Vacuum element leaks in car, tests fine when uninstalled
 

I was having the typical vacuum system leak problems in the 82 300D, slow locks and slow shutoff, so I broke out the vacuum tester and started testing. I got to the trunk element and tested it by removing the lines from the Y-connector where the fuel filler door is and testing from there. Tests showed that the element was leaking, so I removed the element from the trunk and tested it. Removing the element and testing it showed NO LEAK. I decided that the must be in the hard yellow lines running from the Y-connector to the element. I tested both lines and found no leak. This is weird, there's no leak in the lines running to the element, and no leak in the element unless it's installed and hooked up. Why in the world is the element only leaking when installed?:confused:

Maybe one of the nipples on the actuator is cracked and when it's installed the lines stress it enough to cause it to leak, but when the lines are off the stress is gone and the leak goes away. Kind of a stretch but you never know.

I had the same problem diagnosing vacuum system in my car... The culprit was a hairline crack on the hard plastic line that would leak when in the car but when it was on the test bench (straightened out) it didn't leak.

Heres a tip that saved me a lot of frustration:

take a big bucket, fill it up with water and test to see if the line leaks air when you blow on one end. If theres a hairline crack you will see bubbles from the source. You can also test the rubber connectors but dont try it with the vacuum pod.

Seems like a drier way to do that would be to cap off one end of the line and try to pull vacuum on the other side, right?;)

I'm with Andrew. Either the bolts that hold it on or the pull/push of the lines when installed are enough to open a small crack and let it bleed.

I finally got around to testing the lines again today. They held vacuum, no cracks, so it was back to the element. It starting holding vacuum while installed, but I'm probably going to just dump it and get a new or slightly used one because now I can't get it to operate in unlock mode. Vacuum to either side results in a locking motion now for some reason. I also discovered a crack where the mounting screws go in. Oh well.:rolleyes: