Editing TH400 rebuild tech (section)
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===Full manual shift modifications=== FULL manual shifts means just that. You must move the shifter for every shift up or down. NO Automatic shifts. There are two steel governor fluid tubes out the rear of the main valve body. Remove these tubes. Plug the holes in valve body. 3/8-16 tap and set screws work. Use a liquid thread locker like Loctite. [[image:Gov_tube_holes.jpg]] A new 0.110" (#35 or 7/64" bit) hole needs to be drilled in the proper place to loop the governor fluid. Check photos here for location. [[file:T-400_full_manual_loop03.jpg]] You must also modify the 1-2 shift valve as listed below for FULL manual shift conversion: The T-400 has a over-ride shift that will shift out of low gear even if you have manually selected low. It was designed to prevent engine damage. You can eliminate this feature by performing the following modifications to the valve body. You must remove the 1-2 shift valve and grind two flats on the land designated by the arrow. You must plug the exhaust hole in the valve body also designated. [[file:1-2_shift_valve.jpg]] Simply grind two flats on the shift valve and deburr them. You can plug the hole with a brass dowel or a check ball. To use a check ball you will have to first drill the hole larger and then drive the check ball in place. Drill the marked holes to .125" (1/8") for street use. At the 1-2 shift hole location (designated #2), drill the small hole out. For a heavy duty application: 3rd gear shift use a .150" drill (#25 bit, .149) and leave the 1-2 check ball out. '''Caution:''' A 34 element sprag needs to be used with the 1-2 check ball removed. Near the bottom of the separator plate in photo, the hole in the round black circle (designated 'Dual Feed') should be plugged when the dual feed modifications are performed with the center lip seal removed from the direct clutch drum. [[file:T-400_feed_holes03.jpg]] Another mod is blocking the 2-3 accumulator. I do this with a set screw. You tap the hole and install the set screw available from any hardware store. You will remove the 2-3 accumulator piston, discard the spring. This firms up the 2-3 shift. Re-Install the piston in the hole. Do not use a plastic piston, they break. Tap the hole that feed the backside, or spring side, of the accumulator piston. Install the set screw. Re-install the accumulator piston. What this does is eliminates accumulator function on the 2-3 shift. This results in a very positive 2-3 shift. You could leave 2-3 accumulator function in place and go slightly bigger on the feed hole. [[file:100_2218-1.jpg]]
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