Hello gents! I was driving my 1980 300SD yesterday and the A/C fan wouldn't turn on, then I noticed that the door lock pins weren't raising as they would 10 seconds or so after starting the engine. Then I felt the transmission starting to kick like a mule especially at low speeds. So, it would seem that I have lost vacuum somehow. The good news is that the engine shuts off immediately so I know the vacuum for the shutoff-valve is still good thank God!
Anyways, I inspected under the hood and don't see any loose or damaged vacuum lines, so I suspect the vacuum pump has finally bit the dust. Is there anything else I can check to verify this? Thank you for your valuable help!
P.S. the vehicle itself drives great except for the hard shifting, and the transmission kick-down works very well and I haven't tinkered with anything under the hood in the last few months so I didn't knock something loose or anything like that. Thanks again!
If you still have power brake assist then the vacuum pump shouldn't be suspect. I'd be more worried about a vacuum leak in one of the door lock actuators and/or in one of the climate control vacuum actuators.
After speaking with my mechanic it turns out that he actually put a check-valve in the vacuum line going to the brakes so that if I did lose vacuum that I wouldn't lose the brake assist. Now that's a good mechanic!
I did some inspecting again this morning and I did find that One of the the x-fittings had split causing the leak. Got a new one and now everything works. Guess I should've looked harder and I wouldn't have had to drive 25 miles to work in the Texas heat for the past 2 weeks with engine heat coming out of the defroster lol. Live and learn!
Why was a check valve installed? There's already a check valve in the vacuum pump itself. Also, if the vacuum pump quits working a check valve won't serve any purpose at all.
He told me he installed a check valve so if I lose vacuum to the doors, ACC, Trans that I won't lose the brake assist.
Well, again, the car came with check valves from the factory for this reason. They're beside of the brake booster. Why was an additional one installed?