Bad Brakes, gmc yukon, bad brakes

I have a 2003 gmc yukon. I have had it 2 and a half years and the brakes have always gone to the floor.  I have replaced the pads, rotors, and calipers on the front and back and no difference. I have also replaced the master cylinder. The brake booster seems to have lots of pressure and I have had many mechanics look at everything and no one can come up with and anwser. Any ideas? please email my with any thoughts.
Greg

Answer
    I have had customers with the same problem on the same truck.  It always ended up being a problem with the anti-lock pump/distribution block.  The symptoms mimic an old-fashioned bad master cylinder, but the pressure is escaping through the anti-lock mechanism.  Proper diagnosis will require a set of high-pressure hydraulic pressure gauges and the appropriate fittings to plumb them into all points of the system.  If it was me, I would take it to a dealer.  However, most dealers will want to remove the non-GM parts when they are fixing it.  They have some good reasons for doing this, but they are primarily fiduciary, not practical.  Every town has a garage run by a guy who just recently left his GM dealer tech job to open up his own shop.  Usually they think they can make more money on their own, and usually they can't.  Nevertheless, they are much more likely to accede to your wish to keep the existing good parts on the truck and just fix the problem.
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