It is a variable controlled leak/vent valve to reduce vacuum.

.

Roy - I was refering to the restrictive orifices in the picture attached.

Aren't these used to limit the vacuum or am I completely confused?

The small yellow one is pretty free-flowing.
The small white one and the small green one are pretty close with the green one slightly more restrictive, I think. They're real close.

Not sure what else I'm missing; perhaps the "dampfer" #72 in the vacuum diagram.

Right now, I have the big green damper between the main vac line and the IP. It does a good job of stabilizing the vacuum signal. It's a steady 13 between the damper and the VCV (M Pump) Since i don't have a switch over valve, do I put the smaller restrictors in line between the VCV and the modulator?

Brian Carlton Mentions "setting" his pressure to 8 but I'm not sure how he accomplished that. No matter what size restriction I put between the main line and the VCV, the reading is always the same.

On another note: I tried disconnecting all vacuum to the trans and it never shifted out of 1st gear. That doesn't seem right based upon what I've read.

Attached Thumbnails

 

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1981 300TD "The Green Lantern"
1980 300TD
1983 300D Euro "China Cat"

I switched around with the various orifices I found trying to get the vacuum at the modulator right. The orifices I have seem to make things worse, so, I have the green dashpot between the main line and the VCV to stabilize the signal, and no restrictive orifices between the VCV and the modulator. Vacuum at the modulator (at idle) is 13 in. hg. (30+ cm hg) and drops to zero upon applying quick throttle. Should it be 13 cm hg? THat could be a problem!

I then measured the modulating pressure at the right test port and had too much pressure there. With the engine running, I adjusted the modulator counter clockwise until the gauge showed 40.5 PSI (2.8). That was with the vacuum line disconnected but not blocked. When I re-attached the vacuum line, the pressure dropped below 2.8.

So, I think I have good vacuum at the modulator, the modulator is set at the right pressure and I cleaned and adjusted the VCV per Govert.

Current symptoms:
1. Almost an immediate 1-2 shift
2. 2-3 flare way worse than before
3. 3-4 flare

Interesting to note that now, when I'm in 4th and manually shift the lever to "S", 3rd gear engages and slows the car down. Before, it would just kind of coast along and not slow the car.

I guess my main question now is whether I'm supposed to be measuring the vacuum in inches or cm?

Thanks for your help!!!

__________________

1981 300TD "The Green Lantern"
1980 300TD
1983 300D Euro "China Cat"

You are supposed to measure the vacuum in bar ;-)

The vacuum at idle should be 0.35-0.4 bar vacuum, that is 10.3"-11.8" Hg. 13" Hg is a bit too high. You describe that the vacuum climbs up to 5" from 0, that is not good either.

I would suggest taking the VCV off the IP and clean it. After that, adjust the VCV until you get the desired vacuum level.

The problem is that you are missing the switchover valve, during coasting the vacuum should be full vacuum (approx. 22" Hg), that can influence the gear braking you are experiencing.

Govert - I removed the VCV and cleaned it out per your instructions and re-adjusted it with no change in results.

Should the vacuum drop to zero with any amount of throttle applied? Here's what happens:

If I hit the throttle quick, it drops to zero; doesn't need to be WOT
If I slowly apply throttle, (more like the way I drive) the vacuum barely drops at all, if any.
If I hit the throttle quick and hold it, the vacuum stays close to zero
If I hit the throttle quick and then gradually back off, it climbs back up to 13.

With orifices in place, I had 10"-11" of vacuum at the modulator with the modulator at 2.8 bar and got no 2-3 shift at all. I adjusted the VCV back and forth and not much change at all. WHen I removed the orifices, it would at least shif into 3rd.

The only way I can get the thing to shift even close to right is cranking the modulator in 4 turns from where I measured 2.8. Any restriction in vacuum before or after the VCV destroys the 2-3 shift.

It's time for a manual.

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1981 300TD "The Green Lantern"
1980 300TD
1983 300D Euro "China Cat"

The vacuum should respond immediately and linearly on the position of the accelerator pedal. At full load the vacuum should be 0.

The orifice is probably necessary to reduce the vacuum at idle a bit, it is in the diagram too (#17). The orifice prevents quick build up of vacuum after the VCV bled it off, so vacuum is reduced (to 10–11" as opposed to 13").

Modulation pressure should be read at 65 km/h (40 mph) without the vacuum line connected if I remember correctly. At idle, modulation pressure should be 6.8 bar ± 0.2 bar. That is only for the initial setting, pressure should be read at 65 km/h in D. From what I understand you have set the pressure at 2.8 bar at idle. That is way too low (>> flaring). See the table in post #8 by the Army.

If I have no vacuum attached to the modulator, it won't get out of first gear. I'd have a hard time going 40mph to test it.

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1981 300TD "The Green Lantern"
1980 300TD
1983 300D Euro "China Cat"

I had a look at the FSM. Modulation pressure should be read with the vacuum attached (as far as I can see, the FSM doesn't mention pulling the vacuum line, as with the 722.3 and 722.4 transmissions). So first measure the pressure at idle with the vacuum attached. Now we have a little problem, as you don't have a switchover valve. Vacuum will be too low at idle (around 10-13"). It is probably best if you make a vacuum line straight from the T piece to the modulator (for the adjustment at idle). With this set-up, adjust the modulator until you have 6.8 bar pressure (plusminus 0.2 bar).

Now disconnect the direct vacuum line and attach the line via the VCV. Go on the road, drive in D with half pedal, keep at 65 km/h with the brake. Read the modulator pressure, it should be exactly 2.8 bar.

Oh, and the rubber O-ring under the hood of the vacuum modulator can and must be replaced if it is loose. Otherwise it will not keep vacuum.

Sorry for letting this get 4 pages back! I've been out of town.

Govert - you are a wealth of information and I do appreciate your efforts.

That being said, I picked up a switchover valve at the pnp ($6) that appears to be in great shape. It functions properly and the little teflon thingy is in good shape.

I'll connect it up per the diagrams you sent and report back with the vacuum readings.

It may not be until Friday but I'll report as soon as I can.

Thanks again govert!

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1981 300TD "The Green Lantern"
1980 300TD
1983 300D Euro "China Cat"

Govert - I installed the switchover valve and it appears to be working.

At idle, the vacuum is 17 at the modulator and drops linearly with the throttle to zero at WOT.

I tried to adjust the modulator to 6.8 bar with the vacuum attached and it wouldn't go past 1.5 bar.

So, I unhooked the vacuum and tried to get 6.8 bar but it would not go past 4; no matter how many times I turned the modulator in.

So, I set the modulator at 2.8 bar at idle (because it will at least shift) and then adjusted in from there.

The 2-3 shift is the only real problem now. It still flares, however, with the switchover valve and the adjustments I've made so far, if I keep my foot in the pedal and ignore the high RPMs, it eventually shifts to 3rd in a normal, firm fashion without flaring.

What are the chances that I have 1. a bad modulator 2. a bad o-ring 3. a bad vcv, or 4. a bad K1 spring. The modulator holds vacuum so I'm tempted to rule that out.

Please let me know what you think!

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1981 300TD "The Green Lantern"
1980 300TD
1983 300D Euro "China Cat"

And have you measured the modulation pressure at 65 km/h (40 mph)?

The vacuum to the modulator should be around 22" at idle. Then, when the switchover valve is actuated, vacuum should drop instantly to around 10" (that is the VCV vacuum). When the accelerator pedal is pressed further, vacuum should drop to 0 at WOT. If the vacuum responds instantly and without fluctuation to movement of the accelerator pedal, the VCV is OK.

The plastic pin of the modulator can break, that can cause problems. Did you take the modulator out to check? Is the modulator red in colour?

I believe the 722.118 transmission doesn't have easily accessible K1 and K2 springs, but Army can tell you more about that.

I did measure it at 40 but I don't remember what it was. The gauge is still attached so I can let you know soon.

As far as 22" vacuum, it does go that high for a moment when I release WOT. The gauge goes from 0+- up to 22" and then settles in at 17 (it bounces).

I have not taken the modulator out.

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1981 300TD "The Green Lantern"
1980 300TD
1983 300D Euro "China Cat"

Govert - I checked the modulator pressure at 40 mph, in 4th gear, going up hill and it read 2.8 Bar. Perfect!

Also, I now have 23" vacuum at idle at the modulator. I plugged the vacuum line going to my headlight adjust switch and that bumped it right up to 23.

When I give enough throttle to activate the VCV, the vacuum only drops to 14 (as opposed to 10). I assume that the VCV is not dumping enough vacuum. Is this where the orifices come into play?

I have adjusted the VCV per your earlier instructions.

I think we're getting close!

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1981 300TD "The Green Lantern"
1980 300TD
1983 300D Euro "China Cat"