Vacuum pump question - PeachParts Mercedes-Benz Forum

80300dbenz · #1 04-12-2006, 01:30 PM

How do I test out my vacuum pump ? Yesterday I unhooked the hose going inside the booster while the car was running. It was sucking like PHIT, PHIT, PHIT, PHIT, PHIT as if a gas car would be missing. It is supposed to be doing it like that or should it suck without any missing? Its a 1980 300D .

boneheaddoctor · #2 04-12-2006, 01:32 PM

Thats exactly what it will do. Without a place to hold a resivoir I.E. intake manifold on a gasser its going to go PHIT, PHIT, PHIT, PHIT, PHIT as you describe.

80300dbenz · #3 04-12-2006, 01:38 PM

so the pump is working properly ?

rhodes2010 · #4 04-12-2006, 01:46 PM

If you had a vacuum gauge to attach to that port you opened then
you could get a reading, 19 to 22 inches of vac I believe.

If your power brakes work, and the engine shuts off when ignition
key is removed then I would suspect that the vacuum pump is working.

boneheaddoctor · #5 04-12-2006, 01:51 PM

Quote:

Originally Posted by 80300dbenz

so the pump is working properly ?

YOu would need a guage to know if its pulling the required vacuum....as was mentioned..if it shuts off fairly quick...you have strong brakes then its a fair assumption its working close to spec.

80300dbenz · #6 04-12-2006, 02:20 PM

Well theres one more thing. My car had ben sitting for a couple of years so I flushed out the brake system and i was driving and the pedal went all the way down and i had no brakes then after a while i got them back but the pedal was very stiff. Also before my car was sitting all that time it would shut off on its own now need to manually do it. So perhaps it is my pump. what should I do replace it or rebuild it ? Is it a fairly easy job ? What all do I need to take out to pull out the pump?

vstech · #7 04-12-2006, 02:54 PM

go to any automotive or hardware store and buy a mity vac hand vaccum pump wtih a gauge.
disconnect the large line from the first connector and hook up the pump, the vac gauge should be reading mid to low 20's of vaccum. if not plan a pump replace, but I bet you have a leak somewhere.
John

rg2098 · #8 04-12-2006, 03:01 PM

Quote:

Originally Posted by vstech

go to any automotive or hardware store and buy a mity vac hand vaccum pump wtih a gauge.
disconnect the large line from the first connector and hook up the pump, the vac gauge should be reading mid to low 20's of vaccum. if not plan a pump replace, but I bet you have a leak somewhere.
John

If your vac is reading low, its most likely a rebuild kit (check valves in the front) and not an entire pump replacement. I was able to do the rebuild with the pump on the car with the fan shroud removed.

orthotomeo · #9 04-12-2006, 03:01 PM

It's likely you have a leak in your door, trunk or fuel door lock. That was my problem.

Do a simple test.
1 Start your car.
2 Lock the doors.
3 Shut off your car
4. Wait 1 minute and lock the doors.
5. do they all unlock?
6. repeat above starting with locked doors (leave unlocked for a minute and then lock again after a minute).

If only the drivers door locks or unlocks the problem is a leak in doors, trunk or fuel door. Much cheaper than replace a vacuum pump.

I ended up plugging my fuel door lock so it's always unlocked and my trunk so it's always locked and it stops right away.

rhodes2010 · #10 04-12-2006, 05:19 PM

Actually the cost of the 1980 300D vaccum pump diaphragm is not bad.
Maybe $20.
Easy to do.
I have done it two or three times over 22 years.
Not the same vac pump the started being used in 1981.
Maybe these are harder, I do not know.