When I step hard on the gas, the car seems to shift normally. When going slow/light on the gas, the car shifts rather abruptly on shifts 2-3 and 3-4 and also on downshifts. I'm thinking perhaps the vacuum control valve (VCV) might need replacement??

When I changed my Oil Filter Housing Gasket I inadvertently disconnected the Vacuum Line to the Transmission Modulator.

When I drove the Car the forward acceleration shifts were nearly normal but deceleration down shifts were very harsh.

In you case I would be looking for vacuum leaks and be sure that the Cap on the Transmission Modulator is there and that the Cap is not cracked.

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84 300D, 82 Volvo 244Gl Diesel

You can easily track down vac leaks with a Mityvac. Do that first before you adjust the vacuum modulator. As you know a 300TD is designed to bleed the vac down to zero for upshifts and uses vac for downshifts only. The vac modulator adjusts the firmness of the shifts.

Not exactly. There is a restricted fitting in the line going to from the main vacuum to the vacuum line. That reduces the vaccum to a set amount From that set amount it goes by how much movement/angularity of throttle when you step on the accelerator pedal.

So you start off with that preset restricted amount of vacuum and as you depress the accelerator the vacuum decreases and it can go down to zero if that is what it takes to get it to work (adjusted at the vacuum valve).

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84 300D, 82 Volvo 244Gl Diesel

Either today or tomorrow I am going to check all of the vacuum lines both from the top of the engine and underneath the car where the vacuum line connects to the transmission modulator.

About two weeks ago, the engine coolant feed hose (the one that is twisted like a snake and goes from the firewall to the engine block feeding over the oil filter) failed.

Fortunately, I had a new one on hand so I replaced it and in the process accidentally knocked loose the vacuum hose going into the VCV. I found the problem immediately and fixed it. So......I may have also accidentally knocked some other vacuum hoses loose....will report back after I check them out.

Diesel911 is right. The VCV (vac control valve) is located under the hood and redirects vac to the tranny. In effect though the vac which starts out at 12-15 quickly goes to zero when you hit the throttle.

I checked the vac line going into the modulator, it is connected properly. Two issues, I have the old dark green modulator, do I need to purchase the newer light green modulator? Secondly, the bowden cable appears broken at the top of the engine (plastic adjustment screw).

Obviously, I need to acquire a new bowden cable; can I drive the car safely until it arrives?

Attached Thumbnails

   

I located the following post from forum member Bill Grissom. It seems like his fix would work......

"If that old brittle plastic adjuster breaks, as it did on both my 300D's, you can cut a 1/4" copper tube to length, w/ a lengthwise slit to slip over the cable, and it will set the adjustment length."

bump

Here is a pretty decent write up on tuning the trans.

The file I wanted is too large to upload.

Here it is. Some of the other files may be of interest also.
https://ln2.sync.com/dl/71244f250/4gff6c4h-tpjdjhsw-aeg94h38-twxn9yy3

Attached Files

722 MBZ Transmission.pdf (130.4 KB, 56 views)

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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.

Jman - you forgot the link.