dodge caravan brakes

i have a 1999 dodge grand caravan se 2wd. loss braking power. i replaced front brake calipers and master cylinder even though there were no visible leaks. still problems. when i start motor, brake pedal sinks. allowing plenty of stopping distance during driving, if i pump the brakes 2 or 3 times, the brakes get better but not any where near the way they are supposed to be. please help, Joe

I would suspect the power brake booster has died. Let the van run a few minutes then shut it off. Wait 30 seconds then apply the brakes. You should get fair pedal resistance for at least 2 or 3 applications. Could be it's vacuum source is leaking. Inspect the vacuum line going to it for cracks.

Have you checked your rear brakes? I have a 95 Chrysler cirrus and had similar problem. I changed the master cylinder,but still had the problem.
Jacked up the rear wheels and pulled the drum on ,yes drum brakes in rear,rear brakes and notice that the seals were really dirty cleaned and found a hair line crack on the rubber seal that the brake line connects too.
went and purchased the 2 seals, one for each side, and cleaned area and replaced!! Put everthing back and what do you know,the brakes worked great!!
I hope this may help !!!!