Brake pedal knocks

Can you feel it in the pedal and I assume it did not do this prior to this repair? If not, then we need to suspect the master cylinder first and foremost because the push rod is the only non-hydraulic component that was replaced. The reason I think it needs to be a non-hydraulic component is because brake fluid moving will not cause a knocking noise. It is just fluid. So that means it needs to be an actual moving part.

Let us know this info and we can go from there. Thanks

No, it didn't knock before I replaced the master cylinder. I replaced the entire brake system because the truck has been sitting probably the last 15 years and the seals in the master cylinder were leaking. You could see the brake fluid on the brake booster.

Okay. Is there a feeling with the noise or can you only hear it? Can you feel a clunk in the pedal when it does it?

Yes, I can feel it too.

Okay. If you feel the knock then it is a mechanical component which is either the lever point on the pedal (doubtful as you didn't do anything to that) or the push rod in the master cylinder. Clearly we could be missing something but if it were me, I would return the master cylinder and have the warranty exchange it for you as that is the most likely cause. Clearly you need to bench bleed the new one and then bleed the rest of the system again.

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

Thank you I'll try that. And let you know how that turns out.

Sounds great. Let us know. We will wait to hear back. Thanks for the update.