Intermittent brake pedal going to the floor

Hi,

It sounds like the master cylinder (MC) is bad. What happens is the plungers in the MC wear and allow fluid to bypass them. As a result, the pedal will slowly go to the floor. Most times you are able to pump them back up and have them work, but the problem will happen again.

Take a look through this link:

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

If you were to bring the truck to me with these symptoms, this would be the first suspect. If you decide to replace the MC, here is a link that shows in general how it is done.

https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder

Here are directions specific to your vehicle. The attached pics correlate with the directions. Note that it is important to bench bleed the new MC prior to install or connection.

Caution: Refer to Brake Fluid Irritant Caution in Service Precautions.

Notice: Refer to Brake Fluid Effects on Paint and Electrical Components Notice in Service Precautions.

1. Apply the park brake and block the wheels.
2. Disconnect the electrical connector from the brake fluid level sensor.

pic 1

3. Disconnect the brake pipes from the master cylinder.

4. Important: Install a rubber cap or plug to the exposed brake pipe fitting ends in order to prevent brake fluid loss and contamination.

Plug the open brake pipe ends.

5. Remove the master cylinder mounting nuts.
6. Remove the master cylinder from the vehicle.
7. Remove the master cylinder reservoir.

Installation Procedure
1. Install the master cylinder reservoir.
2. Bench bleed the master cylinder. Refer to Master Cylinder Bench Bleeding .
3. Important: If the seal is missing or damaged, replace the seal. Be sure that the O-ring is seated against the master cylinder base, not in the groove.

Install the O-ring seal to the master cylinder.
4. Install the master cylinder to the vehicle.
5. Notice: Refer to Fastener Notice .

Install the master cylinder mounting nuts.
Tighten the nuts to 36 Nm (27 ft. lbs.).
6. Remove the rubber cap or plug from the exposed brake pipe fitting ends.
7. Connect the brake pipes.
Tighten the fittings to 25 Nm (18 ft. lbs.).
8. Connect the electrical connector to the brake fluid level sensor.
9. Bleed the hydraulic brake system.
10. Release the park brake and unblock the wheels.

Check out the diagrams (Below). Please let us know what happens.

Hi,

I really think you are not getting all the air out of the brake system, Don't read to much into the ABS brake system for this can be done without a scan tool, You need to bleed from the source in this case will be the Master Cylinder, you can bleed the calipers until you wear out the bleeders and you still will not have a good brake pedal. Have a helper and start at the rear line on the master cylinder one pump hold the pedal down than crack the nut open let all the air out tighten the nut and let pedal up, (Waiting 10 to 15 seconds between pedal pumps, Start vehicle in between bleeds but do not push the pedal now shut down and start again (Do not rush this you will end up with bad results), Bleed the rear line of the master cylinder until you do not see any air bubbles coming from the line nut fitting, Do the same process to the front line of the Master cylinder, ( Keep checking the reservoir fluid level do not run the reservoir dry or you will need to start all over again), Once the Master Cylinder is bleed start bleeding the wheels, Starting at the right rear wheel it is farthest away from the master cylinder, Do the same process pump the pedal one time hold down and open the bleeder let the air out and tighten the bleeder and let the pedal up, Wait 10 to 15 seconds between pedal pump until all the air is gone at the bleeder, (Take your time wait for the fluid to fill all the reservoirs in the braking system before each pump), Next do the left rear, right front and the left front, (Do not dwell on the brake pedal height in the shop bay),
Check the braking on the road test for braking power. (NOTE if your brake pedal fades out at stop signs replace the master cylinder repeat bleeding procedure).
(Make sure all brakes are adjusted to specs). Please let us know if this bleeding procedure was helpful and if you need any more information.

Thank you
Joe Terwilliger