i have a 78 300d
my a/t will not shift

can this be caused by lack of vacuum?
i have no vacuum lines run to trans

I was hoping someone would answer this, because I have almost exactly the same issue with my 82 240D.

But as a long-time DIYer, and having perused the forums, vacuum diagrams and trans shift problem discussions, I would say that you are right. I am assuming mine is weak vacuum, since it shifts 1->2 if I run up to about 25 mph, then I get a monstrous hard shift complete with neck-jerk and wheel chirp (in a 240D!) and it goes into 2nd. Won't shift to 3rd or 4th.

So go ahead and buy the parts, read the instruction manuals (Skinnerbox has them - http://skinnerbox.steaky.org ) and put the vacuum system back into proper order. Then if you still have a problem start digging deeper.

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To hear the gods laugh, tell them your plans.

I too am having issues with mine not wanting to shift up until its about redlined, although it does eventually go up in all gears if revved enough and played with the throttle enough. I just found the adjustments page this morning and thought I would go thru that, being this car hasn't run for 4 yrs and I just transplanted the engine. Upon initial inspection, all mechanical adjustments seemed to be where they ought to, so I began looking into the vacuum side of it, what I found was that several of the vacuum lines looked good, but had gone hard & crusty @ the nipples, would slide off easily if provoked, especially under the black plastic cover on the central vac. valve on top of the valve cover (where nobody ever looks). I also found the P.O. or past mechanic had gotten into things and had the vac hoses all muddled up so that no supply was actually connected to the trans modulator (went to a valve in the cent. vac. valve and the other sides of the valve went to nothing) and they had also plumbed the other switch in the valve so that when you pull off idle it opens the vacuum pump line to atmosphere.....
I found some good diagrams here and will be in process of replumbing things this morning.

**Ok, that was the problem, I got the lines rerouted properly and now it shifts (almost) properly. I believe the P.O attempted to make a repair of something, got the lines crossed up or tried to rig around something, caused the tranny to stop shifting, kept on driving it either not caring or trying to get by, causing the engine to spend way too much time at extreme speeds, which is what sent the rod out the side of the block on the original motor. Now that I have the trans vacuum back to right, it is shifting too soon now, lugging the engine, I am willing to bank I will find that after they messed up the vacuum control, they fudged with the modulator trying to compensate.
-Chris

It isn't from lack of vacuum, there is no vacuum modulator for a '78 or '79, I have had them both. I have a working transmission from my '78 should you not be able to fix yours. -Andy

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andy t
'78 300d
'95 volvo 850, wagon
'86 300sdl - engine out, maybe I'll have it rolling by June

whole bunch o' bicycles