TH350/400 Governor Mods

 

TH350/400 Governor Mods

 

 

In the previous issue I explained how the governor plays the major role in determining the automatic shift points in Drive for TH350 and TH400 transmissions. If the rear axle ratio has been changed or the trans originally came from a different vehicle, the governor calibration is probably off and should be changed. But first ensure the vacuum modulator is OK and there are no vacuum leaks. The governor is a pressure valve with centrifugal flyweights and springs. It has outer (primary) and inner (secondary) weights, two each, and two springs. It's geared to the trans output shaft. The governor weights can be changed or ground down (to reduce weight) and the springs can be changed. If your shifts occur too soon you need lighter springs and/or smaller weights. If the shifts are too late, you need stiffer springs, or possibly heavier weights if your trans was originally in a vehicle with a higher numerical axle ratio. Governor spring and weight kits with detailed instructions are available from www.tciauto.com, B & M, and others for around $50. However you can modify a governor yourself to raise shift points with a bench grinder and two 6d finish nails.


The governor is located at the rear of the main trans case on the driver side on a TH 350 and passenger side on a TH400. There is a round sheetmetal cover over it that's held by a spring clip (or in some cases just an interference fit) on a TH350 and by 4 bolts or a spring clip on TH400's. Remove the cover (be sure to save the rubber O-ring seal) and the governor will slide straight out with a turning motion (it has a gear on the inside end). A small amount of trans fluid may leak out so put a pan under the opening. Now is a good time to check the governor shaft for wear. If the lands look worn or mike less than .799, or the gear is worn, get a new governor. You can get new governors and other rebuild parts at www.bulkpart.com. New governors are about $35.


If you want to raise the shift points without spending any money, you can grind some weight off the governor inner and outer flyweights. This will be trial and error until the shift points are where you want them. The inner weights are the secondary weights and mainly affect full throttle 1-2 and 2-3 shifts. Small amounts of weight removal are recommended on those. The outer weights are the primary weights and mainly affect the part-throttle 1-2 shifts. It takes more weight removal on those. To remove the weights, grind off the swedged ends of the two hinge pins and remove them. To reinstall the weights, use two 6d finish nails for hinge pins and bend the ends over to retain them after installing. Be sure both springs are back in place. Clean everything in parts cleaner before reinstalling the governor in the trans. As I mentioned, it will be a trial and error project, so if you're grinding weights, don't grind too much off at once. It's much easier changing just the springs than changing and/or grinding weights.


BTW, one more tip. On TH350's, the carb-to-trans kickdown cable must be adjusted correctly for part-throttle and full-throttle downshifts. The cable should reach the limit of its travel (full extension) just as the carb reaches WOT. TH400's have an electrical kickdown with a throttle or linkage mounted switch that should be adjusted to activate at WOT.