Diesel Jeff

Lately I have been noticing a hissing sound coming from the driver's side under the hood. The noice goes away instantly with the slightest tough of the brake pedal, then comes right back after releasing the brake pedal. What is this? How can it be fixed? Is it something in the brake boost? Please help.

Thanks.

-Jeff

HotRodTodd

Yes , more than likely the booster is leaking, or a vacum line is rotted or just loose.

Jer12377

On mine (93 w350) there is a vacuum sensor under the hood hinge on the driver side. Check that also.

14racing

We had one that did that and the booster was bad.

Diesel Jeff

can a bad booster be fixed? What is involved? Where are the vacuum lines that I am looking for?

Ezra

Intercooler boot?

wannadiesel

Replace it, along with the master cylinder. The reason for this is that most bad boosters go bad because brake fluid leaked out of the back of the master. Booster rebuilders will not warranty their booster unless the master is replaced at the same time.

The vacuum line runs up from the pump to the booster. It's a 3/8" line with some big foam insulation on it. I don't think it's your problem, but checking it is free.