Is there a test for brake booster unit before I buy an rebuilt unit. have not found a rebuild kit yet. Any help Craig.

1st test - when you apply the brake, do you hear a hissing sound? If yes - new booster.
2nd test - With the engine off, apply the brake 3 or 4 time. The brake pedal should get higher with each pump. If no - new booster.
3rd test - After test #2, do not remove your foot from the pedal. Start the engine. The pedal should drop slightly and return to normal position. - If not new booster.
4th test - disconnect the vacuum line from the booster port. Plug all other openings. Attach a vacuum pump and apply 10 - 15 inches of vacuum. It should hold this vacuum for a minimum of 3-5 minutes. If not - new booster.
When you replace the booster (I just did this, again, yesterday), you will find it easier to get to the bolts under the dash if you remove the entire seat and drop the steering column. Remember to remove the air bag fuse and disconnect the battery before you drop the column. When you replace the nuts, use a couple of really long extentions, a swivel and a short socket with a little "sticky" grease inside the socket. The grease will help you keep your sanity by keeping the nut in place. There really is a place under the dash of C-4's that hides dropped nuts and bolts - once there, you'll never find 'em
Good luck
Subman

ThankYou Subman, I have booster out of car at this time will try vacumn. are you installing booster reman from Cardone? I"ve heard there junk, but i am having a hard time finding one not remaned by cardone any ideas? Thanks Craig

Unfortunately, this is the 4th booster I have put in my 91. The 1st one I bought from Chevy. It split in 13 months. The second, from AutoZone. It lasted 3 weeks. The replacement has lasted 1 1/2 years, but it's a lifetime warranty. I was pleasently surprised when I swapped out the last booster to find AutoZone had, apparently, switched suppliers.
The new booster has a metal casing, the pushrods seems more solid and is generally tougher. You might try AZone and take a look at the booster your local store has. For my $0.02, I would NOT recommend going to the stealership. The part is WAY more expensive and without any warranty
Now, if I can get the brakes to stop the car, I would be happier than h-ll. I have one of those Vettes that has the mushy brakes and have not been able to find why - yet.
I hope it helps
Good Luck
Subman

I have a metal booster that I bought online from piratejack.net. I haven't had any problems so far. You can check it out.

That and my recent c5 brake upgrade have greatly increased my stopping power.

Good luck,

Matthew