Hi there, Im diagnosing my vacuum line problems, (hard shifting, door locks not working, centre vents not blowing...) and Im following DieselGiants little tutprial on testing the Vac system. Mercedes Vacuum Troubleshooting

The first thing to do was testing the main vacuum line by disconnecting it form the brake booster and testing vacuum from the line. His gauge shows about 22Hg (and mentions it should be a little higher due to the gauge not making a snug fit)

I tested mine in the same manner and its showing about 16-18Hg and climbs when I rev up the engine to about 25Hg max. This seems a little low to me, am I right?

Next step Im told is to verify vacuum from the check valve from the pump. I cant seem to find any good description on how to do this or where the check valve would be located. I guess I need to do a diagnosis on the vacuum pump. Can anyone help? how do I test this thing?

Thanks
Michael

I believe its located between the pump and the plastic line.

Item #20.

Attached Thumbnails

 

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83 SD

84 CD

great thanks, So to check it properly, Ill have to see if it holds a vacuum? or just see if it allows air to pass one way only?, and to chek the pump? I guess hook up the mityvac right to the pump and look at the pressure there

It should only allow air to flow in one direction, toward the pump.

After shutting down the engine, listen closely at the pump and booster, you may be able to detect a leak.

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83 SD

84 CD

check page 43-023 of the manual, it gives instructions on how to test the check valve

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1981 NA 300D 310k miles

^ There ya go.

Attached Files

vac check valve test:43-023.pdf (164.8 KB, 135 views)

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83 SD

84 CD

Thanks!

When I had trouble with Mine spraying out the Valve with WD-40 cleaned the Gunk out of it and it has continued to work for at least 4 years now.

Don't use Brake Cleaner as the Valve inside is Plastic and Brake Cleaner make some Plastics gummy.

When others have removed the Valve they had reported the part were broken or the guts of the Valve were entirly gone.

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84 300D, 82 Volvo 244Gl Diesel

i just reread that page in the manual, its kind of ridiculous to create that tool they say to use. i bet you can just "T" into one of the lines coming off the brake booster line to get the same effect, or find a way to attach the vacuum gauge directly to the check valve

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1981 NA 300D 310k miles

The reason for the made up Fittings is so you don't have to cut through the Plastic Tubing on the Main Vacuum Line.

You could easily do this on Mine because I removed the Plastic Tubing and replaced it with Rubber Hose and that also allowed Me to route the Main Hose more on top of the Fender Well.

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84 300D, 82 Volvo 244Gl Diesel

The Check Valve test that is in Post #6 is for testing the Plastic Check Valve that part of the Main Vacuum Line.

It will not test the Vacuu Valve on the Vacuum Pump itself.

On the last page at the very bottom it has that if the Check Valve does not pass the test to reaplce it along with the Vacuum Line. It has nothing about replacing the Check Valve in the Vacuum Pump itself.

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84 300D, 82 Volvo 244Gl Diesel