hissing sound under dash

[oshea]

hi all,
well i sorted the alternator and its charging now but i have now noticed a hissing noise,
my car is a r129 sl300 ,when the car is started i can hear the hissing coming from the drivers side behind the clock area.
any ideas please?

 

[carat 3.6]

Could be a loose vacuum pipe.

 

[dinoy]

everything works on the clocks noise get worse with speed elborate pls

 

[oshea]

hi,clocks work fine,(speedo reading slow though but its a replacement set of clocks i put in yesterday there is no increase in loudness of the hissing when reving etc,it seems be either behind clocks or the panel under steering wheel.
i will remove both today and check for pipes off etc

 

[grober]

Almost certainly a vacuum leak. Several components are driven off the vacuum produced by the engine inlet manifold vacuum- headlight leveling and the heater control flaps for two. It's important to track this down as it may result in a weak fuel mixture. The nylon pipes are usually OK its the rubber connections that usually perish or crack- these are not immediately obvious to visual inspection but this is where your ear comes into play. For testing more complex vacuum components/problems a vacuum pump like the mityvac can be handy.
http://www.amazon.co.uk/dp/B00265M9SS/?tag=amazon0e9db-21

[YOUTUBE]eZn2uccojVA[/YOUTUBE]

this is a good r129 video compilation Mercedes r129 500sl repairing a loose, door mounted power seat control panel - YouTube

 

[zenman63]

Could just be Low air con gas.

 

[Sp!ke]

It sounds like a vacuum leak from the headlight adjuster. A cheap and easy fix.