Dodge Repair: 07 Dodge Caravan: spongy brakes, vacuum leaks, spongy brakes

Question
QUESTION: I've got a good one for you.  Been having trouble with spongy brakes.  Had my mechanic work on it.  He's replaced the master cylinder and has all new brakes all the way around.  The brakes are good for awhile and then they are spongy again. After raising the van up on the lift, the brakes are firm for awhile.  Then after driving for awhile, they get spongy again.  The van only has 27,000 miles on it.  If you have any ideas what to look for I'd like to hear them.  Thanks, Mike

ANSWER: Hi Mike,
Are you loosing brake fluid from the master reservoir? I assume there are no signs of leaks, nonetheless. Is there a question about the history of the brake fluid in the system?
Air in the system can cause this...has the system been bled properly? Has the ABS system been bled properly?
If there is no loss of fluid, then perhaps you are loosing the action of the power brake unit, possibly from a leak in the vacuum line from it to the intake manifold. That may feel 'spongy' due to a slight vacuum leak.
If I come up with another idea I'll let you know.
Roland

---------- FOLLOW-UP ----------

QUESTION: Hi Roland There is no leaks.And no vacuum leaks.But why when the van is raise off the ground and set back down the break pedal gets firm. Thanks Mike

Answer
Hi Mike,
The only thing that I can imagine happening is that one of the rubber brake hoses located between each wheel cylinder and its metal brake fluid supply line is fatigued and/or bulging. Those rubber brake lines get fatigued and can thus lead to unusual things like a dragging brake due to impeded back-flow through the lumin of the tube. When you raise the van the four hoses will all be flexed. You could try lifting one corner of the van at a time to see whether one such single-wheel lift temporarily cures the spongy situation, and also check to see if one of the wheels is noticeably hotter after you drive several miles at speed without using the brakes. If so, replace that brake hose and bleed that line. Let me know how this works out.
Please 'rate' my answer,
Thanks,
Roland