Vacuum leaks
 

Over the years, one of the most common and annoying repairs and in total, an expensive one is chasing down vacuum leaks.

What is the most common cause of vacuum leaks? Is it breaks in the lines or loose fittings?

I want to start fixing these myself because it does not look too hard, just time consuming and I need to know what to look for. Thanks

I have a 77 240d and 80 300sd.

Any of the rubber components can crack-door lock actuators, climate control pods, connectors, tees, etc. Or connections can get knocked loose. But I suspect that aging rubber is the prime candidate. There are also check valves in the system that can fail.

Since the door locks and the transmission, etc. are separate systems on the SD, I found it is much easier to just change all the flex fittings, at once, and go from there. It is not worth it to spend too much time trying to eliminate $2-3 pieces. Once those are changed out, if I still have problems, then I try to find the leaks.

Are there many of those flex fittings in a 116 body? Don't know how many to buy.

Thanks

OOPs!
 

I didn't note the date on your 300SD, which is indeed a W116. I'm not sure if the systems are separate on that series. On mine, a W126, there were (4) 3-ways and the (6)end pieces I picked up at Pep Boys I believe. Yours may be different and I don't want to steer you wrong. I just poked my head under the hood and counted them. Fastlane carries the 3-ways.

I've had plenty of both, the rubber connectors ageing, and breaks in the hard plastic lines, specifically the one going to the front passenger door for the lock at the hinge, and the one that fed to the EGR where it crossed in front of the block, it took fixing about nine connectors and two hoses to get the engine to finally shut off on its own :rolleyes:

Thanks for the responses. I asked because I have never done this before and recently, my mechanic had fixed some leaks. Less than a month later, the passenger door stopped locking with the others.

At that point, I thought about learning to do it myself and while the car is apart, replace everything visible that might be likely to fail soon.

I just did not know where all of the flex fittings were located. If they are all under the hood, I will count them and get whatever parts are needed to start there.

They are under the hood, in the doors, behind the dash, in the trunk and on the transmission! It seems like the under hood ones are the worst because of the temp in there. You have a Mity Vac yet? Without it its like looking for electrical problems without a multimeter.

I tore my console out to test the check valves for a leak "before" I recalled that the most common leaks often take place in the vacuum bundle that runs alongside the battery. Battery acid will get inside the bundle and eat the plastic vacuum lines. Mine had several that were eaten by acid and I had erratic climate control problems. I spliced them and now everything works fine.
You do need a Mity Vac to troubleshoot this system along a vacuum guage and some golf tees to plug lines as you troubleshoot.
It took awhile but I also found my defective trunk actuator.
It is time consuming but worth it to me after paying $400 to have an independent fix vacuum leaks.



1980 300D