When engine on pedal sinks to floor with minimal braking power

This sounds like the ABS module is having a problem, I would have a shop with a tech2 open the valves and have the system power bled, this should remove the air in the system.

When you set the pads did you push down and let up slowly? if not the system is full of air due to the small orifice in the master cylinder.

Here is a guide and video on how to do it correctly:

https://www.2carpros.com/articles/how-to-replace-front-brake-pads-and-rotors-fwd

And how to bleed the system:

https://www.2carpros.com/articles/how-to-bleed-or-flush-a-car-brake-system

Let us know how it goes so it will help others.

Best, Ken

One of three possibilities here. The first is that there is an air bubble in the system somewhere. You would fix that by doing the standard brake bleed procedure on each wheel. See this article: https://www.2carpros.com/articles/how-to-bleed-or-flush-a-car-brake-system

Start with the wheel closest to the master cylinder (Front driver wheel), then do the next closest (Front Passenger), then the next (rear driver) and then the rear passenger.

The other possibility that I can think of is a bad brake master cylinder. If a master cylinder fails, it can result in brakes that unpredictably spongy. Sometimes they will be normal, other times (usually when you are approaching the busiest intersection in town at a high speed and the light turns red) they will halfway or completely fail.

I would bet on the first possibility. And since it is a nearly free fix, it is much more convenient.

There is a small possibility that your ABS module (if your truck has ABS) is acting up, but you would probably see the ABS and Brake light on your dashboard.

Try bleeding ABS unit manually before bleeding brakes normally. If this does not work find someone who has a tech 1 tool with the appropriate cartridge to do it. Your best bet is to rent a power bleeder to do this and it will take a ton of fluid. Do with ignition off. See pictures instructions are on second picture.

Does it have an ABS unit? Did you bleed it after the M/C and in sequence

Here is a guide that can help you get the problem fixed.

https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

Please let us know what happens.

Best, Ken

Good to hear, please use 2CarPros anytime we are here to help.

Cheers, Ken

Good morning.

Do you have ABS? If you do there is a bleeding procedure you must follow.

Pressure Bleeding:

Note: The pressure bleeding equipment must be of the diaphragm type. It must have a rubber diaphragm between the air supply and the brake fluid to prevent air; moisture, oil, and other contaminants from entering the hydraulic system. Also adapters are needed. Depending on the type of master cylinder used.

Tools Required:
J-29567 Brake Bleeder Adapter (Plastic Reservoir)
J-35856 Combination Valve Depressor

Note: It is very important that the correct master cylinder bleeder adapter be used to avoid possible damage to the master cylinder reservoir.

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1. Fill the pressure tank at least 1/3 full of brake fluid. The bleeder must be re-bled each time fluid is added.
A. Charge the bleeder to 140 - 170 kPa (20 to 25 psi).
2. Use J-35856 to depress and hold the valve stem on the combination valve during the bleeding operation.

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a. Install the bleeder adapter so the leg with the release valve is towards the cowl.
3. Bleed each wheel in the following sequence.
A. Right rear
b. Left rear
c. Right front
d. Left front
4. Connect the hose from the bleeder to the adapter at the master cylinder.
A. Open the tank valve.
5. Attach a hose to a brake bleeder screw.
A. Immerse the opposite end of the hose into a container partially filled with clean brake fluid.
6. Open the bleeder screw at least 3/4 of a turn and allow the fluid to flow until no air is seen in the fluid.
A. Close the bleeder screw.
7. Repeat step six at all the wheels.
8. Open the bleeder screw on the Isolation/Dump Valve (vehicles with power brakes only).
A. Allow the fluid to flow until no air is seen in the fluid.
B. Close the bleeder screw.
9. Check the brake pedal for "sponginess", repeat the entire bleeding procedure if this condition is found.
10. Remove J-35856.
A. Disconnect the line from the bleeder adapter.
B. Remove bleeder adapter.
11. Fill the master cylinder to the proper level with brake fluid.

I have seen where the brake booster valve fails causing the brake pedal to go to the floor when the engine is running. So you are on the right track.

This guide can help as well

https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

Here are some guides to help you.

Check out the diagrams (Below)

Please let us know what happens.

Cheers

Good evening,

Sounds like you have air in the system. You need to pressure bleed the system. The vacuum method and the 2 person method is not enough to get the air out with the length of the truck.

You can rent one at a parts store. It will force fluid into the master cylinder and when you open the bleeders, it will force the air through the system and out the bleeders.

Roy