i have a 84 300d turbo diesel it runs ok except it shifts to high gear too soon i get a lot of strange looks as other cars pass by dose the valve on top of valve cover regulate vacuum to trans .is the reason its shifting too soon a lack of vacuum. when i press throttle down dose it admit vac to trans or prevents vac going to trans also when i am slowing to stop it goes clunk when its cold as it warms up it shifts down ok i hope someone help me with this problem thanks.

Sounds like you may have a vac modulator leaking (or a plastic line). The system starts at about 15ihg when you start driving; the vac bleeds off as you accelerate and the transmission shifts with lower and lower vac as you speed up. Mine bleeds off to zero in about two seconds and I get a smooth shift.

You must have vacuum to downshift smoothely when coming to a stop. Without vac you will get a clunk as you described. Sounds like a leak.

I would first test the plastic line going from the vacuum control valve (VCV) under the hood to the vac modulator. If it is good, then use a mityvac and pump up the vac modulator to see if it holds vac. If it does not, then replace the vac modulator.

Your problem could be the VCV but I would start with the vac modulator.

My understanding on my 82 which should be the same as an 84 is that shift timing has nothing to do with vacuum.

The Bowden cable adjusts shift timing, on a dodge it would be called the TV cable, depending on throttle value, it changes the shift points.

Shift firmness is controlled by vacuum. (Vacuum modulator is on top of Injector pump, black hose goes to modulator on passenger side of transmission)
Less vacuum makes a firmer shift.
More vacuum makes a softer shift.

Disconnect the vacuum line entirely, and you'll chirp tires at shifts, and put a lot of stress on the driveline as a result.

Too much vacuum will soften the shifts to where it shortens clutch life.

That is my understanding, correct me if I'm wrong!

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1982 300D (w123, "Grey Car")
1982 300D (w123, "Blue Car")
2001 Ford F150 "Clifford" (The Big Red Truck)
1997 Dodge Ram 2500 12V Cummins
1996 Dodge Ram 2500 12V Cummins
Previous Vehicles:
1995 E300D, 1980 300SD, 1992 Buick Century, 2005 Saturn Ion

Frequently the Bowden cable however, there have always been more issues than that on any new to me car that I've bought. I now plug all of the vac lines going to the cabin to be sure those leaks aren't affecting my adjustments.

Next, measure the vacuum at one of the main ports on the main vacuum line. If vacuum is good say 15" but look up the spec to be sure, go through the procedure to test and adjust the vacuum control valve. If it isn't good, disconnect the line at the vacuum pump and measure there. You need correct vacuum to get the trans set up well.

The FSM shows a disk but I made one by drilling a 1/8" hole in a nickle (US). It's close enough. NExt adjust the vacuum control module at the transmission. The transmission manuals I've downloaded don't go back far enough to cover the 722.303 or the .315 but the modules of a given color have similar specs regardless of year. Start there and modify for the firmness you like.

Finally, move onto the Bowden cable adjustment. Note that there are at least 2 cables for the 722.315 so you may have to order by VIN to get the correct one. The changeover was between 84 & 85. I don't know whether other 722.xxx transmissions had the same changeover confusion.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

thanks to all who helped with too soon shifter sorry took so long to reply other stuff got in way again thanks

Were you able to fix it?

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84 300D, 82 Volvo 244Gl Diesel