I recently acquired a 2007 Ram 1500 4.7L truck. The brake pedal is 'spongy' (almost to the floor) on the first pump but I get a firm and solid brake pedal with accompanying stopping power on subsequent pumps.
I've bled all four corners and checked the vacuum hoses for leaks. There are no weeping or outright leaks in the master cylinder to (4) disk brake calipers.The master cylinder visually appears to be in good shape but I haven't torn it apart yet.
The rear brakes use a disk brake for stopping power and a drum brake for the parking brake. My wandering mind is starting to think that this may be the problem area.
Before I rip out and replace everything from pedal to all four tires, I'd like to ask if I'm missing something a little less obvious.
fwiw, this is a 4.7L 6 speed manual