Originally Posted by Maroon 300D

The good news: I believe I have figured out the cause of the rough shifting I've been getting on cool mornings.

The bad news: It's a climate control leak! This is bad because I was hoping I wouldn't have to take the dash apart to fix this problem.

This morning I got up a little early and tested the vac to my transmission. It registered at just under 6" hg at idle, down from 20.5" hg at idle when it's warm out (ambient temp.). Now before you freak out about the 20.5 number, realize I have an '85 CA car and the vacuum is a little different on it. In other words, the numbers on Diesel Giant's site and in other places may not be right for my car. I don't know what they should be, though...so if you have any thoughts, please chime in.

Now it was a bit dewy this morning so I used the defrost, which I haven't touched in a while...and the shifting was great! I did some more experimenting and sure enough, smooth shifting with defrost on and hard shifting with it off. Previously I'd tried the climate control in various positions - different temps and settings - and it hadn't seemed to make a difference. Guess maybe I'd neglected defrost. I'd also given some vacuum to the blue/green line that I think goes to the climate control and it held the vacuum, but that was when it was warm out and the problem only surfaces when it's cool.