I have been tracking down the leaks in the door lock system on my 1983 300 CD and replaced the leaking actuators. The system works great for several hours after turning the car off. However, it will not hold a vacuum overnight. Obviously, I have a very slow leak somewhere. I have a couple of questions, first should I expect to acheive holding a vacuum overnight and second any tips on finding very slow leaks in the vacuum. All the actuators have been replaced with new ones recently, as well as, the check valve.

Thanks for your help.

John Fenn

What about the seat back locks? They work on vacuum too. The elements also leak!

Check them out, also see if the vacuum release button is not leaking (by taking the seatbacks off)

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2008 BMW 335i Coupe

The seat locks are next on my list. They leak so bad that I have had to isolate/disconnect them from the system at this point. I am just focusing on the door locks at this time and while they work great for several hours, they will not hold a vacuum overnight.

Thanks,

John Fenn

Get up at 4:00 AM. Start the car and run it for 2 minutes so you have vacuum for the morning.

But seriously, this is where a MityVac with a gauge becomes invaluable. Isolate the branches and pump them down just a tiny bit until the gauge needle moves. Watch for the needle to sink back down and you'll have the culprit. Don't use a deep vacuum because that tends to draw the components together and make the crack smaller so it leaks less.

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Rick Miley
2014 Tesla Model S
2018 Tesla Model 3
2017 Nissan LEAF
Former MB: 99 E300, 86 190E 2.3, 87 300E, 80 240D, 82 204D Euro
Chain Elongation References

I've fixed a few vacuum leaks on my car. The thing is 23 years old, and I've never had to replace an actuator. The leaks have always been due to a vacuum line cracking in a door jamb. The lines get old and brittle, so opening & closing the doors will eventually cause them to break.

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'79 300SD W116