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#1
06-22-2008, 12:36 PM
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W124 VCV - 20inHG in, 9niHG out - OK?
The vacuum control valve seems to be cause of my car changing gears very 'crisply' (to put it mildly). THe FSM says it should have 12inHG (420mBar) at the output, and about 20inHG (700mBar) at the input.
Well, it has the correct input 20inHG, but is only showing 9inHG at the output with the throttle at idle. And by 1/4 throttle, it is at 0inHG. So the tranny changes very crisply, as noted. There are no leaks at the tranny, and the rest of the stuff seems to be doing fine. Anybody know if it is serviceable? Or if I am wrong in deducing it is the problem? When I move it all the way to the back (ie soft shifts) the car does shift very softly and smoothly. But a little too soft. It looks like the top of the VCV can come off, but I dont know what to look for if I do take it off, or if there is anything to be done. Its $110 for a new one, so I want to be reasonably sure it is the problem first. Thanks.
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1983 240D Silver/Blue "Sadie", unknown miles. 100k miles on WVO single tank, converted to 2 tank about 10k miles ago, FPHE, Injector Heaters, Aux Fuel pump. Alcohol/Water injection. Frantz oil bypass filter 1992 300D 2.5 Turbo Green/Tan "Jade" 267K miles Stock. 1992 300D 2.5 tan/tan "Rocky" on 2 tank WVO. Pressure actuated Turbo "rat's nest" surgery completed. 197k miles 
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#2
06-22-2008, 03:56 PM
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The VCV is adjustable. The FSM shows you how to do it. You loosen two screws and turn the VCV until you start to feel resistance. I don't remember the details but you can get a CD-ROM of the W124 300D-T FSM from Mercedes.
Jeremy
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 "Buster" in the '95 Our all-Diesel family 1996 E300D (W210) . .338,000 miles Wife's car 2005 E320 CDI . . 113,000 miles My car Santa Rosa population 176,762 (2022) Total. . . . . . . . . . . . 627,762 "Oh lord won't you buy me a Mercedes Benz." -- Janis Joplin, October 1, 1970
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#3
06-22-2008, 04:36 PM
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Yes, I did that adjustment - it doesnt set how much it loses at idle, just the start and stop points of dumping vacuum. When it is off (idle) it is dumping 11inHG - going from 20 to 9 inHG, which is baaaaad.
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1983 240D Silver/Blue "Sadie", unknown miles. 100k miles on WVO single tank, converted to 2 tank about 10k miles ago, FPHE, Injector Heaters, Aux Fuel pump. Alcohol/Water injection. Frantz oil bypass filter 1992 300D 2.5 Turbo Green/Tan "Jade" 267K miles Stock. 1992 300D 2.5 tan/tan "Rocky" on 2 tank WVO. Pressure actuated Turbo "rat's nest" surgery completed. 197k miles
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#4
06-22-2008, 05:47 PM
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As I recall, my '87 300D-T starts out at about 15" Hg and ends up at about 5 or less. The manual says (and other forum members agree) that it should end up near zero (at full throttle).
My transmission shifted rather firmly until I adjusted the VCV; the low end was about 8" to 10" Hg and is now 5" Hg or less. Shifts now are much more reasonable. I also adjusted toe bowden cable to delay the shifts a little and that also seems to have helped the shifting.
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"Buster" in the '95 Our all-Diesel family 1996 E300D (W210) . .338,000 miles Wife's car 2005 E320 CDI . . 113,000 miles My car Santa Rosa population 176,762 (2022) Total. . . . . . . . . . . . 627,762 "Oh lord won't you buy me a Mercedes Benz." -- Janis Joplin, October 1, 1970
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