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Old 04-04-2000, 09:27 AM
stevebfl stevebfl is offline
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Now for the questions.

Would the bad diaphrams allow for a drop of 5 inches Hg while the engine is running?


Which door do the trunk and fuel door locks operat from? I know the driver's button operates the vaccum switching, but do the trunk/fuel door lock lines come from the right rear?

The two systems "lock" and "unlock" are like a tree. The lines branch off for each door and element down the right side. The left rear door is the first branch before the system passes across the dash. (I presume we are talking a 108 chassis here). The lines go along the inside sill moulding eventually going into the trunk.

Also, how many vaccum lines should be running to the fuel door latch? Mine only has one I'm thinking, being at the end of the line so to speak, the fuel door only had one line, the vaccum supply to activate the lock. When the vaccum is removed, atmosphere allows the latch to retract. Am I right?

Sort of. The gas flap has one line because it works against a spring. The spring moves it to the opposite position when the vacuum goes away.

And lastly, for now, when in the door panel, I hooked up the vaccum gauge to the supply line at the actuator. When teh driver's button was pushed the gauge showed about 1 inch Hg draw. Is that sufficient to cycle the actuators?

The further down the tree you go the more your vacuum is going to look like the problem than the source. No 1in isn't enough. The technique you used in vac testing at the source was appropriate. Now you must take it the rest of the way.

The first step (this holds for all two line "vacuum only" systems)is to identify the resevoir line. After verifying that it is tight (as you did) disconnect and plug the line to the reservoir. You want to tee into the line that goes to the master switch (the other line under the hood) and monitor the system without the reservoir (this magnifies the visual effect of the leaks - they are easier to see). Try both lock and unlock to see if the leak is in only one side.

Then approach the side that leaks the worse. On 108 chassis the lines were available through the removed glove box; you can cut and reconnect with rubber if no junction is found. Disconnect and cap. This removes the whole right side. Verify the tight system. If there is still a leak check master valve or left rear door. If there is no leak, reconnect the system and go to the trunk, disconnect and cap the incoming line. Does it still leak. Cap off every leak as you find them and keep eveluating untill you have no leaks.

The later cars have all the junctions available by removing either carpeting or sill covers, but that old car is probably harder to get to the junctions than to remove both right side door panels.

Besides, I recommend replacement of the vacuum door servo in bulk, especially if you are paying for the diagnosis. The problem with just fixing the one that is bad is: because the system has been running at lower levels of vac when the system is restored the rest often fail quickly under the new load requiring further diagnostic costs and eventual replacement anyway. Because of the ease of diagnosis and their different evironment the trunk elements don't need to be incuded in this bulk replacement.

Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician
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