vaccuum, weird problem? - PeachParts Mercedes-Benz Forum

mailmanmike · #1 08-11-2003, 10:13 PM

Hi all, I searched this forum for an answer, but I'm not sure I found it, so:
83 300d turbo, 230,000 miles.
Suddenly one day, engine wouldn't shut off without depressing locks on door.
Then, suddenly, a month later,engine won't shut off AND no power brakes.
Car sits overnight, starts, power brakes come back.
After car gets warmed up and re-started, brakes and shutoff go out again.
Am I more than likely looking at a vaccuum pump?
If so, is it common for them to intermittently go bad?
Thanks in advance.

adamb · #2 08-11-2003, 10:45 PM

When I initially got my 1985 300D 2 years and 45k miles ago, I had the same problems. I traced them to be caused by several connectors and three of the five vacuum servos behind the dash panel which I have perfected the skill of replacing in record time (3 minutes - I timed myself) These servos cost about 35 each and are another common thing.
Without knowing the history of the car, I would start by making a general assessment of all the vacuum connectors in the engine compartment. Try to see if they are brittle or porous looking with little cracks in them or swollen at the end where they connect to whatever it is. Also, take a look at the main vacuum supply line going to the brake booster and clean out any ports near the booster on this tube as they often will clog. You can use a needle to get in the small orifice.
Put a vacuum guage in many areas throughout the system, especially at this main line and ensure you get about 15-20 psi vacuum. Pumps are cheap to rebuild - about 40 bucks - it might even be one of the ports/ valves in the pump that you could simply clean. I "biffed" my plunger shaft in the pump when rebulding mine, so be careful when tightening this nut that holds the pump piston in place if you rebuild. I bought a new one and it cost in the area of 170 or so.
Sometimes the vacuum system will decide to be lazy based on the perfect alignment of the stars. But really, the heat and temp extremes in this summers weather can cause things in the vacuum system not in top condition to work intermitantly.
Have fun with it,
Adam Bush

mailmanmike · #3 08-12-2003, 01:33 AM

Ah. Thanks for your response.
I have done a visual connector check, under the hood, seems to be OK.
One thing you mention is the servos under the dash, my two center vents quit working some time ago... (forgot to mention that) so I'm sure they need replaced as well?
I will go over your items and check all those... by the way, in 'fastlane' they list two different vac pump rebuild kits...
I wonder which I need?
Again, thanks!

Rick Miley · #4 08-12-2003, 11:16 AM

Don't go into rebuilding that vacuum pump until you're sure you need it. The best thing to do is go down to AutoZone and get a MityVac for about $26. It has a vacuum gauge on it that you can use to test the system. There's a port on the main vacuum line to the brake booster that supplies vacuum to the rest of the accessories (A/C, door locks, shutoff). If the vacuum is fine at that point, then your problem is an accessory leak. If not, then it is the vacuum pump, main line, or brake booster leaking.

Diagnose before you start changing parts.

Stevo · #5 08-12-2003, 04:55 PM

Rick is right on...these cars should come with a Mitty Vac along side the jack there in the trunk. If your gona be around these cars might as well buy a Mitt Vac but I would spend a little more and get the metal one. Harbor freight has them. A leak the size of yours should be easy to find. Good luck

mailmanmike · #6 09-24-2003, 09:27 PM

Update, the problem did not fix itself.
Bought miti-vac, nice tool, disconnected main vac line from brake booster, only get about 4-5 in of vaccuum there.
I think I need a vac pump rebuild, right?

Rick Miley · #7 09-25-2003, 09:01 AM

Well, the only things left are the line and the pump. If you're sure the line is not leaking, then it's time to dig into the pump.

wheelguru · #8 09-26-2003, 10:48 AM

I had a leaky shut-off mechanism and bad brake booster, replaced them both, now I am down to just a leak somewhere in either the trunk latch mechanism or fuel door lock. It is nice to be able to turn the car off from inside and have power assisted brakes again.

mailmanmike · #9 09-27-2003, 10:03 AM

OK now, I got a vac pump rebuild kit from FastLane (a great way to get parts, by the way)
And did the rebuild yesterday...
It seems to have solved the power brake problem!!!
Now I need to chase down the leak which is causing it to not shut off except when the doors are locked.
Thanks to all you good folks for your help!!