603: noise from vacuum pump after engine stops- leaking check valve?
 

This hissing noise is ongoing for minutes after engine stops on my 300 SDL. Is this a leaking check valve making this noise?
I might think it is coming from the check valve that sits at the outlet of the pump feeding the thick 1/4" line to the booster? I have the newer type pump with the screw heads.

a)Has someone experienced that the check valve was faulty making noise
b)I can't find this part as a separate item for the 1987 300 SDL??
Is this check valve the same part as for the 617 turbo engine pump?
Martin

Maybe the threaded fitting is coming loose. Give the it a twist to tighten.

With the engine running, fit a vacuum gauge to the small nipple on the pump then to the nipple on the plastic check valve further along the brake booster line, then shut off the engine to try to isolate the leak. The stop level in my 87 300D stays down for days so I know the brake booster line holds vacuum for a long time after engine shutoff.

Enough older style pumps have become junk that someone should have a check valve to spare. Let me know how it turns out. Someone I know might still have the scrapped pump from the 93 SD.

Sixto
87 300D

Remove the Brake Booster Hose/Tubing and find something that will not leak to plug off the Chack valve. Start the Engine and run it for a while. Turn the Engine Off and Listen for leaks.

Thanks. I'll test the check valve. If I shut the engine down (...hear the noise) I can step on the brake- then the vacuum in the 1/4" line should go down rapidly. If the noise disappears then it might be this check valve.
I'll also test the smaller line with the gauge...see if it holds vacuum well.
Does anyone have a spare metal check valve?

When I had an issue with my Vacuum Pump Check Valve cleaning it out with WD40 got it to work.

That is a great idea. I have the valve out and put another valve in.
The sound has gone away. The sound definitely was the check valve.