Vacuum Pump Quagmire W123 - PeachParts Mercedes-Benz Forum

CaptKirk · #1 01-22-2014, 02:40 PM

Back on Jan 4th, my car began loosing vacuum during the course of the morning. That's also when a VERY cold front came through here. I went over to VSTECH's house of pleasure whereby I found him and Jaybob underneath a 300TD freezing their butts off. John confirmed what I had already checked with my Mityvac, that my pump was pulling about 10-15 inches of whatever the hell it pulls. There was a pump on a block, but two bolts were stripped, so I put it off til later, as it was very cold. I worried about VP detonation, since I have seen the 300 SD over there with a hole in the valve cover. By the following Tues, all vacuum suddenly became restored. The car actually shuts off faster than before. I tested it and the gauge read somewhere between 22 and 25, without any fluctuation. This pump is not the original - I replace it when it went bad - there is a chunk missing (I still have it, for forensics I suppose) from the area that contacts the fuel distribution pump timing do-dad (and didn't destroy my engine) with a unit off an SD from pull a part in Charlotte. My theory is the SUDDEN drop in temperature we experienced that day. Of course, I could be full of crap too. Thoughts anyone??

Diesel911 · #2 01-22-2014, 03:24 PM

Quote:

Originally Posted by CaptKirk

Back on Jan 4th, my car began loosing vacuum during the course of the morning. That's also when a VERY cold front came through here. I went over to VSTECH's house of pleasure whereby I found him and Jaybob underneath a 300TD freezing their butts off. John confirmed what I had already checked with my Mityvac, that my pump was pulling about 10-15 inches of whatever the hell it pulls. There was a pump on a block, but two bolts were stripped, so I put it off til later, as it was very cold. I worried about VP detonation, since I have seen the 300 SD over there with a hole in the valve cover. By the following Tues, all vacuum suddenly became restored. The car actually shuts off faster than before. I tested it and the gauge read somewhere between 22 and 25, without any fluctuation. This pump is not the original - I replace it when it went bad - there is a chunk missing (I still have it, for forensics I suppose) from the area that contacts the fuel distribution pump timing do-dad (and didn't destroy my engine) with a unit off an SD from pull a part in Charlotte. My theory is the SUDDEN drop in temperature we experienced that day. Of course, I could be full of crap too. Thoughts anyone??

Since you did not lose all of your Vacuum it could be the Check Valve that that screws into the Vacuum Pump Housing.
It can be removed and cleaned. I don't recommend Brake Cleaner for that as it can soften plastic parts.
I had a low Vacuum issue and removing and spraying out that check Valve with WD-40 fixed it and many Years have passed since I did that.

As for the temp related issu. This is the first I have read of that. Hopefully someone else will know.

tangofox007 · #3 01-22-2014, 03:45 PM

Odds are good that the pump inlet check valve has come unglued. The parts rattle around and intermittently block air flow, then rattle around some more and restrore same.

You can verify that problem by removing the check valve (nipple) where the hard line attaches to the pump. If you can see through the nipple, you will need to fish the missing parts out of the pump inlet. (Look for three parts: a spring, a plunger and a plate.) For the short term, you can reinstall the empty nipple and drive.

CaptKirk · #4 01-23-2014, 08:55 AM

Thanks guys, those explanations make a lot more sense. If it wasn't the cold, I was going to assume the government shut off my vacuum to mess with me.