TH400 rebuild tech
(→Clearance in clutch packs:) |
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| − | =Rebuilding the | + | =Rebuilding the TH400= |
The following information is the work of "Jakeshoe" and appears on various forums/threads, like- [http://www.hotrodders.com/forum/t-400-build-tips-photos-145318.html] | The following information is the work of "Jakeshoe" and appears on various forums/threads, like- [http://www.hotrodders.com/forum/t-400-build-tips-photos-145318.html] | ||
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[[image:Gov_tube_holes.jpg]] | [[image:Gov_tube_holes.jpg]] | ||
| − | A new hole in the proper place needs to be drilled | + | A new 0.110" (#35 or 7/64" bit) hole in the proper place needs to be drilled to loop the governor fluid. Check photos here for location |
[[file:T-400_full_manual_loop03.jpg]] | [[file:T-400_full_manual_loop03.jpg]] | ||
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You can plug the hole with a brass dowel or a check ball. To use a check ball you will have to first drill the hole larger and then drive the check ball in place. | You can plug the hole with a brass dowel or a check ball. To use a check ball you will have to first drill the hole larger and then drive the check ball in place. | ||
| − | Drill the marked holes at .125 for street use. | + | Drill the marked holes at 0.125" (1/8") for street use. |
| − | For a heavy duty application : 3rd gear shift use .150 drill 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 0.150" drill (#25 bit, 0.1495") and leave the 1-2 check ball out. Caution a 34 element sprag needs to used with the 1-2 check ball removed. |
[[file:T-400feed-holes.jpg]] | [[file:T-400feed-holes.jpg]] | ||
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Modification of the boost valve to have static line pressure and vacuum modulator replaced with aluminum plug. This modification of the boost valve avoids the run away high line pressure in reverse. | Modification of the boost valve to have static line pressure and vacuum modulator replaced with aluminum plug. This modification of the boost valve avoids the run away high line pressure in reverse. | ||
| − | Grind a flat spot on the large spool valve land with arrow pointed at it. It is not fussy, 1/4 to 3/8 | + | Grind a flat spot on the large spool valve land with arrow pointed at it. It is not fussy, 1/4" to 3/8" wide is fine |
[[file:400boost01.jpg]] | [[file:400boost01.jpg]] | ||
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Method 2 to plug passage in case: You can remove the valve body and plug this hole shown in photo if pump removal is not going to happen. Perform this method or the method posted above. Both are not needed | Method 2 to plug passage in case: You can remove the valve body and plug this hole shown in photo if pump removal is not going to happen. Perform this method or the method posted above. Both are not needed | ||
| − | You can slip a 1/4 | + | You can slip a 1/4" check ball into the square hole and push it into the round passage at the base of this square hole. |
[[file:Block_rev_hole.jpg]] | [[file:Block_rev_hole.jpg]] | ||
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You can plug the hole with a brass dowel or a check ball. To use a check ball you will have to first drill the hole larger and then drive the check ball in place. | You can plug the hole with a brass dowel or a check ball. To use a check ball you will have to first drill the hole larger and then drive the check ball in place. | ||
| − | Drill the marked holes at .125 for street use. | + | Drill the marked holes at 0.125" (1/8") for street use. |
| − | For a heavy duty application : 3rd gear shift use .150 drill 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 0.150" (# 25 bit, 0.1495") drill and leave the 1-2 check ball out. Caution a 34 element sprag needs to used with the 1-2 check ball removed. |
[[file:T-400feed-holes.jpg]] | [[file:T-400feed-holes.jpg]] | ||
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This firms up the 2-3 shift. | This firms up the 2-3 shift. | ||
| − | Re-install the piston in the bore. DO NOT use a plastic piston, they break | + | Re-install the piston in the bore. DO NOT use a plastic piston, they break. |
[[file:100_2218-1.jpg]] | [[file:100_2218-1.jpg]] | ||
| − | = | + | =TH400 transmission rebuild tech:= |
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[[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 .150". | + | 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"). |
[[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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There are 3 choices here. | There are 3 choices here. | ||
| − | Solid teflon is on the left, then scarf cut teflon, then cast | + | Solid teflon is on the left, then scarf cut teflon, then cast iron. |
[[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 TH400's. | Cast iron is what most kits will contain, and what was used stock in most TH400's. | ||
| − | Scarf cut teflon was used on later model | + | Scarf cut teflon was used on later model TH400's. |
Solid teflon is used on 4L80's and is interchangeable. | Solid teflon is used on 4L80's and is interchangeable. | ||
I prefer solid teflon, although it is the most time consuming type. | I prefer solid teflon, although it is the most time consuming type. | ||
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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. | 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. | ||
| − | Notice I left one sealing ring off, 2nd from top groove. This groove | + | 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 Th400 will be covered in more depth in another section. |
[[File:Center_support_rings.jpg]] | [[File:Center_support_rings.jpg]] | ||
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You will install the rear thrust bearing into the case or the stock selective in the case with the stock thrust on the rear planet (using assembly gel, petroleum jelly, or grease to hold in place). | You will install the rear thrust bearing into the case or the stock selective in the case with the stock thrust on the rear planet (using assembly gel, petroleum jelly, or grease to hold in place). | ||
You will also install the low/reverse (rear) band. | You will also install the low/reverse (rear) band. | ||
| − | If required you install the fretting snap ring into the case. ATSG covers when this is necessary, most later model (71 | + | If required you install the fretting snap ring into the case. ATSG covers when this is necessary, most later model ('71-up?) trans have this. |
[[file:Casefretring.jpg]] | [[file:Casefretring.jpg]] | ||
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===Sprag design comparison=== | ===Sprag design comparison=== | ||
| − | This next picture shows a common roller clutch style drum and a roller clutch on the left, most TH400's will use this style drum, early units, pre-71 will have the smooth inner race style drum on the right. | + | This next picture shows a common roller clutch style drum and a roller clutch on the left, most TH400'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. |
[[file:Sprag-drum-compare.jpg]] | [[file:Sprag-drum-compare.jpg]] | ||
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===Spiro loc retainer=== | ===Spiro loc retainer=== | ||
| − | This is a pic of an upgrade for high | + | This is a pic of an upgrade for high RPM applications, it is a spiro lock type retainer instead of a regular snap ring. The regular snap rings will release due to centrifugal forces at high RPM. This fits on the direct drum plate that covers the sprag |
[[file:Spirolock.jpg]] | [[file:Spirolock.jpg]] | ||
| − | This part is a stock | + | This part is a stock 4L80E part available at a GM dealership. |
| − | A stock snap ring can also be tack welded to the retainer. | + | A stock snap ring can also be tack welded to the retainer. The TIG welding method with silicon bronze is best. Most DIY folks at home do not access to this method |
===Direct drum modification=== | ===Direct drum modification=== | ||
| − | In the direct drum, leave out the center lip seal. | + | In the direct drum, leave out the center lip seal. This is the "dual feed" modification you read about. |
[[file:Th400centerseal.jpg]] | [[file:Th400centerseal.jpg]] | ||
| − | Notice the circle around the check ball in the aluminum piston. | + | 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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===Drum installation=== | ===Drum installation=== | ||
| − | This is the intermediate clutch stack 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 luges here in the case are one of the weak points of a TH400, high line pressure, harsh shift calibration, and | + | This is the intermediate clutch stack 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 luges 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 2004R. Some performance vendors sell a brace that helps prevent case lug breakage. |
One of the keys is to keep line pressure under 250 psi if possible. | One of the keys is to keep line pressure under 250 psi if possible. | ||
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