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Vacuum line diagram
Quite a regular
2017/9/29 18:30
From Babylon NY
Posts: 47
Hello All
Is there a diagram of the vacuum line routing and connections under dash?
I have a loud hissing sound coming from under the dash when I start the car.Definitley sounds like air leaking and stops soon as engine is shut off
I hear it in the area of the rear heater control

Posted on: 5/22 9:55:35
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Re: Vacuum line diagram
Forum Ambassador
2007/4/20 17:54
From Fresno CA
Posts: 15115
About the only all on one page factory vacuum diagram is plate 42 in the 55-6 parts book. There are partials which can be compared to get another idea of the complete system. The windshield washer instructions in the accessories section of the SM is mostly a repeat of the parts manual but gives a more realistic view of the way hoses actually run. The wiper description in the instruments section of SM covers the dual vacuum supply in better detail only omitting the metal tubing coming from the intake manifold and aux pump. If the car has a rear window wiper that layout is shown in the accessories section of the 51-4 manual. I don't believe anything else used vacuum in 55-6.

On a 55 400, if the car is typically equipped the only vacuum that is under the dash is at the wiper switch in two small hoses going to the sweep control on the wiper motor. You could have a hose loose or broken or, if the hoses are reversed there will be a hissing noise if the lever is turned to one position but will go away if the lever is moved to the other. If your noise goes away by moving the small sweep lever under the knob just reverse the two small hoses either at the switch or more easily reached, at the wiper motor.

If those small hoses are OK and the sound is loudest on the right side possibly one of the hoses at the balance valve on the engine side of the firewall is the problem. It could be the noise is just being heard thru the nearby heater and passenger side vent openings.

Posted on: 5/22 10:29:01
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Re: Vacuum line diagram
Quite a regular
2017/9/29 18:30
From Babylon NY
Posts: 47
Thanks for the great info it was the wiper sweep control hissing problem solved .

Posted on: 5/26 7:22:26
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