Hi:
I'm new to the forum.
My sierra had the power booster problem about a year ago , auto engaging the brakes as I drive. After changing the booster all was well.

Sunday night I was on I-10 and hit the brakes suddenly and after that the brakes became erratic. Pulled the power booster a discover the plunger in the booster popped loose. Got a new booster and I discovered the front disk were working , the rear drum brake were not. Funny thing the new booster popped out the center pin again.
I replace the power booster and master cylinder , Bench bled the Master cylinder , installed all and bled the brakes ( RR , LR ,RF , LF. )
All brake work fine. But the ABS has a slight Problem.
At 40 MPH , apply brakes to engage the ABS , the brakes actually lock , if you attempt to accelerate your not going anywhere. depress & release the brake pedal , and off you go. I pulled the ABS Fuse and the brakes function normally. Put back in the ABS fuse and the same results.
No ABS or Brake warning lights (except when fuse is out).

I have read in some forums that the ABS pistons have to be reset via a scan tool, but after speaking with a few local mechanics , they said they never resent the ABS . Some were not even aware.
Any Suggestions would be greatly appreciated.

abs tests itself at every start. abs is difficult to bleed without a scanner though, did you turn the key on while bleeding?

If you introduce air into the system ABS has to be activated by a Tech II scanner during bleeding to get the air out of the system.

jwfirebird , No I did not have the Key on during Bleeding.
2kg4u Thats what I have read on another forum about a year ago .

Thank You

i did it on mine a few times without a scanner. i just left the key on.then went out and activated the abs a couple times, then bled it again with the key on. then it was mostly fine. on drums you have to make sure the adjusters are free and tighten them up to get good petal after that too

By "activate the ABS a couple times" JW means slam on the brakes on a slippery surface (wet, or gravel for example) to kick in the ABS. Then bleed the brakes. You may have to do that a couple of times, and even then you aren't 100% certain all the air is out.

Many have had success with this method.

Yup, it takes a couple of hard ABS stops with bleeding to work the ABS motor and valves.

It took a couple of times to get the ABS to respond in a normal manner , After the bleeding advise & the ABS activation method via jwfirebird , all seems OK.
I will do a test tomorrow again to assure all is well .
If I still experience the problem , A friend of mine works at a shop with the Scanner and he will scan the ABS.

THANK EVERYONE FOR ALL YOUR QUICK REPLIES AND HELP!
You Guys are A+

sounds good