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

When you say you left it open and pumped the brakes. Does that mean you left the bleeder open and pumped the brakes? If so, you were pulling air back in. You need to hold the pedal break it loose and then tighten it, then pump them up.

Here is a video that is kind of what we are talking about:

https://youtu.be/szmeEX9haS4

Okay. We need to narrow this down. So let's cap the master cylinder ports so that we can eliminate everything except the master cylinder. Then confirm the pedal is hard. The only thing I can think is there is a line(s) that is failed that is expanding when you press the pedal which is allowing the pedal to go to the floor.

However, if the pedal still goes to the floor with the master cylinder then we know it is that. If it is not, just add one line back on at a time so we can find what leg of the system is the issue.

I understand. However, we need to start narrowing down the system because with all this info we are close to making an assumption based on past parts replaced. This assumption that something is fine because it has been replaced is going to potentially cause us to chase our tail.

I would suggest to cap it off for two reasons. First it will confirm what we suspect which is it is okay. Second it will completely isolate the system allowing us to add one leg of the system back in one at a time to see when the pedal starts dropping again. Clearly each leg that you add back on that has no issue the pedal will stay hard. Then once it drops we know where to go.

Yes. Sorry. You just need bolts that will fit in the master cylinder which will cap it off. Just make sure they are the same depth of the line "nuts" that come out of the master cylinder.

And yes. By legs I mean the lines going to each wheel.

This is possible but I have never had to do that. I attached the process and is worth a try.

Understood. Sounds good. We will wait to hear back. Thanks for the update.

Yeah. Unfortunately that is the next step. The fact that the pedal is hard with the truck off and goes to the floor shows the booster is working. Basically the booster is just there to assist you in pushing the pedal. It makes it easier.

Clearly we have fluid escaping from somewhere. Either past the master cylinder or an external leak which we have proven out. If you cap off that master cylinder and it still goes to the floor then we know that is the issue. If it does not go to the floor then add the lines back on the master cylinder one at a time to find when it goes to the floor again.

Thanks. Keep us updated. Have a great July 4th (assuming you are in the USA).

Thanks. Love FL. Will be visiting the pan handle in Sept. We will wait to hear back. Thanks

You could do that but I would take the lines off the master cylinder so that it eliminates everything except the master cylinder. Then as you put the lines back on one at a time, you can find where the issue is. Keep us posted. Thanks