Vacuum Trouble Again - PeachParts Mercedes-Benz Forum

kenstfelix · #1 01-30-2016, 02:41 PM

So here's my story. I have a 1980 300d non-turbo. I replaced the vacuum pump with a rebuilt one about a year ago because I was getting oil in my air filter and it seemed to fix that problem.

Yesterday I started having troubles again. It started with my brakes not feeling right - I would have to press much harder. It seemed like the car was starting to take an extra second or two to turn off. I had this problem awhile ago and fixed it by completely blocking the vacuum to the windows and trunk.

Then I drove a couple hours home. Brakes were feeling weird and when I stopped for fuel the car wouldn't shut off. Then the transmission started to shift late. By the time I got home the heat wasn't blowing (servo is bypassed).

I wonder if it's the pump again? I checked the oil filter and there was a little oil in there but not much. Or I wonder if it's the brake booster since the problem seemed to start there.

Anyone have a suggestion as to how to go about trouble shooting? Is there a way to test just the vacuum pump itself? Thanks!

optimusprime · #2 01-31-2016, 04:54 AM

Take a pressure test from brake booster .

ROLLGUY · #3 01-31-2016, 12:12 PM

You need to test the pump with your MityVac (or other brand vacuum tester). If you find good vacuum from the pump, the problem is elsewhere. Isolate one component at a time to find out where the leak is. To test the pump, remove all vacuum lines from the main supply tube, and connect your vacuum tester before the check valve (valve close to the brake booster end of the main line). Remove the fitting from the brake booster and cap it off somehow so all the vacuum is going to your tester only. If you have 20 inches or so, your pump is good. It also may have a bad check valve (the main line screws into the check valve on the vac pump).

kenstfelix · #4 01-31-2016, 03:22 PM

okay i'm going to get a vacuum gauge to test the pump. i have a little mity vac pump and tried to test the booster. it was holding at about 5 hg. not sure how long i need to pump it.

ROLLGUY · #5 01-31-2016, 07:43 PM

Quote:

Originally Posted by kenstfelix

okay i'm going to get a vacuum gauge to test the pump. i have a little mity vac pump and tried to test the booster. it was holding at about 5 hg. not sure how long i need to pump it.

The mity vac is what you need to test the system, so no need to "get a vacuum gauge to test the pump" other than the gauge on the mity vac itself.

kenstfelix · #6 01-31-2016, 09:11 PM

ah, ok thanks.

kenstfelix · #7 02-01-2016, 08:48 PM

so i unhooked the line going into the brake booster and plugged my vacuum pump in there. i also plugged up the two ports off the main vacuum line. then i turned on the car and... zero vacuum.

this sounds like the correct procedure, right?

ROLLGUY · #8 02-02-2016, 12:02 AM

Quote:

Originally Posted by kenstfelix

so i unhooked the line going into the brake booster and plugged my vacuum pump in there. i also plugged up the two ports off the main vacuum line. then i turned on the car and... zero vacuum.

this sounds like the correct procedure, right?

Yes, sounds like all the available vacuum is going to your gauge, and no leaks. If it is in fact zero, you have a bad vac pump or maybe just the check valve.

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