Mercedes vacuum pump

Why does this car need a fourth vacuum pump, the first one lasted 180k miles, the last one 3k miles? 1995 E300D

Are you buying NEW Benz pumps?? Today, the term “rebuilt” means “junk”…

It comes with the “pride of ownership” of a diesel vehicle.

Yes, and no, they are not Chinese either. Mercedes Benz contracts this particular item to Pierburg, a German co. Original “Mercedes” has never meant that Mercedes produced the part!!!

NONSENSE! I also own a 1981 Mercedes diesel with an excess of 600k miles, which has never needed the replacement of the vacuum pump. When I rebuilt that vehicles transmission it included factory recommended “updates” to the original design for what they, then, considered premature wear items (although I do not consider 192k mi “premature” for that kind of component.) It’s never been rebuilt since. Pride of ownership? Not anymore–the newest one I have, or will own, was a 1999 whose transmission literally exploded while I was coasting to a stop and with less than 90k mi on the vehicle.

If anyone has anything constructive to relate re: invisibly worn camshaft or inexpert replacement procedures by an otherwise competent mechanic, I love to hear it before I spend another $700-800 on a another replacement that should last, based on original experience, more than 100k mi.

I’m probably not going to be much help here as most of my diesel experience is with VW.
Bosch so it’s six of one, half dozen of the other I guess.

The only thing I could add is that it’s incumbent upon whoever is doing this repair to figure out the cause of the failure. A mechanic’s job should mean more than changing a part out repeatedly and potential causes should have been looked at very closely after pump failure number 2.

Just curious, but how are these pumps failing? External physical damage that can be seen?
Any chance the pumps have been good and the problem is a huge leak in a vacuum operated accesory instead? Cruise control, brake booster, etc.?

This pump serves the brake booster and only affects, additionally, transmission shift timing from a smaller aux port and is driven, as best as I can determine, off of the cam shaft. In the first two failures I simply lost brake assist and shift timing. On this most current failure, however, I lost those and can also hear a loud clacking noise that was not evident on the first two failures. I purchased both of these pumps online and provided them to the respective professional mechanics after reading the installation precautions which indicated the sensitivity of the installation despite an otherwise straightforward placement and ease of access to any would be do it yourself-er. The car is not yet disassembled, however, it got re assembled twice before with every apparent success, only to fail in a relative short order, progressively.

There is a trick to almost everything and I am now assuming that includes this particular job.

You really need to post this on an MB forum, you’ll have much more luck there on something this particular.

Sure. Do you know of one that is not controlled by Mercedes, is powered exclusively for advertisers or, cost CASH to utilize?

Have you ever computed the true cost per mile to own and drive this car??

Well, as I still own it, how would I do that? I once owned a '58 Porsche Speedster that I sold for 2000% more than I paid for it, 8 years later. How do you “compute” cheap thrills? This car handles nearly as well, has air conditioning, roll up windows (electric) and runs on free waste cooking oil from the local market’s Deli dept. It will also run on Bourbon, however, that doesn’t come for free and it doesn’t have the lovely Kung Pao chicken smell exhaust that the free fuel I use produces. Incompetence always costs you more and while I do believe in hiring the handicapped, you needn’t apply.

Without car in hand and a physical inspection of the problem I’m pretty much lost on this one.
It’s my gut feeling that there has to be an underlying reason for the pump failures; IF the pumps have legitimately failed.

I can pose a theory. If the pump is driven off of a camshaft lobe and since the vehicle has pretty high mileage it’s possible that the lobe driving the pump could be going flat; or has gone flat now that it’s clacking.
Hardened steel holds up very very well but eventually when the hard coating wears through and microscopic pitting starts the lobe can disentegrate pretty quickly.
Maybe a badly worn lobe has now become a completely gone one.

I would think it would be possible to use a dial indicator with a probe and measure the amount of lift on that lobe.
Keep in mind that while I’ve serviced a Benz now and then, I’m not by any stretch of the imagination a Benz expert. Just theorizing here based on mechanical principles.