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Old 09-22-2017, 08:29 PM   #164
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Join Date: May 2009
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Posts: 6,255
Re: 4L80E & TH400 Tech.

Intermediate Clutch Tech continued....

Intermediate Clutch Pistons
There are 3 different styles of pistons used in TH400's & 4L80E's.

The Stamped Steel "Multi-Piece" piston was used only in TH400 & TH375 units throughout the 70's & 80's as a cost cutting measure, Using a plastic lower retainer & 3 return springs. (Though you can run 6)
DO NOT use this piston in any HP build.....Or ANY build if you have a choice. Not only does it have a very thin work surface, They can also come apart & burn up the intermediate frictions!

Up next is the Aluminum TH400 Piston, Largest work surface of any production piston. Has a higher "Installed" height than a 4L80E Piston allowing you to set a fullsize Wave Plate OR a Flat Steel directly on the Piston. Has 12 return spring pockets. Most production TH400 only used 3 of them.

Last up is the 4L80E piston. Very similar to the TH400 version.....Albeit 2 important differences.
1. The Counter Bore is larger to allow use of a Spring Steel Wave Plate, The Wave has teeth that center it on the Counter Bore.
2. Has a shorter Installed Height to make the "Crests" in the Wave the same height as a Aluminum TH400 Piston.

I prefer the TH400 Piston because I prefer 3 Friction Intermediate set-up's......It takes up some of the height/distance when building a 4L80E. It's a absolute MUST when not running a Wave/Cushion Plate in the Intermediate Clutch!!!!

The 4L80E piston is a decent piece but as I stated......You HAVE to run the 4L80E Wave Plate, If you don't.....The first Steel/TH400 Wave will set on the Case Lugs NOT the Piston & cause the steels to wear on the case & put aluminum debris in your unit.
The Piston will also have to move about .040" before making contact making whatever clearance you measured incorrect.

The 4L80E Wave Plate is the most effective at cushioning the 1-2 shift.

The TH400 Wave Plate allows a little more of a crisp 1-2....But not shock the Intermediate Sprag to bad.

Unless your running a Aluminum Direct Drum with a 36 Element Sprag or a "Fly Weight Car".....I DO NOT under any other circumstances recommend omitting the Wave/s altogether!

I recommend running 12 return spring in all builds, This allows more pressure to build before the piston starts to move improving 1-2 shift feel. If building a 4L80E....Use the original springs, If building a TH400 CK Performance sells spring kits.
Running all the springs also makes 2-1 & 3-1 downshifts "Cleaner"

Stamped Steel Piston

Failed Stamped Steel Piston

4L80E Piston(left) & a TH400 Piston(right)

4L80E Wave(left) & a TH400 Wave(Right)
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