Vacuum Leak - Hissing Sounds

[RonCT]

Hi Guys,

I have w202 1998 C240. I have an irritating problem...

When I unlock the passenger doors, there is a hissing sound that comes from the passenger side front door for a few seconds.

After I start the car, there is a continuous hissing sound. When I turn the dial that adjusts the headlight angle 0-1-2-3 - on 0 there is a no hissing, and on 3 the hissing sound is very loud. I'm guessing a vacuum pipe has come loose or is leaking somewhere.

Does anyone know a way I can get rid of these sounds without having to dismantle too much of the dash and door?

Thanks in advance

 

[television]

This is the vacuum system on the car,,the pipes on the rear of the headlamps break or come off and this is why you can hear it behind the headlamp range adjuster and a popular fault, any other will be in the drivers door as that is used most

http://www.detali.ru/cat/oem_mb1.as...722.609722.698&GM=717.464&CT=F&Cat=45H&SID=80

 

[wireman]

Your door lock actuator is almost dead, if it fails completely your central locking will not work anymore, or at least will be a shade random as to which doors are locked or unlocked. The belows actuator is inside the door near the latch. An electronicaly controlled pump applies vacuum to unlock the doors and pressure to lock the doors, it will run until the pressure or vac reach the required level or about 15 seconds, which ever comes first.
They are fairly easy to replace and cost about £30.

Do fix it or it may become difficult to get in the boot or fuel cap flap, The fuel cap has a manual emergency pull handle (see the hand book for its location picture) but if your boot lock key hole is gunged up (not unusual) and the boot lock's belows bit wont work you will not be able to put fuel in.

The door lock system does not operate on the engine vacuum.

As Malcolm says the head lamp units are engine vacuum driven via a thumbwheel operated valve next to the light switch, look behind the lamp unit for a 4mm nylon tube with rubber joining pieces which can fail, again the belows inside the lamp unit can fail and leak, open the lamp unit and you will see the actuator its about 60mm diameter made of white plastic wiht a pipe on one side and a push rod on the other.

If you cant locate the leak by eye use a piece of hose as a stethoscope to find a more precise location of the hissing.

Once you sort out the lamp leak please get the beams set correctly (with the engine running during adjustment) or you may dazzle other innocent motorists.

Good luck

 

[television]

Just info on the vacuum pump in addition to wiremans post above.

If there is a leak in the system then as wirman said it will cut off in 15-18 secs.

On a no leak system the pump cuts in 3-4 sec via the bellows built into the pump,, when the system has a leak the pump has an electronic circuit that shuts it down within 15- 18 secs´,,running on this circuit as wireman says will shorten the life of the pump

 

[RonCT]

Hi Guys...

Thank you for this great info... you guys are all spot on. The hissing sound on the passenger door cuts out at 12 seconds.

I will have look for the accuator behind the haed lamp this weekend. I'm not sure about the door yet... although I did read a step by step guide with pics on how to remove the door panels. I think I'll also make some calls and see how much a belows accuator costs from MB dealership and also from a 2nd hand spares shop.

Will keep you guys posted.

 

[wireman]

A second hand door belows will also be a worn one, go for new about £30.
I'm not sure if your headlamp belows can be replaced without replacing the entire lamp, I have bodged a 201 unit with cling film glued (evostick) across the atmosphere side of the belows diaphragm, it worked ok, the same did not work on a door unit since it sees pressure and vacuum which peeled my "repair".

 

[barneyb]

Does any one of a similar problem with the seat backs not locking on a 300ce,I believe this is connected tothe vacuum . M y Headlight Height adjuster does nt work either .

 

[television]

I have put some details up Barney on your other post