I have the solution to your problem I have been thinking about it sir what is going on with you is you have air in your system and you did not properly bleed out your braking system that is why your pedal is touching the ground
SOURCE: hard brake pedal....booster tested and
The anti-lock brakes are tied into the front wheel bearings. If a wheel bearing is going bad, the computer may think the wheel is skidding which activates the a.b.s. I had the same issue on my truck. Different type of vehicle but same type of issue. Not a pleasant experience when you can't stop.
SOURCE: New master cylinder and still no pedal.
get a new mechanic. 66 charger is right about brake lines ,also wheel cylinders can leak air in but still hold fluid in same for calipers. also check proportioning valve. My ? is are you bleeding it out? You also need to bench bleed the master before installing it.
SOURCE: brake pedel pushes to the floor
pump the pedal about 10 times and see if it comes back up, u need to pump the caliper pistons out after a brake job.
SOURCE: I replaced my front pads ,master cylender,
IF, the brakes are set up correctly, and functioning correctly, you should be able to lightly press on the brake pedal, and WAIT for the truck to stop.
If you step hard on the brake pedal you'll be kissing the windshield!
The brake job on your truck was not done correctly.
1.Check the clearance of the brake shoes to brake drums. This has to be set correctly. They could be too far away from the drum.
Verify that the brake shoes were indeed replaced.
Inspect to insure that the rear axle seals are not leaking oil, and contaminating the brake shoes.
2.As answered, the flexible rubber to metal brake lines, should be checked.
The ones I'm referring to, is not only the flexible line that T's into the hard metal lines of the rear brakes, but all the other flexible brake lines too.
Specifically, the flexible brake lines from the frame mount to the disc brake calipers, and the flexible brake lines from the axle mount, to the rear brake wheel cylinders.
This is often an area overlooked by many mechanics, but should be checked at every time a brake job is done.
Most mechanics will do a cursory glance of the outside rubber sheath, but will not remove the lines, and inspect inside them.
The composition of the rubber sheath inside the flexible brake lines, is prone to breaking down. If your truck is indeed a 1990 model it is 19 years old, and way past time for these lines to be replaced. Only a thorough inspection will reveal whether replacement is needed.
The flexible brake line is composed of an outer rubber, (rubber like compound), sheath, a stainless steel braided inner core, and another rubber inner sheath inside.
This inner rubber sheath breaks down, and needs visual inspection, as well as the outer sheath.
The line is removed, and a bright light is used to examine the inner sheath, as well as the outer sheath. Bend the rubber part of the line, observe for minute cracking, ('Weather Checking'), inside and out. Observe whether the inner sheath is gummy, weather checked, or both.
When these lines break down, they will expand upon using the brakes. Just like a hard rubber balloon.
Result?
'Soft brakes'
When the inside rubber sheath breaks down, pieces of it can go through the brake line, and cause blockage of the brake fluid.
Result?
The brake mechanisms are not properly applied. (Caliper pistons do not exert enough force on the brake pads. Wheel cylinders do not exert enough force on the brake shoes)
Also, the inner rubber sheath can break down just enough, to form a small piece that acts like a valve. It looks like a small flap.
Result?
Brakes are applied, flap closes off fluid from going to the brake mechanisms. Pressure is released from the brake pedal, the flap opens out of the way.
Best bet is to replace all of these brake lines, if they are 19 years old, and have never been replaced.
That, is part of a true brake job.
Brake Power Booster:
There is a rubber diaphragm inside the drum shape. (Rubber like compound) This diaphragm can break down over time, and develop a pinhole in it. Listen for a hissing sound when the brakes are applied, for one. See if the brakes fade away.
Rubber vacuum line from intake manifold to Brake Power Booster. Check for hardening, and weather checking. This line hardens over time, and should be replaced. It is exposed to the elements that splash up, and the heat of the engine.
The rubber round seal of the brake power booster, where the vacuum line plugs into. This seal hardens over time, and weather checks. If it's in an unsatisfactory condition, there will be a vacuum leak.
Loss of brake power, or 'Soft Brakes'.
Brake Master Cylinder.
The Brake Master Cylinder develops moisture inside. This is caused by the metal casting heats up, then cools down. There is water, (Moisture), in the air, and when air is cooled down, the moisture is released.
After time, the moisture causes rust to develop at the bottom of the brake master cylinder's reservoirs. This rust contaminates the brake fluid.
(Resulting in less efficiency, lower boiling point, and less hydraulic action of the fluid)
The rust also goes through the reservoir ports, and blocks the fluid entrance of the brake mechanisms, causes corrosion of the brake caliper pistons, and caliper piston bores, as well as doing the same to the wheel cylinders.
This rust can also go into the mechanism of the brake master cylinder. Corrosion of the master cylinder piston, as well as causing the rubber piston cups to break down, or tear. Can also block the ports in the casting of the brake master cylinder.
It is for this reason that brake fluid should be flushed out, and Completely replaced at specified intervals.
When replacing brake pads, the bleeder valves should be opened, before the caliper piston is squeezed back into the caliper piston bore. If not, all the rust, moisture, and gunk is pushed up into the brake master cylinder.
[After opening the caliper bleeder valve, the valve should start leaking brake fluid out, or after the assistant slowly pushes down on the brake pedal. If not, the bleeder valve must be removed, and a device used to clean the orifice must be used. {Stiff wire. Sometimes requires a drill bit. Replacing is easier}
Again the same thing for the wheel cylinders.
Same procedure if the brake system is pressure bled]
SOURCE: replaced master cylinder, front brake calipers and rear calipers,
BY TRUCK HAVING ABS BRAKE.YOU NEED A SCANNER TO BLEED BRAKES THE SCANNER HAS TO RESET OPERATION OF THE BRAKE HYDRALIC SYTEM BEFORE YOU CAN BLEED SYSTEM.
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