Having problem with the up shifting into the 4th. high range .It will shift up at the marked speedo ranges 15 first- 28 second 58 third to 4th,but will not go into 4th at any other speed when you let up ont he pedal for normal 4th range driving- seems to be a vacum switch with 3 hoses on top of the engine a 4thport blocked with a screw. One hose goes down to the side of the tranny for shifting others go to various vacum ports IT was driven from Florida to Pa. by shifting manually L-S-to Drive Otherwise it stayed in 4th range at all times I reversed lines at switch on top of engine which gave me the proper shifting except for the 4th range. Could I have a faullty plastic vacum switch or the port that is blocked with screw go to something. Also tryed adjusting throttle linkage to no avail. ANY IDEAS --Thanks DON at DVW

You are in the right area!
Vacuum to the modulator controls both how hard & WHEN this trans shifts.
"T" a vacuum guage into the vacuum line that goes to the modulator & drive the car(watch the gauge inside of the car). Vacuum should be high at idle & with foot off of the fuel pedal. At full throttle there shouldn't be any vacuum. In-between the vacuum should go up OR down depending on pedal position.

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