I have finally got around to an initial try out of my rebuilt 1971 142. As part of the restoration process, I had my brake booster rebuilt. With the engine off, pressing and releasing the brake pedal seems pretty normal. With the engine running, if I press on the brake pedal, the brake pedal is slow to return to the full up position. It eventually gets there, but takes about 3 - 5 seconds. Its almost like there is no vacuum being applied to the back of the diaphragm when the brake pedal is released. I think the servo assist function is working; but, I can't be sure as I have not got the car going fast enough yet to really apply the brakes hard to confirm that I am getting servo assist.

I have read through the operation of the booster in the Volvo service manual. The manual write-up of the brake servo is a little obtuse, like something was lost in translation from Swedish to English and the diagrams showing the operation are a little fuzzy. It is also very brief and does not provide any guidance on trouble shooting. Can anybody offer up any suggestions as to what the problem might be?