Author Topic: Loss of Vacuum  (Read 218 times)

OLDGOLD

  • Enthusiast
  • *
  • Posts: 74
  • W116 Enthusiast
  • Location: Dallas, TX
Loss of Vacuum
« on: 04 August 2020, 10:20 AM »
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!

UTn_boy

  • W116 Addict
  • ****
  • Posts: 1,305
  • Chrome Bundts & bundts with white walls are a sin!
  • Location: knoxville, tn
Re: Loss of Vacuum
« Reply #1 on: 04 August 2020, 01:12 PM »
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.
1966 250se coupe`, black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3, papyrus white/dark red leather
1971 280sel Black/black leather
1973 300sel 4.5, silver blue metallic/blue leather
1976 280s astral silver/blue MB Tex

OLDGOLD

  • Enthusiast
  • *
  • Posts: 74
  • W116 Enthusiast
  • Location: Dallas, TX
Re: Loss of Vacuum
« Reply #2 on: 13 August 2020, 11:29 AM »
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!

UTn_boy

  • W116 Addict
  • ****
  • Posts: 1,305
  • Chrome Bundts & bundts with white walls are a sin!
  • Location: knoxville, tn
Re: Loss of Vacuum
« Reply #3 on: 14 August 2020, 04:54 AM »
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. 
1966 250se coupe`, black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3, papyrus white/dark red leather
1971 280sel Black/black leather
1973 300sel 4.5, silver blue metallic/blue leather
1976 280s astral silver/blue MB Tex

OLDGOLD

  • Enthusiast
  • *
  • Posts: 74
  • W116 Enthusiast
  • Location: Dallas, TX
Re: Loss of Vacuum
« Reply #4 on: 17 August 2020, 08:40 AM »
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.

UTn_boy

  • W116 Addict
  • ****
  • Posts: 1,305
  • Chrome Bundts & bundts with white walls are a sin!
  • Location: knoxville, tn
Re: Loss of Vacuum
« Reply #5 on: 17 August 2020, 12:02 PM »
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?
1966 250se coupe`, black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3, papyrus white/dark red leather
1971 280sel Black/black leather
1973 300sel 4.5, silver blue metallic/blue leather
1976 280s astral silver/blue MB Tex