Author Topic: Vacuum leak  (Read 172 times)

John H

  • Newbie
  • Posts: 8
  • W116 Enthusiast
  • Location: West Yorkshire, UK
Vacuum leak
« on: 29 October 2020, 07:02 AM »
Hi

My newly acquired 450SEL central locking system is working, but slow. After running the engine, if the car is left a couple of hours the locking system still works, but after standing over night it doesn't.

I'm thinking this points to a small vacuum leak? (Any other suggestions are very welcome.)

I haven't started looking for a leak yet, but there are no other obvious symptoms of vacuum leak. It idles and runs fine, brake servo works even if the car has been parked a while.

If it is a leak, I guess it could be anywhere, but given my symptoms are there any likely points in the system I should check first?

Thanks, John




rumb

  • W116 Addict
  • ****
  • Posts: 1,602
  • MB Enthusiast
  • Location: Fort Collins, Colorado
Re: Vacuum leak
« Reply #1 on: 29 October 2020, 07:20 AM »
John, I'm sure there are post already out there.

One would basically work their way thru the system checking with a a mitivac starting at the lines/blue check valves by the fuse box and then next the drivers door vac switch. Then go to each door, gas lid and trunk actuators and test them. One can also test the vac tank in the front fender and trunk - the little grommets there get hard.

'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

John H

  • Newbie
  • Posts: 8
  • W116 Enthusiast
  • Location: West Yorkshire, UK
Re: Vacuum leak
« Reply #2 on: 29 October 2020, 10:37 AM »
Great, thanks

raueda1

  • Vintage
  • ***
  • Posts: 644
  • Assimilated. Resistance is futile.
  • Location: Salt Lake City, Utah
Re: Vacuum leak
« Reply #3 on: 29 October 2020, 12:09 PM »
John, I'm sure there are post already out there.

One would basically work their way thru the system checking with a a mitivac starting at the lines/blue check valves by the fuse box and then next the drivers door vac switch. Then go to each door, gas lid and trunk actuators and test them. One can also test the vac tank in the front fender and trunk - the little grommets there get hard.
I got the same problem, so will follow this closely.  I dread it though.  What exactly is a mitivac?  Seems to be a common term for various devices.  Thanks,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

daantjie

  • W116 Addict
  • ****
  • Posts: 2,093
  • W116 Enthusiast
  • Location: Vancouver, BC, Canada
Re: Vacuum leak
« Reply #4 on: 29 October 2020, 01:46 PM »
John, I'm sure there are post already out there.

One would basically work their way thru the system checking with a a mitivac starting at the lines/blue check valves by the fuse box and then next the drivers door vac switch. Then go to each door, gas lid and trunk actuators and test them. One can also test the vac tank in the front fender and trunk - the little grommets there get hard.
I got the same problem, so will follow this closely.  I dread it though.  What exactly is a mitivac?  Seems to be a common term for various devices.  Thanks,

Vacuum hand pump, a must have to chase vacuum loss gremlins:

https://www.amazon.com/Mityvac-MITMV8500-Silverline-Automotive-Vacuum/dp/B0002SQYUA



Daniel
1977 450 SEL 6.9 - Astralsilber

rumb

  • W116 Addict
  • ****
  • Posts: 1,602
  • MB Enthusiast
  • Location: Fort Collins, Colorado
Re: Vacuum leak
« Reply #5 on: 29 October 2020, 01:59 PM »
While time consuming, it is a great way to get to know your car. Removing door cards is not all that difficult, just remember to lift up gently after popping the bottom clips so you don't break the plastic hooks. The online manual shows how. While in the door you can inspect and lubricate the window tracks and if inclined remove outside door handles and lubricate. Simple and will make the handles so very easy to open.mb lock lubricant is excellent in making your key turn easily.
Vac leaks are often the actuator rubbers. Someone sells new rubbers or you can buy used units for about $30.
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

John H

  • Newbie
  • Posts: 8
  • W116 Enthusiast
  • Location: West Yorkshire, UK
Re: Vacuum leak
« Reply #6 on: 30 October 2020, 01:56 AM »
Thanks for the advice.

I am going to delay this slightly. I think my car needs new injector seals, so I'll change those first, in case that is causing my slow loss of vacuum.

I will update on progress