Just want to get my thought process verified by a few of the brains here...

Have recently been getting the following symptoms:

Engine shutting down more slowly than normal with key shutoff.

Occasionally (very rarely) the brakes will go hard, as if the booster is suddenly not getting vacuum.

Findings:

- oil definitely being sucked up into vacuum line to Injection Pump shutoff valve.
- bit of oil now dripping from ignition switch vacuum lock fitting. (got a couple of oil drops inside car to prove it!)
- Vacuum at brake booster line 'T' fitting reads 20"
- Vacuum applied directly from brake booster line 'T' fitting shuts the car down pretty quickly.

Vacuum systems in these old diesels have been discussed exhaustively here - and I've read virtually all of it!

So I'd just like to test my thinking here:

1) Oil in IP shutoff valve vacuum line is pretty much diagnostic of leaking diaphragm, right? Time to replace.

2) Will oil in the ignition vacuum lock do damage to it? Am I likely to need to replace this, too?

3) Is 20" of vacuum adequate, or indicative of a weakening vacuum pump? I have a rebuild kit around somewhere...

I've also sourced the bearings for the vacuum pump, in anticipation of rebuilding it at some point. Is now that time?(!)

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'83 300 SD
'68 Triumph TR 250 - The only car I ever loved more than the Mercedes; who needs electricity, anyway? - Damn, why did I sell it?!
'59 Jaguar 3.4 'Le Chat Noir' - Damn, why did I sell it?!

It's difficult to make predictions, especially about the future.
- Niels Bohr

Yes, If oil is getting up into the Ignition Switch the Diaphragm is leaking in the Vacuum Shutoff in the IP

I have not read of anyone say the Oil damaging the Ignition Switch.

As a temp measure you can put a plastic fuel filter in the vacuum line between the Vacuum Shutoff on the IP and the Vacuum Shutoff on the Ignition Switch. That way the Filter will catch the Oil before it gets up their.

It is also possible you have more then one vacuum issue. It would be nice to check the Vacuum Pump vacuum all by itself to see what it is putting out.

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84 300D, 82 Volvo 244Gl Diesel

20" of vacuum is sufficient. I would not recommend rebuilding the vacuum pump. I have a friend with a 1985 300CD who rebuilt his own pump (new bearings, etc.) and 3 weeks later his pump exploded internally and took out the timing chain, camshaft, camshaft towers, etc. essentially the whole engine. New vacuum pumps are around $350 and are well worth the money. I now change mine every 150,000 miles as a maintenance item. Cheap insurance.

The shut off valve on the ignition switch is cheap (less than $25) and easy to change.

Replacing the Vacuum Pump with a new one can also be a more complex issue. T

There is a Bushing in the timer that if it is worn out will ruin a new Vacuum Pump and risk that parts from the Vacuum Pump falling into the Timing Chain and Gears.

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84 300D, 82 Volvo 244Gl Diesel