I found a pretty good vac diagram in the Performance Products catalog. After playing around, I found inconsistant readings from the top side of the vacuum valve. That blue thing in the corner near the drivers side firewall.
The first time I read the line that goes to the trans, it read 15" at idle and 12" with the throttle open. After checking other lines, I checked the tranny line again, it read 5" and dropped to 2" revved.
I checked other lines and went back to the vacuum valve and checked the tranny line one more time and it read 15" as before.
Before I did my tests, the tranny was making a "clunk" sound when you would come to a stop. After, it shifted and downshifted as it should.
The vacuum pump is reading 23" at idle with little change throttled up.
It seems to me that the pump is O.K. and the Vacuum Valve is suspect. Does it sound like I'm on the right track?
Thanks for your help,
84 300SD (sold)