TH400 rebuild tech
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| − | + | ==T-400 transmission rebuild tech== | |
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'''NOTE:''' | '''NOTE:''' | ||
| − | *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/ | + | *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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[[file:Shift_seal_tool.jpg]] | [[file:Shift_seal_tool.jpg]] | ||
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===Main case bushing replacement=== | ===Main case bushing replacement=== | ||
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[[file:Rearbushingdriver.jpg]] | [[file:Rearbushingdriver.jpg]] | ||
| − | A | + | A T-400 and 4L80E used in heavy towing will sometimes cause the rear bushing to "walk" to the rear, ruining the governor gear. There is a "fix" bushing for this that has a thrust surface on the front that prevents the bushing from walking. |
Use a stock bushing with red loctite and staked in place. | Use a stock bushing with red loctite 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. | 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 | + | I use a T-350 pump - direct drum bearing from a later style T-350. These can be ordered new (preferred). This torrington bearing replaces the stock thrust washer and rear selective tang washer in the T-400. |
Pictured here, bearing is at the top: | Pictured here, bearing is at the top: | ||
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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]] | ||
| − | The total thickness of the bearing as compared to the thrust and selective is very close, it is usually about 0.150" | + | The total thickness of the bearing as compared to the thrust and selective is very close, it is usually about 0.150" . |
[[file:Rear-bearing-measure.jpg]] | [[file:Rear-bearing-measure.jpg]] | ||
| − | It is best to adjust rear | + | 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. | ||
It helps to heat the rings in hot water before installing so that they will stretch easier. A piece of plastic (from a paint can cap) that is cut to size can be used to install and size the rings. Leave it on until you are ready to install the direct drum. | It helps to heat the rings in hot water before installing so that they will stretch easier. A piece of plastic (from a paint can cap) that is cut to size can be used to install and size the rings. Leave it on until you are ready to install the direct drum. | ||
| − | + | One sealing ring has been left off, 2nd from top groove. This groove separates 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. | |
[[File:Center_support_rings.jpg]] | [[File:Center_support_rings.jpg]] | ||
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| − | Pictured is a late style reaction carrier (left) and an early style. I believe the early style was only used on 1964-1966 models. Notice the actual sprag-type element used on the early style on the right. I prefer these types for high HP transbrake builds although not mandatory. | + | Pictured is a late style reaction carrier (left) and an early style. I believe the early style was only used on 1964-1966 models. Notice the actual sprag-type element used on the early style on the right. I prefer these types for high HP transbrake builds although not mandatory. Early style reaction carrier is also found in some HD versions of the THM400 used in medium duty Chevrolet/GMC trucks and the 1991-up 4L80E. |
[[file:planets.jpg]] | [[file:planets.jpg]] | ||
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[[file:T-400_intermed_clutch.jpg]] | [[file:T-400_intermed_clutch.jpg]] | ||
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===Sprag design comparison=== | ===Sprag design comparison=== | ||
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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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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. | 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 used with the 1-2 check ball removed. | + | 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. | 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. | ||
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[[file:100_2218-1.jpg]] | [[file:100_2218-1.jpg]] | ||
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===Boost valve modification=== | ===Boost valve modification=== | ||
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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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