For work I've already rebuilt two laboratory vacuum pumps, one direct drive and one belt driven. Those have an inlet and an exhaust opening, as well as a ballast adjustment. So that got me curious, how does the vacuum pump of our diesel work? I don't see any "inlet" to suck air from, nor do I see an outlet. I'm guessing that the inlet would be the one that goes to the main vacuum line to the brake booster. Was this a good guess? How about the exhaust then? Do our pumps have "vanes" like these vacuum pumps?

As I've never taken my pump apart yet, I wouldn't know how it works. The rebuild kit is similar to the ones I've rebuilt, mostly seals, O-rings, etc.

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On my 1992, it's a small spring loaded piston that's being pushed back and forth by a combination of a cam and follower coming from the fuel pump drive gear in the front cover.

But I get you point about where is the exhaust dumped. No clue.

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BigBen

'98 E300 Turbodiesel 244 000km
RIP '92 300D 2,5 Turbo 632 859,4km due to engine failure

The line going to the brake booster is the inlet, the outlet is straight into the crankcase (A yellow line to the air filter on older models).

Thanks, that makes sense.

How about the innards of these pumps? Do they have rotors and vanes too? I'm know it's driven by the timing chain, right?

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Nope. It's a diaphragm pump that rides on a roller coaster track that's part of the injection pump's timing device. So, it's indirectly driven by the timing chain.

Don't forget the one-way poppet valves on the inlet and outlet.

Is this true for the 82 to 83 300D's? Reason I ask is the pics of the rebuild kits I've seen (online) for my pump does not include a replacement diaphram, only o-rings and gaskets.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked