84 300sd. I can’t seem to get the vacuum sorted out. Shifts aren’t quite right and I have intermittent trouble shutting off. Ive been through every connection and cleaned or replaced anything that was even half suspect including checking the connections to the ignition and that whatzamagig climate control thing under the driver side dash.
It also seems unusually sensitive to kickdown cable adjustments. A couple rotations either way and it behaves very differently.
To help diagnose where my problem I bypassed the “vacuum switchover valve” on top of the valve cover I did this by simply eliminating each T that sent a vacuum line to it and back from it from the area near the injection pump . The EGR had already been blocked off by a metal gasket but all vacuum lines to it remain. (testing purposes only of course)
Does that black box on the top of the valve cover only serve to control the EGR, or does it play a role in shifting and other vacuum functions? If it is there only to control the EGR did I bypass it correctly by just straight lining any lines that were going to it? Or, should I T together the vacuum lines that used to go to that box?

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84 300SD 274K
38K miles on flatplate heat exchanger and various diesel/veg blends. prior to that 4K miles on unheated veggie blends with kero and DinoD.

First you need a Mity vac to test the systems. Just because the connection to the vacuum lines seem OK does not mean the actual component is not leaking. The only way to verify this is with a mityvac.

One of the air switches on the top of the valve cover does effect transmission shifting. The other is for the EGR valve.

The vacuum system is quite extensive.
Your AC system has Air switches behind the Ac controls. Vacuum lines and connections to each element. 5 vacuum elements in the dash.
Your door lock unit has 1 main control valve and 5 elements as well as a pump.
Your engine area has numerous vacuum units including the modulator valve at the transmission.
So check all the lines, connections and units with the mity vac. Isolate the AC vacuum lines by using golf tee's in those lines while trying to work the engine lines. some thing with the engine shutoff brown lines. If it still acts up then you'll know its an engine problem and not the Ac or shutoff.
Be meticulous with the checks. You checking vacuum and a small leak can effect the transmission shift. If all these check out OK then there are other transmission shifting adjustments. The Vacuum control valve on the injection pump, the modulator valve in the transmission, the air switches in the engine compartment, the air valve on the valve cover and the metering valve where the brake booster line is bled off for the transmission.

Dave

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1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car

of course very familiar with mighyvac.
Uh oh then but that is kind of good news and means that I just have to replace those lines and I should be good to go.
Now, what lines go where? I took a pic with my camera phone before I took it apart but the pic is pretty inadequate.
Ive attached a pic from one of my vacuum repair bookmarks. The schematic is for a 123 but it suggests my lines were not plugged into the right holes in the switch on the VC anyway. My lines were plugged into the bottom right two holes as you view from the front instead of top and bottom right.
Is this right?

Attached Thumbnails

 

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84 300SD 274K
38K miles on flatplate heat exchanger and various diesel/veg blends. prior to that 4K miles on unheated veggie blends with kero and DinoD.

You do not have to replace those lines. All the lines to and from the black box can be eliminated. Follow them back to the T's and remove the T. Connect the two remaining lines that were at the T with a short section of hose.

Dave, on all SD's from '81-'85, the two vacuum switches on the top of the valve cover serve to operate the EGR exclusively.

They have no direct operation or effect on the transmission shifting.

I've recommended to everyone who has these engines to remove all the Tecalan lines that lead to and from the black box.

One line is the supply vacuum.........one line is the vent.........and the third line leads to the thermo vacuum valve in the thermostat housing and then onto the EGR valve.

These switches frequently leak and have an undesirable effect on transmission shifting however, they have no direct function reagarding control of transmission vacuum.

Please realize that older engines, prior to 1981, will likely have a different configuration.

Thanks for the info.

Dave

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1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car

is that also true of the 83 300TD?

Yes, the '83 W123 with the 617 had the same configuration.

The tranny should shift hard all the time with no vacuum, and take longer to upshift. Like Brian says, do not worry about it. It is completely normal. Brian is one of the MB encyclopedias here. You will learn a lot from him, Larry Bible, and Sam, Mr Safety.

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

99 W210 E300 Turbo Diesel, chipped, DPF/Converter Delete. Still needs EGR Delete, 232K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Gone and still missed...1982 w123 300D, 1991 w124 300D

I discovered that the "modulator valve" cap was in crummy shape. I hadn't given this any attention before. I went on a old thread archive search blitzkrieg.
Should I stay way away from any adjustment on the modulator, or will turning a notch clockwise buy me more time for a part that may be on its way out?

I dont quite understand your tips in your last post regarding testing under 'no vacuum' conditions. I tried doing a straight through connection of the lines that T down to the vacuum control valve and covered the T above the damper with my fingers and the engine would not shut off on its own.

Im encouraged by finding the cracked modulator cap. Perhaps a fresh cap and a damper from the local stealership and I may be able to shut off without popping the hood.

I could not find the vacuum control valve at fastlane. Does it go by other names?

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84 300SD 274K
38K miles on flatplate heat exchanger and various diesel/veg blends. prior to that 4K miles on unheated veggie blends with kero and DinoD.

I'd like to isolate the VCV and the modulator from the vacuum system. Therefore, please plug the supply line as directed above and drive the vehicle. If the vacuum problem is eliminated and you maintain brakes, then the VCV might be considered the culprit. If the brakes are lost and the engine still won't shutdown, then you've got more problems than the modulator and the VCV.

Here's the valve.........a bit costly, however.

http://catalog.eautopartscatalog.com/mercedesshop/sophio/quote.jsp?clientid=catalog.mercedesshop&cookieid=1XL0VHEI02071C4AAG&baseurl=http://catalog.peachparts.com/&partner=mercedesshop&year=1984&product=D2032-15990&application=000004527

What happens if you bypass the VCV? The reason I am asking is because I think I may have a vacuum leak somewhere. I am registering only 4.4-5 hg with the VCV and the transmission is shifting hard. Directly hooked up to the vacuum pump I am getting about 24 hg. With VCV bypassed and a direct shot to the trans modulator I am registering about 9 hg. It shifts very nicely now. I think I want to keep it this way until I figure out what is leaking. Would it hurt anything?

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CJ

1983 300D 12X,XXX

Looks like intermittent shut off prob is solved for now. I was checking some vac measurements again. On the the valve up by the brake booster I disconnected different lines and measured vac. Both nipples before the white valve measured about 12-15hg.
There are two nipples on that white valve. One goes to the VCV and modulator, and the other goes to lines going back into the cabin.
I stumbled onto that when I switched the lines on the two nipples that it would turn off on demand consistantly and instantly instead of only turning off 40% of the time.
Why this works I don't know cuz both holes have the same amount of vacuum measured at idle. They also have the same amount of vacuum if you pull the lines first, start it, turn ignition off, and measure with ignition off and engine running.

Trans shifts seem reasonable. I am getting a measurement of 15hg on the main line coming off the pump. Is this adequate? Some step by step guides say 15-20, others say to troubleshoot the pump if you are not getting 21+ here.

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84 300SD 274K
38K miles on flatplate heat exchanger and various diesel/veg blends. prior to that 4K miles on unheated veggie blends with kero and DinoD.

Hello list,

Brian Carlton made a statement here as follows............. On all SD's from '81-'85, the two vacuum switches on the top of the valve cover serve to operate the EGR exclusively.

They have no direct operation or effect on the transmission shifting.

I've recommended to everyone who has these engines to remove all the Tecalan lines that lead to and from the black box.

One line is the supply vacuum.........one line is the vent.........and the third line leads to the thermo vacuum valve in the thermostat housing and then onto the EGR valve.

These switches frequently leak and have an undesirable effect on transmission shifting however, they have no direct function reagarding control of transmission vacuum.

Well when I short out my black box, two Tecalan leads, in and out, shorted with a tube!
The 1st gear on down shift, gives a big clunk
I already have the EGR plugged!

I have just got my tranmsssion working quite well now, changes up through all the gears nicely

Any thoughts on this appreciated.

Brian