Any way to test an engine vacuum pump off an engine? - PeachParts Mercedes-Benz Forum

jmbeam · #1 09-03-2012, 09:12 PM

I was not getting any vacuum off my vacuum pump from my 1994 S350D. I removed it in anticipation of replacing it. I have been searching for a used one which has been hard to locate. A new one costs over $300.

Can my old pump be tested to definitely confirm it does not work? Someone told me that these rarely fail. With that said a fellow emailed me back pictures of a pump off a 1987 SDL. It looks dirty and old which is most likely correct because if its original its 24 years old! Now Im thinking that even though this pump with posted will cost me $110 if I am being penny wise and pound foolish purchasing such an old pump?

pawoSD · #2 09-03-2012, 09:22 PM

Using an old pump is indeed foolish. They can fail and take out the engine. Spend the $300 and replace the pump, not worth destroying the whole engine. $$$$

sixto · #3 09-04-2012, 12:10 AM

This is one way to check an old style pump -

This pump was operating normally but was replaced out of caution. It's still in my garage.

Sixto
87 300D

sixto · #4 09-04-2012, 12:11 AM

With the old pump out, take a picture of the IP timer to get an assessment of the roller coaster track cam that drives the vacuum pump.

Sixto
87 300D

pawoSD · #5 09-04-2012, 12:24 AM

I replaced the pump on the OM601 engine I put in my 190 recently out of precaution. The old pump was fully intact, but I am not gambling for $300, the engine/pump have 232k on them. New pump design is superior, with the balls enclosed in steel.

jmbeam · #6 09-04-2012, 10:30 AM

The two pics you posted look the same, you say the cage is gone on one. I don't see it could you point it out? I must have the newer style because my bearings are enclosed.

Anyway to test this part while its off the engine?

Jim H · #7 09-04-2012, 11:16 AM

Notice that the balls are evenly spaced in the top photo, and are clustered around the bottom half in the lower photo. The "cage" is a spacer to keep the balls evenly spaced. Without this cage the balls are free to run around randomly, bumping into each other, and failing to support the side that they have abandoned.

ROLLGUY · #8 09-04-2012, 11:44 AM

Unlike the VP's on the iron head engines, the VP's on aluminum head engines are said to be not rebuildable. They also have a tendency to leak, and when they do, replacement is the only option. As others have said, a new one is your best bet. I sold a used one to a guy that tested it by using the handle of a screwdriver to tap around the outside edge of the cover. I guess if a tap sounded more hollow than the others, it would suggest that a leak is there. The guy said it seemed good and bought it. However, $300 is a lot of money, but it is cheap insurance for your engine.

jmbeam · #9 09-04-2012, 12:08 PM

OK now I can tell the difference. My Vac pump has sealed bearings and to be honest looks real good. Is there a way to blow air in these to tell if its any good. I just want to confirm for sure this pump is bad.

jmbeam · #10 09-04-2012, 12:32 PM

Could a bad gasket around this vac ump make it appear that the pump is bad? Please does anyone know if there is a way to test this vacuum pump when its off the engine?

ROLLGUY · #11 09-04-2012, 12:37 PM

Quote:

Originally Posted by jmbeam

Could a bad gasket around this vac ump make it appear that the pump is bad? Please does anyone know if there is a way to test this vacuum pump when its off the engine?

You can lay it flat on the floor and push the roller downward with your finger on the vac connection. It will take a lot of force, but you will be able to tell if it will hold vacuum right away (1or 2 cycles). You could also rig up your vacuum pump to the connection.

jmbeam · #12 09-04-2012, 12:57 PM

OK I pushed down on the roller and there was a vacuum. Does that mean its good? If so now Im puzzled why there was no vacuum when it was on the car?

When I took it off the gasket was broken, could that do it? I mean there was NO vacuum when I tested it.

Junkman · #13 09-04-2012, 01:57 PM

Did you block all of the other vacuum ports when you tested while installed? A friend of mine had a shop misdiagnose a bad vac pump when the brake booster was bad. He has a 240D which only has 2 ports off the main line to the brake booster.

Brakes were working but car wouldn't shut off. New vacuum pump didn't fix it and didn't show vacuum. It did have vacuum with the brake booster out of the equation.