Would this be something like you are talking about? I am going to try and get one and fine tune my own if this is what you are talking about:
http://www3.towerhobbies.com/cgi-bin/WTI0095P?FVSEARCH=+OSMG7164&search=Go

Well, just for the record, Ive replaced that VCV which had a 'switch' like action.

I fitted the same type, (which isnt the 'usual' seen on US models) and have a fully proportional control of the Vac, right down to 0, so I guess the first one with the switch-like action must be faulty.

Shifts are much better and more predictable now, Before-they were either harsh or flary, neither which I liked much....

I think I may crack the faulty VCV open and take a look see as to whats gone wrong, and If it could be renovated....

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http://i190.photobucket.com/albums/z...0TDnoplate.jpg

Alastair AKA H.C.II South Wales, U.K. based member

W123, 1985 300TD Wagon, 256K,
-Most recent M.B. purchase, Cost-a-plenty, Gulps BioDiesel extravagantly, and I love it like an old dog.

W114, 1975 280E Custard Yellow,
-Great above decks needs chassis welding--Really will do it this year....

1982 MB 300 CDT 125K mi
Eng 617.952
Tranny 722.315
Cleaned intake banjo and line. Mostly blocked.
Also the switchover valve.
Replaced fingers and 135 dashpot.
Clean and lube rod ends.

Adjusted the VCV stop to 0.5 mm.
Required turning in the injection body stop
Adjusting the rod length was difficult as I couldn't make
the adjustment with the VCV in place. Remove,
adjust, check, remove ...
Tested vacuum lines for integrity and vac.
Adjusted VCV to 8 in vac for ok 1-2 shift and reduced 3-4 flare.
Piece of info I don't have is tranny hyd pressure.
Still working the problem. Car belongs to a friend.

1983 MB CDT, 125K miles, 722.315 tranny
The modulator was adjusted at 99k miles from 44 lbs to the correct 42 lbs.
Does anyone have experience of the effect on shift performance of:
1. Replacing the modulator.
2. Increasing modulator pressure slightly for higher mileage transmissions.
3. A combination new modulator and increasing pressure slightly.

What issues are your trying to resolve?

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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

This is a large thread. I am discovering the transmission vac control. The VCV is acting like a switch. There is no nice linear ramp of inverse inches of Hg v acc pedal position as I monitor line to the transmission modulator.

I pulled the VCV and opened it. 2 screws and the top comes off. There is a coil spring on the throttle input shaft which displaces a brass slug. There is a nut on a long sided nut. My question is can I adjust this to restore the linearity of control. Is there any data out there as to what the right performance curve (inverted In Hg V pedal depression %age) should be. If this has been discussed on here where is it at.

Any help much appreciated.

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Dionysius

I have a slight issue with my 87 190D and drive engagement. Going from either park or neutral to drive there is a hesitation. As soon as I go into drive there is a pause, then what feels like a slight engagement, slight pause then full engaement. Is that something that is controlled by vacuum?

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1987 190DT, clackity clack
90 Mustang track car
95 Lightning

Well, I DID crack open the one I had with a switch like action....

Inside, there is a spiral-spring that the throttle-shaft 'winds up. The outer end is attached to a diaphragm and a valve.
--The assembly was sticking, the spring was 'winding up' then suddenly the movement was transferred to the diaphragm...

Dismantling the whole thing, cleaning everything including the tiny metering orafice inside the diaphragm restored smooth operation and I was able to re-fit and set the VCV correctly. It has been working faultlessly since....

--I would not adjust anything, as we're not sure exactly what does what. Just dismantle the whole thing clean it all and make sure nothing is broken or sticking when the device is operated....

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http://i190.photobucket.com/albums/z...0TDnoplate.jpg

Alastair AKA H.C.II South Wales, U.K. based member

W123, 1985 300TD Wagon, 256K,
-Most recent M.B. purchase, Cost-a-plenty, Gulps BioDiesel extravagantly, and I love it like an old dog.

W114, 1975 280E Custard Yellow,
-Great above decks needs chassis welding--Really will do it this year....

Well after reading for two hours and thinking in the middle I could probably just install my 240D's standard faster than I could get through this thread

I pushed through ! This resulted in a wealth of info. If you start at the end or the middle the full effect of it will not be realized.

The 81 300SD I just transplanted the 83' motor into would break your neck and chirp the tires when shifting through the gears. Thus I found this thread.

The new engine had a brand new VCV valve on it nothing wrong with that right ??? Wrong !!!!

I removed the EGR valves ..... no difference
Changed the green dash pot......... no difference
Checked for bleed down on the modulator........it Held vacuum
Changed the new VCV valve for the old ugly one (original to the 81's trans ).............. OH WHAT A FEELING !!!!!!!
Who ever installed it "adjusted " it . Vise grip marks on adjuster screw!! There's your theory of just a little adjustment is possible Brian. Spring was tweaked and never shut down the bleed valve

May be what killed the trans in the 83' ???


The car shifts better than my 2003 4runner !!!!!

On a side note I did not find one orifice fitting on any vacuum line on this car. All vacuum systems work flawless.
Therefore I agree with Brian as for the tuning of the VCV valve being the Key here . Even the original Steve Brotherton paper states Mercedes went through numerous changes. They finally settled on the amplifier "to reduce the sensitivity of the final signal to small changes in the proportional signal ". ( VCV valve is the proportional control )

I wonder if the newer 85' system can be incorporated into the older cars ? Cost effectively ? If not keep tuning !!!

Thanks to all who contributed to this thread ! Thanks Brian for sticking with this thread I appreciate the time and energy it took ! Also for passing on the knowledge to those of us new to Mercedes autos.

The wife says a big thanks as well !!!! ( its her car )

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Experience : what you receive 3 seconds after you really needed it !!



86 300SDL 387,000? Motor committed suicide
81 300SD 214,000 "new" 132,000 motor
83 300SD 212,000 parts car
83 300SD 147,000

91 F700 5.9 cummins 5spd eaton 298,000
66 AMC rambler American 2dr auto 108,000
95 Chevy 3/4 ton auto 160,000
03 Toyota 4runner 180,000 wifes

I bought a 1981 300D at very low cost which had a massively flaring transmission. This was my first venture into this type of problem. I carefully studied this thread plus read and read for some four plus weeks. Great info on here.

Here is where I am at. Removed the 3/2-valve and rerouted the plumbing. This did have a leak. It is a useless appendix on this car never to be recalled. Tested diaphragm on modulator valve on transmission. It is holding indefinitely so appeared fine. I have a MityVac. Next I removed the VCV and opened it. I understand its function.....it emulates the vacuum of a gas engine by controlled vacuum leak in proportion to pedal position. This was set incorrectly. It had a totally non-linear response. I cleaned it ,and calibrated it and I got a fine curve with 8 in Hg at idle and 0 in Hg at WOT. The system has two orifices, black at main vac source and yellow further on. All looks fine and original. Trans was now no longer flaring but I could discern 2 things that were not right. The 1-2 shift was too harsh and there was a stacked 2-3 3-4 shifting and it was downshifting too much. I disconnected the elec cable at foot of pedal. No difference. Next I tooled up and placed a 150 psi meter on the tranny test port, plugged the vacuum, started engine and voila.....the meter pegged. Next I extended the T handle on the mod valve and cranked it out. No change was happening to pressure until almost at the end and pressure went very jittery and was still up at 120 in Hg. Way too high. My trans is a 722.118 and it is supposed to read 3.0 Bar or 43.5 psi. Next I removed the modulator valve which is red and I believe the replacement part should be 1232700679 from my web research. I brought it to my kitchen table to study it. Based on what I see it is reacting when I suck on it by retracting the pin which is obviously attached to the diaphragm. The external condition looks like new. No rust or damage visible.

Why can I not adjust my pressure down to 43.5 psi??? Is it a calibration issue due to a spring in this valve having gone way out of spec??? If I purchase a new modulator valve will it make things work??? Is there some other problem possible and if so what is it?? The trans fluid is pristine....the color of a good rose wine when placed on a kleenex and pas de burnt odor. Also the valve pictured for replacement does not have the pin assembly on it. Is this a transferrable piece??

Please help me if you can and I will be tojours grateful........

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Dionysius

Does that vehicle have a Bowden cable?

Brian,

I do not believe it has. I am not 100% sure what it is....is it a mechanical linkage to the tranny?? If so I do not believe it has. Is there a check I can make for you??

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Dionysius

This is a bit critical to determine.

You must determine if it has a cable from the throttle linkage down to the transmission. If it doesn't.........the vacuum levels remain absolutely critical for both the timing and the duration of the shifts. Removing those 3-2 valves may not have been the best solution in that case.

No it does not. The throttle does move the VCV valve on the rear of the IP and that is it.

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Dionysius

Then, vacuum plays the entire role in the quality and timing of the shifts. If they are not flaring, I'd increase the vacuum level from the VCV.