My '87 300td started to shift a bit too firm. I checked the line going to the modulator and it reads only around 8 at idle.Expected more like 15. Where to look next? Appreciate any comments.

Be good to start by confirming the output of your pump.

If its good, start checking for cracked and leaking lines to include
the fittings.

__________________
1985 300D 198K sold
1982 300D 202K
1989 300E 125K
1992 940T

"If you dont have time to do it safely, you dont have time to do it"

"The democracy will cease to exist when you take away from those who are willing to work and give to those who would not."

The old style pump is known for failure and should be updated to avoid it falling apart...the updated version has screws on the outside of face (toward radiator), while the old style/original vacuum pump had a smooth face with no screws. Which do you have?

Also, how much vacuum are you getting elsewhere?

__________________
1987 300TDT - 195,000 (Original #14 head)
1993 190E 2.3 - 105,000
1981 300D - 250,000

Check the vacuum level at the input to the VCV (one of the two lines that enter the top of the VCV).

This will confirm whether you've got a vacuum leak elsewhere in the system (highly likely).

If you haven't already done so, all the vacuum components on the right side of the vehicle and be disconnected and the four way that's at the output of the vacuum pump can be changed to a two way (F) connector.

OK - will go to the source. I have the "new" design vacuum pump I installed sometime last year. And I have dumped all the stuff on the right side of the vehicle as recommended (2-way connector from the main supply). Will keep you posted.

OK- checked the vacuum going into the transducer at 22, pulled the vacuum on the transducer:holds, pulled the vacuum on the modulator:holds. Vacuum at the nipple for the line to the modulator:8. Is it the way it is supposed to be?

The question is:

What is the vacuum that is going into the VCV?

And, what is the vacuum output from the VCV to the transducer?

Is the nipple partially blocked?

__________________
Charles
1983 300D, bought new, 215k+ miles, donated to Purple Hearts veterans charity but I have parts for sale: http://www.peachparts.com/shopforum/mercedes-benz-cars-sale/296386-fs-1-owner-83-mb-300d-turbo-rebuild-parts.html

Around 22 in. vacuum in, 8 in to transmission. I took the transducer out and pulled the vacuum on it with everything intact except the line to the transmission(blocked) and the vacuum in( mitty vac). I could feel some kind of gizmo inside making a little whirrling noise when I pumped. Maybe some kind of membrane inside busted?

Doesn't answer the question.

What's the vacuum level going out of the VCV?

Wait, I am confused: is it not the line coming from the VCV that goes into the port marked "VAC" that I reported as receiving 22 in,? And the line marked "TRA" that outputs the vacuum to the transmission via the modulator?

I'd like the vacuum in the line from the VCV to the transducer (blue flying saucer). IIRC, the port marked "VAC" has full vacuum applied..........not the modulated vacuum that I'm interested in.

This value needs to be observed while driving the vehicle to determine if the VCV is working correctly. As the rack is opened, the value should fall relatively proportionally to the position of the pedal.

I'd T in the Mity Vac or vacuum gauge into the transmission modulator line, run the hose out of cowl, rest the gauge on the windshield so it is visible and go for a drive to monitor it's performance.

__________________
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

So, it is the line that goes into the bottom part of the transducer that I need to take the measurement at? Before it gets there, there is some kind of switchover valve that the line from VCV feeds into.
Also, should I not have the 12-15 range coming out of the transducer ,at idle, to the transmission regardless?
At this point I'd like to understand how are the vacuum lines supposed to arranged between the VCV and the transducer(blue soucer thingy).

There is only one line from the VCV to the transducer. That line will be interrupted by the switchover valve (used for cold starts), but won't affect your results once the engine is warm.

You should have 12-15 at idle going to the modulator, however, since you don't have it, we're trying to determine where the problem lies...........but, without your capability of making this test, we can't accomplish that.