Brake pedal it goes normal until close to the bottom and then continues about a quarter inch with a clunk at the bottom?

It sounds like they did not bench bleed the master here are two guides that will help us fix the problem

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

and

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

Please run down these guides and report back.

If there is no air in the brake system then the only two other things that can cause this problem is a defective master or the rear shoes are out of adjustment. Here are a couple of guides to help you get the problem fixed.

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

and

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

and

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

The clunk you feel is normal when the master cylinder bottoms out.

Please let us know what happens.

Cheers, Ken

Hello,

Does this truck have ABS? if so you will need to have the the ABS unit valves opened when bleeding using a scan tool.

This guide should help us:

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

Please run down this guide and report back.

The brake pedal should travel about 3 inches, you will need a scan tool to open the ABS control valves to get he air out, here is a guide that should help.

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

Please run down this guide and report back.

Hi,

Are there any leaks? Are the rear brakes properly adjusted? When you replaced the master cylinder, was everything bled properly.

Lets start by going through the following link. See if there is anything that helps. Also, let me know the procedure used when you bled the brake system.I would suspect there is air in the lines. These guides can help you fix it.

https://youtu.be/w7gUsj2us0U

and

https://youtu.be/WDxvEQrMkBg

and

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

Please run down these guides and report back.

Let me know.
Joe

Just to confirm. You mentioned the master cylinder was not bled to your knowledge. It must be if it was replaced.

Please confirm.

Joe

Good afternoon.

This sounds like you still have air in the system.

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

I posted the procedure below but the key is you need a scan tool that can perform the automated ABS bleed procedure. It sounds like you have in the lines and conventional bleeding will not work until you open the ABS valves. That is what the scan tool does to get rid of the air.

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

Roy

NOTE: This procedure only needs to be performed if the 4 wheel anti-lock brake (4WABS) hydraulic control unit (HCU) has been replaced.

NOTE: One conventional pressure bleed cycle consists of advancing the brake pedal to its extended position, opening the wheel cylinder bleeder screw, allowing fluid to be released into the waste container, closing the wheel cylinder bleeder screw and releasing the brake pedal to its full upright position.

NOTE: When any part of the hydraulic system has been disconnected for repair or replacement, air may get into the system arid cause spongy brake pedal action. This requires the bleeding of the hydraulic system after it has been properly connected. The hydraulic system can be bled manually or with pressure bleeding equipment Brake Bleeder.

NOTE: Performing the New Generation Star tester (NGS) program routine drives entrapped air from the otherwise inaccessible lower section of the 4WABS valve into the upper sections (accessible by bleeding the brakes). Subsequent bleedings remove the air from the system.

NOTE: Add recommended brake fluid as necessary throughout the procedure.

Wheel Cylinder Bleeder Screw
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1. Connect a clear waste line to the RH rear wheel cylinder bleeder screw and the other end in a container partially filled with recommended brake fluid.

2. With the RH rear wheel cylinder bleeder screw open, cycle the brake pedal until no more air is seen in the waste line.

Wheel Cylinder Bleeder Screws Torque Specifications
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3. Close the RH rear wheel cylinder bleeder screw and disconnect the waste line.

4. Repeat steps 1, 2, and 3 for the LH rear wheel cylinder bleeder screw, RH front disc brake caliper bleeder screw, and the LH front disc brake caliper breeder screw.

Connect Cable Adapter
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5. Connect the (A) NGS DCL cable adapter into the (B) vehicle data link connector (DLC).

Vehicle And Engine Selection
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6. Select VEHICLE AND ENGINE SELECTION and press trigger to start the NGS.

Select New Vehicle Year And Model
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7. Select SELECT NEW VEHICLE YEAR AND MODEL and press trigger to start the NGS.

Vehicle Year Selection
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8. Select the appropriate vehicle year application and press trigger to start the NGS.

Select New Vehicle Year And Model
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9. Scroll down to the appropriate vehicle application and highlight and trigger to start:the NGS.

Verify Vehicle Application
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10.The NGS will prompt you to verify correct application. Trigger the NGS if correct.

Select Diagnostic Data Link
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11.Select DIAGNOSTIC DATA LINK and press trigger to start the NGS.

Trigger Or Cancel Display
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12.Follow the NGS prompt PRESS TRIGGER TO CONTINUE or PRESS CANCEL TO BYPASS.

Select - Anti-Lock Brake Module
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13.Select ABS ANTI-LOCK BRAKE MODULE and press trigger to start the NGS.

Function Tests
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14.Select FUNCTION TESTS and press trigger to start the NGS.

Service Bleed Function
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15.Select SERVICE BLEED FUNCTION and press trigger to start the NGS.

Service Bleed Function
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16.Select PRESS TRIGGER TO BEGIN.

NOTE: The brake pedal should be depressed while this procedure is functioning. Perform at least five service bleed procedures.

17.Repeat conventional bleed procedure as outlined in steps 1 through 4.

18.If brake pedal feels spongy, repeat NGS service bleed procedure as outlined in steps 5 through 16 and repeat conventional bleed steps 1 through 4.

HI and thanks for using 2CarPros.

It sounds like an issue with one of the rubber brake hoses to the caliper. I need you to try this for me and let me know what happens.

First, safely lift the front wheels off the ground so you can turn them. Apply the brakes so the caliper locks. Open the bleeder on the brake caliper. Does the caliper release?

If so, do this. Apply the brakes to lock caliper. Release pressure at the master cylinder. If it doesn't release the caliper, replace the rubber brake hoses.

Here are the directions specific to your vehicle for brake hose replacement. The attached pictures correlate with these directions

Front brake hose
Removal:
Warning: brake fluid contains polyglycol ethers and polyglycols. Avoid contact with eyes. Wash hands thoroughly after handling. If brake fluid contacts eyes, flush eyes with running water for 15 minutes. Get medical attention if irritation persists. If taken internally, drink water and induce vomiting. Get medical attention immediately.

- Raise and support the vehicle.

Warning: the electrical power to the air suspension system must be shut off prior to hoisting, jacking or towing an air suspension vehicle, this can be accomplished by turning off the air suspension switch located in the right hand kick panel area. Failure to do so may result in unexpected inflation ()r deflation of the air springs which may result in shifting of the vehicle during these operations.
Disconnect Front Brake Hose
see picture 1

- Disconnect the front brake hose.
1 Remove the front brake hose bolt.
2 Remove and discard the copper washers. Plug the front brake hose.
3 Disconnect the front brake hose.

Remove Front Brake Hose
see picture 2

- Remove the front brake hose.
1 Disconnect the front brake tube fitting and plug the tube.
2 Remove the plug;
3 Remove the two brake hose frame bolts.
4 Remove the front brake hose.

INSTALLATION:

Front Brake Hose Torque Specifications
see picture 3
Front Brake Hose Torque Specifications
see picture 4

- To install, reverse the removal procedure.
Bleed the front brakes; refer to procedure in this section section.
Let me know what you find.

________________________________________________

Also, since both the booster and master cylinder were replaced, you really should check the push rod adjustment between the two. Here are the directions for adjustment, Pic 5 correlates with this process.

Remove the brake master cylinder: refer to the Master Cylinder, Brakes.

Power Brake Booster To Master Cylinder Push Rod Torque Specification

see picture 5

-Adjust the power brake booster to brake master cylinder push rod.
1 Measure the power brake booster to brake master cylinder push rod.
2 If necessary, adjust the screw to the proper length.

Let me know what you find or if you have other questions.

Take care,
Joe

Okay. Did you adjust the push rod? It sounds like something isn't put together correctly there. If nothing leaks, everything is new, either the master cylinder is bad or the push-rod is not properly adjusted and getting stuck causing the pressure to remain on the calipers. Try the release procedure I suggested. At least that way we will know if the problem is at the master cylinder or after it. THis guide can help us

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

Please run down this guide and report back.

Let me know what you find. I hope that takes care of it.

Take care,
Joe