brakes started at floor first time you applied them

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.

the guide help me fix it thank you.

My brakes are going to the floor and truck is barely stopping. I replaced the master cylinder, bench bled it first then installed it. Bled all the lines working from the furthest ( rear passenger) to the front. Made sure clear fluid came out with no air, pedal was firm until I started it. Then it went to the floor again. I cracked open the ABS actuator lines and bled them ( in lines first the exit lines ).. What AM I DOING WRONG?? How do I bleed the ABS.? Please help.

You only need to bleed the system at the wheels. Try that again and if necessary start the engine while bleeding.

Does pumping the pedal a few times with engine started makes any difference to the pedal height?

I did all you suggested, once engine is started it goes to the floor, pumping brakes has little or no difference, I think the ABS actuator has air in it. I need a way to open the valves to properly bleed them. any Ideas?

Sorry for the delay.

If pumping the pedal does not make any differences, you are correct about the ABS accumulator being the culprit but it is not air in the system that is causing this. In fact it is due to lack of back pressure.

One way of doing it is to get a scan tool to perform bleeding of the ABS system.

Try this, drive vehicle on a sandy patch and press the pedal hard to jam the brakes. The accumulator should work, keep repeating until the pedal becomes firm.

I had changed my brake pads about four or five months ago and when I did my piston literally fell out and I believe it was because the c-clamp I used got stuck in the hole of the piston. I then put it back together but noticed a small leak. Well I didn't repair it at the time but was never a big issue. About every other week I had to refill brake fluid. As time went on I had to refill more frequently. So about a month ago my brakes started getting worse until they finally just quit. I decided to bleed them. That back brakes were fine but not the front, pedal goes to floor and won't pump up. Traced it all the way to port on the master, not getting any brake fluid out of the one port for my front brakes. Did a bench bleed and both ports worked fine, put back on my truck and had same issue. I then called everyone and nobody knew so I went and got a used one, put it on and got great brakes. Well, here it is about a month later and now I'm having the same issue again, pedal to the floor. Yesterday I bought a rebuild kit with seals only but still the same problem. Why?

Good morning,

Did you replace the caliper that came apart? If you did not, replace that caliper.

As far as the master, installing used brake parts is never a good idea. The seals internally in the master failed. They do sell the rebuild kits but they never work. The bores are aluminum and they pit internally and will not hold pressure anymore.

You need to get a rebuilt master cylinder.

Roy

Well it's just strange how my original master cylinder and the used one I purchased done the exact same thing. Speaking of the caliper, I replaced the seals.

Again, using used parts in the brake system is never recommended. I would use a rebuilt cylinder only.

Hopefully, the caliper is not pulling air into the system causing a bad pedal as well. I would replace that as well with a rebuilt caliper.

Roy

Okay, I attached the procedure for replacing the master cylinder. This needs to be either new or rebuilt. I attached the part below.

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

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

I also attached the procedure for the calipers. You never said anything about replacing the leaking caliper after your repair.

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

https://www.2carpros.com/articles/brake-caliper-replacement

Roy