Strage brake system on S10

Hi
My girlfrind has an S10 and it have some pretty wierd brake problems. Sometimes it just wont brake, the effect of standing on the pedal only corresponds to a mild braking...
We have had it checked on a autorised Chevy shop and they repaired the front calibers and put on new diskes and pads. The fluid is also new. So it ran for a couple of weeks and now the "abs" light flips on and off by its own lesure and again this evning the pedal was stone hard with no brakes.. after she relesed the pedal and stomped on it again the car came to a halt slowly.
What the heck is wrong with the car?
best regards Zigge (Denmark = bad spelling)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Zigge wrote:

Loss of Vaccum if it is power BRAKES

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Check vaccuum at brake booster, and check for EGR sticking if low vaccuum.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.