I need a little help diagnosing insufficient vacuum pressure. I am working on my 1984 300 TD (turbo wagon), it has about 235,000 miles on it.

It seems that my vacuum pressure is too low, erm, to high(?) ...it is not sucking hard enough. lol =)

I guess the first thing I need is the recommend procedure to test vacuum pressure, and what is the target number?

Thanks!
-Steve

__________________
1984 300TD wagon with heated dual-tank WVO.

What symptoms are you seeing? Brakes or shifting problems or door locks?

Where are you taking your measurement?

What is "too low"? I don't recall what the actual reading should be at the pump, but -12mm/Hg seems to come to mind. Don't quote me on that.

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )

Measure each vac barb on the main line while blocking off the other.

You're looking for ~21 inHg on one and perhaps ~15 inHg on the other.

And yes, what symptoms are you experiencing?

__________________
83 SD

84 CD

I think it might be insufficient vacuum because the brakes are a little hard to use, the locks are slow, and the engine is not turning off easily with the key.

I can manually shut off the engine by sucking through a vacuum hose.

I am interested in the testing procedure for vacuum pressure -- is it done with the small ports plugged or open? Should it be done connected or disconnected to the brake booster? If everything is removed and plugged, what should I expect to measure coming directly off the pump at idle speed?

Thanks!
-Steve

__________________
1984 300TD wagon with heated dual-tank WVO.

Do you have a MityVac? I'll bet that you have a leak somewhere. Usual suspects are the climate control and lock systems, but since you reported that the brakes are hard I would also check to make sure the main vacuum line isn't cracked. Even all the lines open on my car, I still have power brakes.

__________________
1984 300D
Euro spec, 5 speed
217,000 miles

Edit.

I commented before I saw the above information. I apparently posted the same time as Toomany MBZ, and missed his post. -- thanks for the numbers!

One of the tests I did yesterday was I disconnected EVERYTHING from the pump, plugged all the openings except for one, which I connected directly to the fuel shut off solenoid. It did not shut off the engine. Finger testing, it does not 'feel' like much vacuum is being produced.

I will measure the vacuum and post back what I find. Is there a rebuild kit available for these? Using the search function suggests that the bearing is a potential problem.


Thanks!
-Steve

__________________
1984 300TD wagon with heated dual-tank WVO.

Yes, a rebuild kit is available, search the 'net, but first try the buy parts button at the top of the page.

Pull the vac line going to the shut off actuator, it's brown/violet and goes under and behind the IP. Inspect for oil in that line, if you find some, you'll need a new actuator.

And we'll wait for the numbers.

__________________
83 SD

84 CD

21 inches of mercury is the reading at sea level. Lower readings are normal at higher altitudes. I see around 18 inches at a mile high.

__________________
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

In theory, there should be a 1" Hg drop in vacuum for every 1000' above sea level.