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I have a 2006 chev. express van 1500. I put new brakes and rotors on it about 8 months ago and all was well until about a week ago. At the end of each stop it fells like the brakes let go. Kind of like I hit a small patch of ice, but this is on dry ground.  
  Thanks for any help.  

papher51,
I'm sorry to hear about this brake issue! I expect you'll get some great technical feedback from other users of the forum. As a customer service representative, I cannot help to diagnose vehicle concerns over the internet, but if you should like assistance in working with a dealership I'm available to you! Send me a private message if that time comes.
All the best,
Sarah
GM Customer Service  

this might be and probably is an antilock brake issue...

does the ABS light flash or come on at the exact moment this is happening..

you could have metal fragments stuck to the wheel speed sensors...

you could have rust build up or a cracked tone wheel on one or more of the wheels...


you could also have a damaged wheel speed sensor..

how the system works..  it has magnets with coils of wire wrapped around them..  and toothed tone wheels on the inside of the brake rotors or axles..    as the tone wheels rotate.. they generate a voltage in the speed sensor..   with each of the wheels moving at the same speed...  the voltage between the 3 or 4 sensors is the same...   if one wheel starts skidding.. that sensor voltage drops... the antilock computer sees that.. isolates that wheels brake hydraulic pressure and can release or apply the pressure to make the wheel at close to the same speed as the others...

where the system has faults.. is when the speed sensors get coated with metal filings from the brake rotors and pads wearing..

where the wiring to the sensors gets damaged..

professional mechanics and dealerships have diagnostic tools that plug in.. and can check for trouble codes with the antilock brakes.. to see if one of the components has been identified by the computer as to being out of expected normal operating range..

the better scan tools for ABS...  i don't know what the current versions at the dealer are.. but they used to have a TECH 2 ...  that a tech could plug in..  two techs would take the car or truck for a short test drive.. the passenger monitoring the multiple voltage readouts on a display that graphs the voltage..  so they can compare the signals from the speed sensors as they start and stop the car/truck..   its easy to see any problems will be easily diagnosed..

once in a while.. there will be a problem where one of the wheel sensors creates a higher voltage than the other wheels..  this causes the other wheels to be isolated and the brakes released to match the wheel that seems to be moving faster..

this is where the proper scan tool really needs to be used..

i am not hip on the current traction control systems as i normally work on the early 60s to the early 2000 model cars..  if they use the acceleration sensors to monitor the antilock brake function... for conditions on possible icy roads..  switching that function on when the exterior temp sensors show temps below freezing..  or sudden changes to the air temps as you cross black ice areas..

so... have the antilock/traction control system scanned for codes... have a mechanic take a short test drive while the wheel speed sensors are being monitored in graphing mode..   then a visual inspection..  of the wiring. at the wheels..

please note.. that when replacing brake pads..  one really does NOT want to retract the caliper pistons without knowing just how to open the bleeder screw while retracting them..  and close it before releasing the retraction pressure on the piston so you don't let air into the system..    this stops the corrosion and crud that forms from the heat baking the fluid in the calipers from being forced backwards through the very expensive antilock control assembly..


i realize that this did not answer WHY..  directly.. but i hope that this will help you get it fixed..

knowledge is power...

mechanical/hydraulic issues can still be problems with brake systems..  but it sounds like the antilock has a problem with yours..

post if you have more questions...

there are gm factory service manuals written for every model..

alldatadiy.com

and

eautorepair.net

both offer exact repair info to help diagnose what the scan tool shows.. and how to do the job..

also.. please post what happened when you get it fixed...  

to find this thread.. log in.. click the link above that says MY THREADS or book mark it...  so you can find it again..  

The only time the ABS light is on is during start-up. Scan at autozone showed a bad sensor. It couldn't tell which wheel it was on.  I took a long shot and went to a self wash car wash and sprayed the inner hubs as best as I could, just in case they has brake dust on them. So far after 4 miles of in town driving all is back to normal. I update tomorrow.   thanks a bunch.  

post the code it had... i have the list  of descriptions..