TH400 rebuild tech
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| − | == | + | ==TH400 transmission rebuild tech== |
'''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/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. | *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. | ||
| − | 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 | + | 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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[[file:Shift_seal_tool.jpg]] | [[file:Shift_seal_tool.jpg]] | ||
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| + | {{!}}The following was added by registered user 184.71.102.174: | ||
| + | <blockquote>Note: I'm a builder with 35 yrs experience and we have a full machine shop with bore gauges. We do not replace any bushings unless absolutely necessary in any transmission. All the aftermarket bushings I have ever used except ones that are designed to be machined after installation, ALWAYS result in GREATER clearance that the OEM bushing your replacing. If you shrink them in dry ice and tap them in you will have better results but they still maybe larger than OEM. The only bushing we change consistently is the front pump. We prefer to find another part with a good bushing. | ||
| + | </blockquote><br> | ||
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===Main case bushing replacement=== | ===Main case bushing replacement=== | ||
A universal cam bearing tool can be used to replace many bushings in the various automatics. It will not do very small bushings. Pictured here driving the bushing out towards the front. | A universal cam bearing tool can be used to replace many bushings in the various automatics. It will not do very small bushings. Pictured here driving the bushing out towards the front. | ||
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[[file:Rearbushingdriver.jpg]] | [[file:Rearbushingdriver.jpg]] | ||
| − | A | + | A TH400 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 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 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 TH350 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 endplay on the tight side. On a | + | 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. |
===Rear planetary setup=== | ===Rear planetary setup=== | ||
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[[file:Seal_rings_t-400.jpg]] | [[file:Seal_rings_t-400.jpg]] | ||
| − | *Cast iron is what most kits will contain, and what was used stock in most | + | *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 | + | *Scarf cut teflon was used on later models of the TH400. |
| − | *Solid teflon is used on | + | *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. | + | 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. |
| − | + | {{Note1}} 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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===Sprag design comparison=== | ===Sprag design comparison=== | ||
| − | The next picture shows a common roller clutch style drum and a roller clutch on the left, most | + | 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. |
| − | The 4L80E direct drum uses a sprag race that is 0.045 to 0.050 wider than the | + | 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. |
| − | [[File:Sprag-drum-compare.jpg|thumb|300px|left| | + | [[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. | ||
| − | [[File:T-400_direct_piston2.jpg|thumb|300px|left| | + | [[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. | ||
| − | [[File:T-400_direct_piston.jpg|thumb|300px|left| | + | [[File:T-400_direct_piston.jpg|thumb|300px|left|TH400 piston with springs]] <br style="clear:both"/> |
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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 TH400 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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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. | ||
| − | [[file:T-400_modulator_plug. | + | [[file:T-400_modulator_plug.jpg]] |
==Valve body mods, automatic shifts== | ==Valve body mods, automatic shifts== | ||
| − | The | + | The TH400 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 TH400. 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 TH400 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 TH400 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|TH400 governor with cover]] <br style="clear:both"/> |
==Vacuum modulator== | ==Vacuum modulator== | ||
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