remove foot from brake pedal to accelerator pedal
Step 4 apply presure to accelerator pedal untill desired speed has been acheived
Note these steps will not work for manual transmission see section 37

For braking see section 22

You have a leaking brake line or Caliper. You need to fix the hole by replacing parts.

Hi, you have air in the brake pipes and lack of fluid. Your car needs to have the brake fluid topped up and all the brakes bled to get the air out of the system. Until this is done your car is unsafe and should not be driven. If you drive it in this condition you are liable to kill somebody, especially if a pedestrian steps off the kerb in front of you. Get your car sorted out and get it sorted out quickly and don't drive it on public roads (unless driving very slowly to the garage) until it is fixed.

Hissing sound indicates booster diaphragm has torn. Please let me know if you would like instructions for replacing the booster.

There is never a test or reason to pump your brakes

Accomplishes absolutely nothing.

There is no pressure in a braking system at all,
until you SLOWLY apply the brake pedal.

Then less than 1" off movement in the master cyl,
will develop 600 to 1800 lbs at the wheels

Release the brake pedal, the system goes to zero,
IT DOES NOT HOLD ANY PRESSURE

To answer your question

You not suppost to press the pedal hard
The saying goes--you apply the brakes,
not force the pedal arm and pin into the
vacuum booster, as though you want to damage it

When your driving what happens ?
You have higher manifold vacuum and
thus your pedal is normal,why the VACUUM
brake booster

try this ABS bleeding procedure:

WITHOUT TECH 1® OR T-100®

Do not place your foot on the brake pedal through this entire procedure unless specifically instructed to do so.
This method can only be used if the ABS warning lamp is not illuminated and not DTC's are present.

1. Remove your foot from the brake pedal.
2. Start the engine and allow it to run for at least 10 seconds while observing the ABS warning lamp.
3. If the ABS warning lamp turned ON and stayed ON after about 10 seconds, the bleeding procedure must be stopped and a Tech 1® must be used to diagnose the ABS function.
4. If the ABS warning lamp turned ON for about 3 seconds, then turned OFF and stayed OFF, turn the ignition OFF .
5. Repeat Steps 1-4 one more time.
6. The entire brake system should now be bled by following the guide or pressure bleeding procedure.

Manual Bleeding
See Figure 3

1. Clean the master cylinder fluid reservoir cover and surrounding area, then remove the cover.
2. Add fluid, if necessary to obtain a proper fluid level, then put the reservoir cover back on.
3. Prime the ABS hydraulic modulator/master cylinder assembly as follows:
   1. Attach a bleeder hose to the rearward bleeder valve, then submerge the opposite hose end in a clean container partially filled with clean brake fluid.
   2. Slowly open the rearward bleeder valve.
   3. Depress and hold the brake pedal until the fluid begins to flow.
   4. Close the valve, then release the brake pedal.
   5. Repeat Steps 3b-3d until no air bubbles are present.
   6. Relocate the bleeder hose to the forward hydraulic modulator bleeder valve, then repeat Steps 3a-3e.
   
   
4. Once the fluid is seen to flow from both modulator bleeder valves, the ABS modulator/master cylinder assembly is sufficiently full of fluid. However, it may not be completely purged of air. At this point, move to the wheel brakes and bleed them. This ensures that the lowest points in the system are completely free of air and then the assembly can purged of any remaining air.

Fig. Fig. 3: ABS hydraulic modulator/master cylinder bleeder locations

1. Remove the fluid reservoir cover. Fill to the correct level, if necessary, then fasten the cover.
2. Raise and safely support the vehicle.
3. Proceed, as outlined in the following steps, to bleed the wheel brakes in the following sequence: right rear, left rear, right front, then left front.
   1. Attach a clear plastic bleeder hose to the bleeder valve at the wheel, then submerge the opposite hose end in a clean container partially filled with clean brake fluid.
   2. Open the bleeder valve.
   3. Have an assistant slowly depress the brake pedal.
   4. Close the valve and slowly release the release the brake pedal.
   5. Wait 5 seconds.
   6. Repeat Steps 7a-7e until the brake pedal feels firm at half travel and no air bubbles are observed in the bleeder hose. To assist in freeing the entrapped air, tap lightly on the caliper or braking plate to dislodge any trapped air bubbles.
   
   
4. Repeat Step 7 for the remaining brakes in the sequence given earlier.
5. Carefully lower the vehicle.
6. Remove the reservoir cover, then fill to the correct level with brake fluid and replace the cap.
7. Bleed the ABS hydraulic modulator/master cylinder assembly as follows:
   1. Attach a clear plastic bleeder hose to the rearward bleeder valve on the modulator, then submerge the opposite hose end in a clean container partially filled with clean brake fluid.
   2. Have an assistant depress the brake pedal with moderate force.
   3. Slowly open the rearward bleeder valve and allow the fluid to flow.
   4. Close the valve, then release the brake pedal.
   5. Wait 5 seconds.
   6. Repeat Steps 11a-11e until no air bubbles are present.
   7. Relocate the bleeder hose to the forward hydraulic modulator bleeder valve, then repeat Steps 11a-11f.
   
   
8. Carefully lower the vehicle, then check the brake fluid and add if necessary. Don't forget to put the reservoir cap back on.
9. With the ignition turned to the RUN position, apply the brake pedal with moderate force and hold it. Note the pedal travel and feel. If the pedal feels firm and constant and the pedal travel is not excessive, start the engine. With the engine running, recheck the pedal travel. If it's still firm and constant and pedal travel is not excessive, road test the vehicle and make sure the brakes are operating properly.
10. If the pedal feels soft or has excessive travel either initially or after the engine is started, the following procedure may be used:
    1. With the Tech 1® scan tool, Release then Apply each motor 2-3 times and cycle each solenoid 5-10 times. When finished, be sure to Apply the front and rear motors to ensure the pistons are in the upmost position. DO NOT DRIVE THE VEHICLE.
    2. If a Tech 1® scan tool is not available, remove your foot from the brake pedal, start the engine and allow it run for at least 10 seconds to initialize the ABS. DO NOT DRIVE THE VEHICLE. After 10 seconds, turn the ignition OFF . The initialization procedure most be repeated 5 times to ensure any trapped air has been dislodged.
    3. Repeat the bleeding procedure, starting with Step 1.
    
    
11. Road test the vehicle, and make sure the brakes are operating properly.

perhaps the master cylinder is sick put a little pressure on the pedal and keep your foot on the pedal just to keep it hard a little if the pedal goes down slowly the it s the master

you either have air in the brake lines, a cracked brake line, or low of brake fluid... either way you will need to bleed the brakes

have you had the brake pads changed recently?

Most of the time this will be a worn out master cylinder bypassing fluid inside its self.or sending fluid into the brake booster