Soft Brake pedal when starting 2016 2500

[Omadra15]

Any suggestions on teoubleshooting a soft brake pedal when I start up my ram 2500 6.4L? It only goes to the floor when I start it randomly isually after it sits a few days unused and only happens at slow speed when I back out or pull out of my driveway. If i pump the pedal a few times it regains firmness and no issues when driving at higher speeds above 15mph.
Not noticing and leaks in the cab or onnthe driveway

 

[Grams]

Sound like a normal “leak-down” rate of the vacuum booster. It recovers immediately after the engine starts… Right?

 

[04fxdwgi]

Sound like a normal “leak-down” rate of the vacuum booster. It recovers immediately after the engine starts… Right?

If it was the vacuum booster leak down, it would be a very hard pedal at start up.

Going to floor is a hydraulic problem, such as a MC or leaking caliper.

 

[Mojo88]

Brake pedal "goes to the floor" is a real warning sign that something's wrong. I agree with @04fxdwgi , this is a hydraulic issue. If no visible fluid loss and if fluid level is OK in M/C, I would suspect internal bypassing of M/C. If brake fluid level going down in the M/C, well, then you would need to find the leak somewhere in the system (which still could be the M/C, leaking out the back).

Get it fixed........

 

[Daw14]

This is serious,and should be properly diagnosed, and repaired before it goes to the floor unexpectedly.
Crawl under and look over all the brake lines for signs of fluid.
If you can’t find anything and it is not using fluid, I would suspect internal master cylinder issues.
Now that I’ve read the prior post again, what Mojo replied is very good advice and I recommend the same.

 

[Omadra15]

I read/watched on YouTube that it could be also due to a worn out wheel bearing. I know I have one in the front passenger side that is acting like it needs to be replaced. Could this be causing it?

 

[Daw14]

NO.

 

[04fxdwgi]

I would suggest that if you are posing these questions, perhaps it's better to have a more experienced mechanic do the work.

Braking system is nothing to experiment on.