Nissan Repair: nissan quest brakes fail, vacuum booster, vacuum line

Question
HI Thanks so much.  The brakes will go down one single time initially while changing from park to drive, then are hard to push down for about a minute untill car warms. Does this sound like the master cylinder or the the  diaphram etc. We have had the check valve checked

Thanks I should have been more specific about this initially

Melinda
-------------------------------------------
The text above is a follow-up to ...

-----Question-----
HI we have 2002 nissan quest minivan with 20,000 miles. We bought it 2nd hand and it has driven well for 1 1/2 years. However this winter when you start it the brakes will not work until the van is warm. We idle and rev for about 40 seconds to a minute and then it is fine. A mechanic changed the vacuum hose but that did not work. He then told be all cars have brake failure if you take of immediately and use the brakes right away ( we are not going back to him!!!)

The brakes worked fine last winter and we live in CA so it is not that cold. Help it is scary if you take off  and forget to warm up only to find you cannot stop at the corner.

Thanks
Melinda
-----Answer-----
Melinda,

If the brake goes to the floow when you first start then the master cylinder is defective.  If the brakes are just hard to press when you first start out then the check valve on the vacuum booster is defective or the diaphram on the booster is defective.  I would think the check valve first.  you see, that large black drum on the firewall that the master cylinder bolts to is a large vacuum canister and has a rubber diaphram in it.  There is a check valve in the hose that goes to the intake.  If the check valve goes out then the vacuum has to build up on the brakes.  Also, if the hose is cracked or does not have clamps it will leak down too.  Check it out and email me back.

Answer
Melinda,

A couple of things here.  First, I would think the vacuum booster should be inspeceted.  With the car off for several hours pull the vacuum line from the booster and see if you get a sucking sound.  That would mean the booster and check valve is good.  If no sucking sound you should replace the check valve first.  It that does not do the trick replace the booster.  Have the brake system bled with fresh brake fluid.  I like Ford High Performance Brake Fluid as it has twice the boiling point of regular DOT3 fluid and will not harm the ABS.  If that does not correct the problem replace the master cylinder.  If the master cylinder does not correct the problem the calipers need to be inspected for being stuck.  There is no brake light coming on or ABS light?  If there is you will need to have the code read before you proceed.  I am telling you the way I would proceed from the most likely to the least as well as the least expensive to the most expensive.