TH400 rebuild tech

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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.  
  
The original article by jakeshoe can be seen in the Hotrodders forum thread '''''[http://www.hotrodders.com/forum/t-400-build-tips-photos-145318.html TH400 Build Tips with Photos]'''''.
 
  
 
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 TH350 pump shims as pictured on the left here:
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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 TH400 (unless it has straight cut planetary gears) the planets will try to thrust load against the case bearing and the center support.
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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 TH400.
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*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.
  

Revision as of 11:43, 28 July 2023

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