Brake Booster Question

We just replaced the brake booster on the 1970 Dart with a fresh 318 and a very (near factory) cam and it is not working. I have never had a new booster that was bad and want to be sure that I have checked everything before sending it back (partgeek).

I did the pedal test and it failed. The pedal stays the same and hard.

I pulled vacuum at the booster with a hand pump and could only get it to 14 psi but it held that vacuum for 5 min. I read that I should pull 20 psi to do the test but it would never go higher that 14-15. When I tap the brake it only drops 5-8 psi at a time. It does not go to directly to zero. I am getting about 15 psi from the engine at idle and it increases with the throttle.

Thank you for any input