TH400 rebuild tech
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[[image:400v-body-7.JPG]] | [[image:400v-body-7.JPG]] | ||
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| + | ===Valve body mods, automatic shifts=== | ||
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| + | The TH400 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. | ||
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| + | 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. | ||
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| + | [[file:1-2_shift_valve.jpg]] | ||
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| + | 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. | ||
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=Jakeshoe rebuild tech:= | =Jakeshoe rebuild tech:= | ||
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If you plan on using a rear torrington type bearing you want to place the bushing ever so slightly protruding to the front, so that it will locate the bearing. | If you plan on using a rear torrington type bearing you want to place the bushing ever so slightly protruding to the front, so that it will locate the bearing. | ||
| − | I use a TH350 pump -direct drum bearing from a later style TH350. These can be ordered new (preferred). | + | I use a TH350 pump -direct drum bearing from a later style TH350. These can be ordered new (preferred). This torrington bearing replaces the stock thrust washer and rear selective tang washer in the TH400. |
| − | This torrington bearing replaces the stock thrust washer and rear selective tang washer in the TH400. | + | |
Pictured here, bearing is on top: | Pictured here, bearing is on top: | ||
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| − | You set rear | + | You set rear end play using TH350 pump shims as pictured on the left here: |
[[file:Rear-thrustshim.jpg]] | [[file:Rear-thrustshim.jpg]] | ||
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A stock snap ring can also be tack welded to the retainer. The TIG welding method with silicon bronze is best. Most DIY folks at home do not access to this method | A stock snap ring can also be tack welded to the retainer. The TIG welding method with silicon bronze is best. Most DIY folks at home do not access to this method | ||
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| + | ===Drum installation=== | ||
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| + | This is the intermediate clutch stack assembled into the case on top of the center support. There is a snap ring that goes in the case above the pressure plate pictured. The splined case luges here in the case are one of the weak points of a TH400, high line pressure, harsh shift calibration, and fatique cause the lugs to break here. TransGo kits contain a heavy snap ring to help this, I use a center support snap ring from a 200-4R. Some performance vendors sell a brace that helps prevent case lug breakage. | ||
| + | One of the keys is to keep line pressure under 250 psi if possible. | ||
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| + | photo needed | ||
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| + | This is the direct drum sitting in the case. The sprag race engages the intermediate clutches. If using a valve body with engine braking, be sure you install the intermediate band. | ||
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| + | [[file:Direct_drum_install.jpg]] | ||
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| + | Next goes the forward drum: | ||
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| + | [[file:Fwd-druminstall.jpg]] | ||
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| + | Case is prepared for pump installation. | ||
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| + | More to follow as I finish this build. | ||
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| + | I will cover intermediate clutch installation, direct drum assembly, forward drum assembly, pump inspection and assembly, air checks, dual feeding modifications, 34 element intermediate sprag vs. stock 16 element and later roller clutch as well as various assembly tips to improve the TH400. | ||
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| + | OK, | ||
| + | Making your own valve body kit. | ||
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| + | The TH400 doesn't require anything super fancy to get a firm shifting unit. | ||
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| + | You need to drill the feed holes shown in this picture. I recommend drilling them both to .125". The 3rd feed hole can go bigger, but I would recommend .140" as the high end. | ||
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| + | You also block the 2-3 accumulator feed hole in the valve body. This requires a 5/16" set screw and proper tap. You will remove the 2-3 accumulator piston, discard the spring. | ||
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| + | Tap the hole that feed the backside, or spring side, of the accumulator piston. Install the set screw. Re-install the accumulator piston. | ||
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| + | 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. | ||
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