Rough shifting cured by replacing the brake booster line.
 

I've been bringing an 83 380 sel back to life for the last year. It has always shifted rougher that I think it should. I changed the fluid and filter, and had the vacuum modulator adjusted. Each helped a little but I still didn't think it was quite right. I've been prepared for a rebuild at some point.

However, last week as I was cleaning and lubricating the throttle linkage I bumped the brake booster line, which fell apart at the check valve. Close examination revealed that some previous owner had repaired it with a combination of JB Weld and black electrical tape. I taped it back up as best I could until the new line arrived yesterday. When I removed the old one I discovered that not only was it broken at the check valve but the fitting at the booster was just finger tight.

Now that what must have been a massive vacuum leak has been fixed the transmission shifts much smoother, and the engine has a lot more power. I can't believe such a simple repair made such a dramatic improvement.

So . . . if you've been chasing vacuum leaks, take a close look at your brake booster line. Maybe you'll find a hidden nightmare like I did.

Yup, just goes to show ya, DUCT tape and 5 minute epoxy is the only appropriate repair in a case like this.....electrical tape, boy I tell ya.......................

Gilly