TH400 rebuild tech

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==T-400 transmission rebuild tech==
 
==T-400 transmission rebuild tech==
 
'''NOTE:'''
 
'''NOTE:'''
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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/Turbo-Hydra-Matic-350-Handbook-Sessions/dp/0895860511/ref=pd_sim_b_6 Turbo Hydra-Matic 350 Handbook] by Ron Sessions, and this post for those new to transmissions.  
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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.  
  
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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 T-400 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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[[file:Shift_seal_tool.jpg]]
 
[[file:Shift_seal_tool.jpg]]
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<br><br>
  
 
===Main case bushing replacement===
 
===Main case bushing replacement===
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The total thickness of the bearing as compared to the thrust and selective is very close, it is usually about 0.150" (#25 bit, 0.1495").   
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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]]
  
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It is best to adjust rear endplay 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.
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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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Once the intermediate apply piston and the return springs, guide, retainer plate and snap ring is installed, you must install the center support to direct drum sealing rings.
 
Once the intermediate apply piston and the return springs, guide, retainer plate and snap ring is installed, you must install the center support to direct drum sealing rings.
  
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There are 3 choices here.
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*There are three choices here, shown below:
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#Solid teflon is on the left
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Solid teflon is on the left, then scarf cut teflon, then cast iron.
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#Scarf cut teflon, center
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#Cast iron, right
  
 
[[file:Seal_rings_t-400.jpg]]
 
[[file:Seal_rings_t-400.jpg]]
  
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*Cast iron is what most kits will contain, and what was used stock in most T-400's. 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.
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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.
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*Scarf cut teflon was used on later model T-400's.
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*Scarf cut teflon was used on later models of the T-400.
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*Solid teflon is used on 4L80s 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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*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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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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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.
  
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Notice I left one sealing ring 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 T-400 will be covered in more depth in another section.
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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.
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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. 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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The next picture shows a common roller clutch style drum and a roller clutch on the left, most T-400's will use this style drum. Early units, pre-'71, will have the smooth inner race style drum on the right. 4L80E's also use the "early" style drum and an actual sprag. The stock 16 element sprag is in the center, with the 34 element on the right.
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The next picture shows a common roller clutch style drum and a roller clutch on the left, most TH400 use this style drum. Early units, pre-'71, will have the smooth inner race style drum on the right. 4L80E's also use the "early" style drum and an actual sprag. The stock 16 element sprag is in the center, with the 34 element on the right.
  
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The 4L80E direct drum uses a sprag race that is 0.045 to 0.050 wider than the T-400 sprag race. If you acquire a 4L80E direct drum be sure to have the correct race too.
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The 4L80E direct drum uses a sprag race that is 0.045 to 0.050 wider than the TH400 sprag race. If you acquire a 4L80E direct drum be sure to have the correct race, too.
  
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[[File:Sprag-drum-compare.jpg|thumb|300px|left|T-400 roller clutch and early design sprag unit]] <br style="clear:both"/>
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[[File:Sprag-drum-compare.jpg|thumb|300px|left|TH400 roller clutch and early design sprag unit]] <br style="clear:both"/>
  
 
===Spiro loc retainer===
 
===Spiro loc retainer===
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Notice the circle around the check ball in the aluminum piston. Each drum and piston assembly must have one of these check balls. The check ball may be in the piston, it may be in the drum as circled in the drum photo.
 
Notice the circle around the check ball in the aluminum piston. Each drum and piston assembly must have one of these check balls. The check ball may be in the piston, it may be in the drum as circled in the drum photo.
  
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[[File:T-400_direct_piston2.jpg|thumb|300px|left|T-400 piston check ball location]] <br style="clear:both"/>
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[[File:T-400_direct_piston2.jpg|thumb|300px|left|TH400 piston check ball location]] <br style="clear:both"/>
  
  
 
You must install a ''full'' set of returns springs in the direct drum. Ignore the experts or online information to leave springs out of the direct drum. If you have a set of heavy duty return springs from a kit or supplier, install half HD springs with half OEM springs. This helps to avoid residual oil behind the piston from forcing the piston out at high RPM when in 1st or 2nd gears.
 
You must install a ''full'' set of returns springs in the direct drum. Ignore the experts or online information to leave springs out of the direct drum. If you have a set of heavy duty return springs from a kit or supplier, install half HD springs with half OEM springs. This helps to avoid residual oil behind the piston from forcing the piston out at high RPM when in 1st or 2nd gears.
  
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[[File:T-400_direct_piston.jpg|thumb|300px|left|T-400 piston with springs]] <br style="clear:both"/>
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[[File:T-400_direct_piston.jpg|thumb|300px|left|TH400 piston with springs]] <br style="clear:both"/>
  
  
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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.
  
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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.   
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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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After the boost valve modification, you can install an aluminum plug that blocks the modulator valve in place. The original bolt and bracket from the vacuum modulator holds the aluminum plug in place.
 
After the boost valve modification, you can install an aluminum plug that blocks the modulator valve in place. The original bolt and bracket from the vacuum modulator holds the aluminum plug in place.
 
   
 
   
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[[file:T-400_modulator_plug.jpg‎ ]]
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[[file:T-400_modulator_plug.jpg]]
  
 
==Valve body mods, automatic shifts==
 
==Valve body mods, automatic shifts==
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===Drum installation===
 
===Drum installation===
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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 TH2004R. 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.
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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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[[File:T-400_governor.jpg|thumb|300px|left|T-400 governor with cover]] <br style="clear:both"/>
 
[[File:T-400_governor.jpg|thumb|300px|left|T-400 governor with cover]] <br style="clear:both"/>
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==Vacuum modulator==
 
==Vacuum modulator==
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[[File:Bm-20297.jpg]]
 
[[File:Bm-20297.jpg]]
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==Line pressure==
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<table table border="1" cellpadding="2" cellspacing="0" >
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<tr><td bgcolor="#CCCCCC" valign="top" width="37%"><font face="Arial">        <b><font face="Arial" size="3">Range</font></b>
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              </font></td>
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<td bgcolor="#CCCCCC" valign="top" width="30%"><font face="Arial">            <b><font face="Arial" size="3">Minimum</font></b>
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              </font></td>
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<td bgcolor="#CCCCCC" valign="top" width="33%"><font face="Arial">            <b><font face="Arial" size="3">Maximum</font></b>
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              </font></td>
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            </tr>
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<tr><td bgcolor="#FFFF00" valign="top" width="37%"><font face="Arial"><b><font face="Arial" size="2">Park</font></b></font></td>
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<td bgcolor="#FFFF00" valign="top" width="30%"><font face="Arial">            <b><font face="Arial" size="2">55-70</font></b>
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              </font></td>
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<td bgcolor="#FFFF00" valign="top" width="33%"><font face="Arial">            <b><font face="Arial" size="2">150-175</font></b>
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              </font></td>
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            </tr>
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<tr><td bgcolor="#FFFFFF" valign="top" width="37%"><font face="Arial"><b><font face="Arial" size="2">Reverse</font></b></font></td>
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              <td valign="top" width="30%"><font face="Arial">                <b><font face="Arial" size="2">95-150</font></b>
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              </font></td>
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<td valign="top" width="33%"><font face="Arial">                <b><font face="Arial" size="2">235-260</font></b>
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              </font></td>
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            </tr>
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<tr><td bgcolor="#FFFF00" valign="top" width="37%"><font face="Arial"><b><font face="Arial" size="2">Neutral</font></b></font></td>
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<td bgcolor="#FFFF00" valign="top" width="30%"><font face="Arial">            <b><font face="Arial" size="2">55-70</font></b>
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              </font></td>
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<td bgcolor="#FFFF00" valign="top" width="33%"><font face="Arial">            <b><font face="Arial" size="2">150-175</font></b>
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              </font></td>
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            </tr>
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<tr><td bgcolor="#FFFFFF" valign="top" width="37%"><font face="Arial"><b><font face="Arial" size="2">Drive</font></b></font></td>
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<td valign="top" width="30%"><font face="Arial">                <b><font face="Arial" size="2">70-90</font></b>
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              </font></td>
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<td valign="top" width="33%"><font face="Arial">                <b><font face="Arial" size="2">135-165</font></b>
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              </font></td>
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            </tr>
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<tr><td bgcolor="#FFFF00" valign="top" width="37%"><font face="Arial"><b><font face="Arial" size="2">Second</font></b></font></td>
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<td bgcolor="#FFFF00" valign="top" width="30%"><font face="Arial">            <b><font face="Arial" size="2">135-165</font></b>
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              </font></td>
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<td bgcolor="#FFFF00" valign="top" width="33%"><font face="Arial">            <b><font face="Arial" size="2">135-165</font></b>
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              </font></td>
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            </tr>
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<tr><td bgcolor="#FFFFFF" valign="top" width="37%"><font face="Arial"><b><font face="Arial" size="2">Low</font></b></font></td>
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<td valign="top" width="30%"><font face="Arial">                <b><font face="Arial" size="2">135-165</font></b>              </font></td>
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<td valign="top" width="33%"><font face="Arial"><b><font face="Arial" size="2">135-165</font></b></font></td></tr></table><br>
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'''Note:''' Line pressure fitting is located on driver side of transmission close to shift lever.
  
 
==Transfer case info==
 
==Transfer case info==
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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)...
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*TH400 to NP203 = 1-3/8" (1.1" adapter)
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*T-400 to NP203 = 1-3/8" (1.1" adapter)
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*TH400 to late NP205/NP208 = 2-1/2"
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*T-400 to late NP205/NP208 = 2-1/2"
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*TH400 to early NP205 = 4-1/2" (same as short 2WD output)
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*T-400 to early NP205 = 4-1/2" (same as short 2WD shaft)
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[[Category:Transmission]]
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[[Category:good articles]]
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Latest revision as of 16:16, 18 August 2023

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