hello all. I got this strange vacuum issue that I thought I had tackled, but is non the less still there.

83 240d

80% of the time, vacuum works great: shifts great, brakes fine, turns off fine. The rest of the time, high rev shifts, no brakes, won't turn off... Sometimes I'll pull off the road, shut it down, and when I start it back up, everything is fine. Other times I'll just keep driving and deal with the high shifts and then Poof everything comes back and works rosy.

So, today I finally go around to removing all the EGR stuff, thinking that must be it. Nope, still there. I hooked up my mightyvac to the line coming right off the pump and no leaks. I hooked up to the VCV, and got no leaks and higher vac pressure bled off and then held. Vac res tank holds pressure no problem, either.

Also, I blocked off the locks so they are not in the system either.

Any ideas?

Thanks! kat

I've owned my 85 TD for about 6 years and it's done the same thing about 4 or 5 times in those years. I'm thinking it must be a stuck check valve in the vacuum pump or something like that. Everytime it has happened to me I've shut the car off with the manual lever and the next time I drive it everything has been back to normal.
Complete loss of vacuum like that can't just be a minor leak somewhere. It has to be either a problem at the pump or at the brake booster which can dump huge amounts of vacuum quickly.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Is this problem related to the length of time the engine has been running? => heat related?

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

The check valve in the nipple where the hard line attaches to the vacuum pump has failed. The parts fall out and intermittently block the intake port.

http://catalog.peachparts.com/ShopByVehicle.epc?q=&yearid=1983@@1983&makeid=63@@MERCEDES+BENZ@@X&modelid=6143%3AED%7C10000129%3AMBC%7C1489@@240D&catid=240706@@Diesel+Injection&subcatid=240735@@Vacuum+Pump+Check+Valve&applicationid=W0133-1620263@@Vacuum%20Pump%20Check%20Valve&mode=PA

@Army - doesn't matter how long it's been running.

tangofox007 - Thank you. Is there a cheaper fix? lol.

You can fish the broken parts out of the inlet for free.

lol.

I had some intermitten vac issues in my 78 240D, and it turned out to be the vac pump. It would loose all vac when I applied the brakes firmly a few times in a row. I swapped in another one I had and the issue when away. So I think you are on the right track with the vac pump. I'd look into rebuilding the vac pump along with the other suggestions here.

__________________

Here is the piece that I fished out. It's not needed in there? Thanks.

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That part should retain the valve plunger and spring in the nipple. If it had fallen out, the plunger and spring need to be accounted for.

Crap. And, since it's a vac, it probably sucked that stuff down into the pump?

In my experience, the parts won't make it past the intake port. Worst case, you might have to remove the pump and dump the parts out.

Wow Tangofox...you were right on the money with that diagnosis!

__________________
1987 300TD
1984 300D
755,000 KM and going strong
BC Canada

Winner! Duh!

A few more questions on this, please:
1: if the two little pieces remaining in the vac system fell into the pump, can I just remove the cover (with the slotted screws) on the pump facing the fan to get at them? if so, do I need a new gasket after removal?

2: now that I've removed the EGR stuff, I think I'm making too much vacuum (20" at idle) and have very harsh, high RPM shifts. How do I moderate that?

3: lastly, does this on the VCV need to be connected to something (pic)?

Thanks!

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