Hi all. Although I've searched and used this forum probably a hundred times in the last month, I'm still sort of a newbie. I bought a 1985 MB 300D Turbo Diesel with 254k miles about a month ago. I knew next to nothing about diesels before buying the car, and I hadn't worked on a car in almost 20 years. Using this forum and the FSM, I was able to successfully: change all filters and the oil pan gasket, replace the primer pump, replace the front brake pads, perform a diesel purge, and check the vacuum system for leaks.

From the latter, I found that the pump was putting out only 10" of pressure, which I have read is very low. As a result, the engine is not shutting down properly and the transmission is shifting rather harshly. There are other vac problems too (door locks, a/c), but I think these are due to a leak somewhere behind the firewall. I'll get to those later.

I tried to inspect the pump check valve, but was unable to get it off. In searching this forum for help, I found several threads discussing pump breakdown and the devastating effects it can have on the engine. So I pulled off the vac pump. What a major PITA! There was caked-on oil and grease all over down there. I don't know if this is from the pump or something else. And whose bright idea was it to hide a bolt under the unit with a fan, belts, and a wire in the way?

When I inspected the pump, I didn't find any signs of breakage or pending breakdown. The rocker arm, spring, piston, and bearings are all intact. There were no metal shavings or shrapnel. Despite spraying the valve with lubricant, I am still not able to get it off. I did test it though, and it seems to be working well.

The concern I have is that the spring and piston are extremely stiff. I am not able to push them down at all. I read somewhere (here or other forum) that the piston should be relatively easy to move. With the one on my pump being so stiff, does this mean the pump is broken? Is there a way to loosen up the piston without a rebuild? Lastly, are there any ideas on how to get the valve off?

Any help you can offer is greatly appreciated. I have many other questions, but I will reserve those for future threads.

Averyphilly
'85 Mercedes 300D Turbo Diesel