TH400 rebuild tech
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Use a stock bushing, red loctite in place, and staked in place. | Use a stock bushing, red loctite in place, and staked in place. | ||
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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. | ||
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| + | 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. | ||
| + | Pictured here, bearing is on top: | ||
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| + | You set rear endplay using TH350 pump shims as pictured on the left here: | ||
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| + | The total thickness of the bearing as compared to the thrust and selective is very close, it is usually about .150". | ||
| + | It is best to adjust rear endplay on the tight side. On a Th400 (unless it has straight cut planetary gears) the planets will try to thrust load against the case bearing and the center support. | ||
| + | I disassemble the rear output shaft from the output ring gear and clean and inspect the planets. Refer to manual for checking procedures and specs. It is shown here re-assembled with the reaction carrier and sun gear ready to be re-assembled. | ||
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| + | Slide the reaction carrier onto the rear planet assembly, drop in the sun gear, flat side toward the front of trans. | ||
| + | Then slide the reaction tube in, shown to the rear: | ||
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| + | It is best to have the center support already ready. | ||
| + | The center support houses the intermediate apply piston, supports the direct drum. It has sealing rings that seal it to the direct drum, allowing it to transfer fluid to the drum to apply 3rd gear, and reverse. | ||
| + | Disassemble, clean, and re-assemble using new lip seals. Pay attention to the orientation. Use the old lip seals to be sure you select the properly sized new seals. | ||
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| + | Install the piston using a lip seal installed or feeler guage, be sure the piston depressions aling with the depressions in the center support, and it helps to use a tilting motion as you install it sometimes. | ||
| + | You can also use thin plastic (cut from a large plastic soda bottle) as a seal protector/installer or the proper Kent-Moore J-tools. | ||
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| + | Once the intermediate apply piston is installed and the return springs, guide, retainer plate and snap ring, you must install the center support to direct drum sealing rings. | ||
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| + | There are 3 choices here. | ||
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| + | Solid teflon is on the left, then scarf cut teflon, then cast-iron. | ||
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| + | Cast iron is what most kits will contain, and what was used stock in most TH400's. | ||
| + | Scarf cut teflon was used on later model Th400's. | ||
| + | Solid teflon is used on 4L80's and is interchangeable. | ||
| + | I prefer solid teflon, although it is the most time consuming type. | ||
| + | Cast iron is the easiest and will work fine for most applications but if using any type of valve body that will not require a modulator teflon is best as it will prevent wear on the direct drum. | ||
| + | If using teflon, be sure there are no burrs on the center support ring grooves. | ||
| + | Installing the teflon rings requires a protector to prevent cutting or gouging them, and a sizing device. | ||
| + | It helps to heat the rings in hot water before installing so that they will stretch easier. | ||
| + | I use a piece of plastic (from a paint can cap) that is cut to size to install and size the rings. Leave it on until you are ready to install the direct drum. | ||
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| + | Notice I left one sealing ring off, 2nd from top groove. This groove seperates the direct (3rd gear) and reverse feeds from each other. When dual feeding the directs (as done in this build), this sealing ring is not necessary. Dual feeding the directs on a Th400 will be covered in more depth in another section. | ||
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