TH400 rebuild tech
From Crankshaft Coalition Wiki
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*This information and photos are meant to help those who wish to rebuild their own transmission, however this is not intended to be a replacement for an ATSG or factory tech manual. First time builders will likely need a tech manual. Recommended is an ATSG rebuild manual, and [http://www.amazon.com/Rebuild-Modify-Transmissions-Design-Workbench/dp/1934709204/ref=pd_bxgy_b_img_y How to Rebuild & Modify GM Turbo 400 Transmissions (S-A Design Workbench Series)], and this post for those new to transmissions. | *This information and photos are meant to help those who wish to rebuild their own transmission, however this is not intended to be a replacement for an ATSG or factory tech manual. First time builders will likely need a tech manual. Recommended is an ATSG rebuild manual, and [http://www.amazon.com/Rebuild-Modify-Transmissions-Design-Workbench/dp/1934709204/ref=pd_bxgy_b_img_y How to Rebuild & Modify GM Turbo 400 Transmissions (S-A Design Workbench Series)], and this post for those new to transmissions. | ||
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Besides the basic rebuild, also shown here are some modifications that are not usually required, but are still good to do. | Besides the basic rebuild, also shown here are some modifications that are not usually required, but are still good to do. | ||
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| − | You set rear end play using | + | You set rear end play using T-350 pump shims as pictured on the left here: |
[[file:Rear-thrustshim.jpg]] | [[file:Rear-thrustshim.jpg]] | ||
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[[file:Rear-bearing-measure.jpg]] | [[file:Rear-bearing-measure.jpg]] | ||
| − | It is best to adjust rear end play on the tight side. On a | + | It is best to adjust rear end play on the tight side. On a T-400 (unless it has straight cut planetary gears) the planets will try to thrust load against the case bearing and the center support. |
===Rear planetary setup=== | ===Rear planetary setup=== | ||
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*Cast iron is what most kits will contain, and what was used stock in most TH400 transmissions. 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. | *Cast iron is what most kits will contain, and what was used stock in most TH400 transmissions. 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. | ||
| − | *Scarf cut teflon was used on later models of the | + | *Scarf cut teflon was used on later models of the T-400. |
*Solid teflon is used on the 4L80 series and is interchangeable. I prefer solid teflon, although it is the most time consuming type. 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. | *Solid teflon is used on the 4L80 series and is interchangeable. I prefer solid teflon, although it is the most time consuming type. 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. | ||
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You must also modify the 1-2 shift valve as listed below for FULL manual shift conversion: | You must also modify the 1-2 shift valve as listed below for FULL manual shift conversion: | ||
| − | The | + | 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 can eliminate this feature by performing the following modifications to the valve body. | ||
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==Valve body mods, automatic shifts== | ==Valve body mods, automatic shifts== | ||
| − | The | + | 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 can eliminate this feature by performing the following modifications to the valve body. | ||
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===Drum installation=== | ===Drum installation=== | ||
| − | Then the intermediate clutch stack is 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 lugs here in the case are one of the weak points of a | + | Then the intermediate clutch stack is 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 lugs here in the case are one of the weak points of a T-400. High line pressure, harsh shift calibration, and fatigue 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 the T-400 line pressure under 250 psi if possible. |
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. | 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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===Governor=== | ===Governor=== | ||
| − | Photo of the | + | Photo of the T-400 governor and cover. Note the direction the plastic drive gear teeth. The plastic drive gear can wear out or break. This result in no upshifts since the governor is not rotating. |
| − | [[File:T-400_governor.jpg|thumb|300px|left| | + | [[File:T-400_governor.jpg|thumb|300px|left|T-400 governor with cover]] <br style="clear:both"/> |
==Vacuum modulator== | ==Vacuum modulator== | ||
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;Output shaft lengths (from the back of the case to the end of the shaft): | ;Output shaft lengths (from the back of the case to the end of the shaft): | ||
Output shaft lengths (from the back of the case to the end of the shaft)... | Output shaft lengths (from the back of the case to the end of the shaft)... | ||
| − | * | + | *T-400 to NP203 = 1-3/8" (1.1" adapter) |
| − | * | + | *T-400 to late NP205/NP208 = 2-1/2" |
| − | * | + | *T-400 to early NP205 = 4-1/2" (same as short 2WD shaft) |
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