Hello all. One month ago I bought a 1982 300D Turbo off a local used car lot, looking for a car I could (a) maintain myself and (b) eventually convert to run on waste vegetable oil. Body and interior immaculate, new Michelins. On test drive, noticed what I thought was "slipping" between 1-2 and 2-3 gears, but since the price was so good, thought I'd take a chance.

Began browsing the web, found DieselGiant, then Shopforum. Read extensively, bought about $100.00 worth of vacuum components, then began. And here's what happened.

With vacuum valve, checked Hg at brake booster, ~22" Hg, then checked components downstream. System would not hold vacuum. DieselGiant recommended checking master vacuum switch, found it to be good. Traced vacuum lines from master vacuum switch in driver door, found that at some point the yellow/red and yellow/green lines had been crossed, straightened that out. Found leaky actuators (driver's side rear door, trunk), replaced the former through Ebay ($25.00), latter removed and lines plugged. Pulled vacuum at master vacuum switch, all locks worked as advertised. Pulled vacuum at dual connector off principal vacuum line (one goes to master vacuum switch, other to vacuum reservoir), all locks worked. Cranked her up, door locks don't work. Test drove, transmission as before.

Came here. Found vacuum schematics (first BIG thank you), noticed valve in dash. Checked valve in dash after removing instrument panel, found valve installed backwards. Reversed valve. Checked vacuum at dual connector off principal vacuum line, door locks worked as advertised. Test drove, transmission as before.

Began serious work in engine compartment. Following DieselGiant, checked ALDA connections, found the lines to the ALDA switchover valve (on firewall next to brake booster) were disconnected from the valve and connected together. Reconnected to switchover valve. Removed and cleaned banjo bolt, reconnected. Test drove. Door locks worked as advertised (an indication of good system vacuum integrity), transmission as before.

Returned to engine compartment, read more on Shopforum, this thread, and discovered vacuum control valve (VCV). Tested vacuum, found it to be solid 14" Hg from the top connector. Test drove. Transmission as before. Went back to VCV, noticed for the first time that the rocker arm from the throttle linkage was disconnected from the metal lever on the back of the VCV. Which means my transmission was getting solid 14" Hg through all shifts (no wonder the "flaring," a more precise term, I have learned, than "slipping"). Reconnected rocker arm, which turned out to be frustrating because mine has a loose plastic clip to hold the rocker arm onto the metal lever on the VCV. Tested vacuum bleed from top connector, went smoothly (whew!) down from 14" to 0". Just for kicks, checked vacuum on line to transmission, found it to be solid. Test drove. No flares, though shifting was extremely soft (i.e., slight flare-like shifting between gears) and shifting occurred around 3200 RPM.

Following DieselGiant, replaced transmission vacuum valve levers (old ones were worn significantly), commonly referred to as 3/2 valves. Test drove. Still soft shifting and high RPM.

Came back, read more Shopforum. Learned about the control pressure cable (I believe it's referred to as a "Bowden" cable, obviously named so by a Florida State fan), adjusted it as per decription elsewhere here on Shopforum. Then read about vacuum adjustment on VCV. Removed plastic dome, adjusted nut (not screw) until vacuum ranged from 10" Hg down to 0". Test drove. NO NEED FOR A NEW TRANSMISSION. Shifting was extremely crisp (my tires tend to squawk a little between first and second, unless driving upgrade) and all gears shift dead-on 2300 RMP. And all of this with the EGR still connected.

Tonight, I adjusted VCV to 12" Hg initial vacuum to see if tomorrow the 1-2 shift is a little less harsh while not leading to minor flaring between 2-3. Again, big thanks to this forum, I do not need a new transmission.

Here's some learnings and questions I still have.

1. After all this, my cruise control began to work whereas it didn't before. Does the cruise control depend on a tight vacuum system?
2. Adjusting the control pressure cable: I tightened the cable to remove noticeable slack (right at the point of feeling resistance to the pull) at the point the metal connector was at rest, not against the metal stop between it and the cable bracket. The gap was around .15". Perhaps this is peculiar to my car, but by maintaining that at-rest gap I was able to fine tune shifts to current RPM.
3. One could, if one wanted an extreme exercise in frustration, adjust non-adjusting VCV by changing the height of the rocker arm connection to the throttle system. I imagine that would entail significant trial and error, since one would have to identify the exact point at which vacuum begins to bleed, then adjusting the rocker arm at-rest to connect the lever on the VCV at slightly before that point. Ugh. However, I'd bet that's what the designers intended, since different VCVs may begin to bleed off vacuum at different lever positions.
4. BTW, that flimsy plastic connector that ensures the rocker arm will stay on the lever on the VCV: I intend to replace it with a spring-lock, since the tip of the rocker arm has a groove around it. I was driving two days ago and the rocker arm slipped off - back to flaring between shifts.
5. Sam, regarding the orifice openings: I'm sure you're right, though I'm a newbie to MB's and am speaking as a rank amateur, that the orifices are fine tuning methods for delivering precise vacuum to the different components while ensuring that the brake booster always receives sufficient vacuum. That being said, I would not mess with them unless, for instance, I could not get sufficient vacuum at the VCV to reach my starting point of vacuum (formerly 14", then 10", now 12" Hg). I would love for a more physics-minded reader to give an description of how much a particular orifice size restricts vacuum, for instance, how much a .8 mm orifice restricts 22" Hg.

So, that's my story and I'm sticking to it. Again, huge thanks to this forum, particularly Brian and Sam. Though I still have some things to do (fuel low light always on, plastic door buffers in locking mechanism rotted), most are minor compared to my worries over the transmission.

__________________
Rev. Jeff Hayes
New owner, 1982 300D Turbo, 214,000 miles