Tim, I thought you should know this. My 55 doesn't make that sound!!! I looked up the system in my 58 Chiltons auto manual. It states that there is a vent into the cab right below the power unit push rod. It has a filter on the vent. It could have some mud or something over it partially blocking the air intake to the diaphragm. It also show a test to check the vacuum unit. It says to push brake peddle several time until all vacuum is out of the system. Hold brake on and start engine. The peddle should move forward once vacuum his the booster. If not you have a problem. RC Billings, Montanaaaaaaa --- Tim Hulse <thulse@xxxxxxxxxx> wrote: > Well guys, Imperial number lll is in my hands. I > took the newly aquired > 55 out a couple of times for a cruise and I have to > say. It was like > rideing on a cloud. It is 55 4-dr sedan with A/C > (not working yet). The > engine is very quiet and it shifts smooth. This one > once belonged to > another member and he had done a lot of work on the > brakes so at least I > wont have to tackle that. There is a hissing coming > out at the brake > pedal only when applied. Any easy fixes for that? I > know it was rebuilt > not many miles ago. > > Tim Hulse > 1955 Imperial > ===== RC Billings, Montanaaaaaa http://www.imperialclub.com/temp/1955/RogerCrabtree/ Find local movie times and trailers on Yahoo! Movies. http://au.movies.yahoo.com