Vacuum issues
 

Hello, lurker of some time and mechanical innocent living in Ottawa at your service.

My car is an '82 300D turbodiesel with ye olde issue of running on with the ignition switch in the off position. The shutoff valve recieves at least partial vacuum since it succeeds in dogging down the motor at least slightly most days.
Anyway, I've got the Hayne's manual next to me which is more or less mum on this question, and a dozen or so threads on this particular forum as well as some excerpts from the mercedes CD manual pertaining to the subject open to me, and I've surmised that my vacuum system probably has a few leaks in it (centre vents, door locks not functioning, A/C working intermittently), but despite that I figure it's probably a torn diaphragm in the shutoff component in the IP.
Firstly, can I humbly ask you guys to confirm this? There's a heavy residue of oil on the Y junction coming out of the side of the shutoff valve as well as a lesser amount on one of the Y junctions branching out from the top end of it. From what I understand, that oil can originate from the vacuum pump itself being faulty or the shutoff valve. I would like to optimistically say that the problem lies with the shutoff valve as it would necessitate a relatively cheap and easy repair, but maybe oil from there goes in the brown lines leading to the cabin and not the Y junctions I've mentioned? Or I suppose it's possible that it's both the pump and the valve and too great a magnitude of vacuum leakage.
Adding to my suspicions is the fact that my brakes, while working more or less well, are sort of mushy and tend to respond more quickly when pumped. I'm not losing fluid and thus my lines are okay; does this mean my vacuum assist is wonky or is this the way the brakes behave when the pads get thin?

Three more questions:
The shutoff valve is probably really old so I'll probably replace it anyway. How do I do this? The anatomy of the bloody thing is more or less a mystery to me and I have no knowledge of possible caveats or tricks to getting it off. I see two female hex bolts that look like they retain it to the IP. Do I just unfasten those and pull it out?
I mentioned earlier that my centre vents are out of order, and I've located a black hose hanging free under the dash that looks like it supplies it with vacuum. Where's the nipple that it mates to?
Finally, can I get my hands on the mercedes CD manual from anyone around here, possibly through PM? The dealer wants my soul for anything I ask them for.

Thanks in advance!

Welcome to the forum.

The first thing to do is to get a Mityvac so that you can test various points in the system.

Connect the Mityvac to the shutoff valve and pump it up. If the engine shuts down, that's not the problem.

Use the Mityvac to read the vacuum from the main supply line coming from the vacuum pump. Anything over 20" is fine.

Do not attempt to change the shutoff valve without thoroughly understanding the risks associated with this endeavor. If you do it wrong, and it's very easy to do it wrong, the engine runs away and it destroys itself in less than 30 seconds. You need to be prepared to shutdown it's air intake in less than 5 seconds if this happens.

I had the same symptoms with or 116 model diesel. The first place to check is the vacuum pump. No matter where other leaks are, if the pump is leaking fixing all the other leaks won't solve the problem.

Buy a MityVac vacuum tester; should be about $25. Disconnect the main line from the pump to the brake booster at the brake booster. Plug off any lines teeing off this line (golf tees work), connect the MityVac at the brake booster fitting and pump vaccum. The vacuum should both pump to over 15 psi and hold there for quite some time. If it doesn't pump up and stay, you need to rebuild the pump, which is not all that daunting. After rebuilding, then you can either have a working vacuum system or be able to troubleshoot the rest of the system.

Jim W.