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I’m currently refreshing my 4L80E and noticed the original wave plate can now spin freely and isn’t engaging the lugs (all was fine on last rebuild). I bought a .060” th400 wave, and it still spun. A .090” direct steel doesn’t spin, but I don’t feel comfortable running it as it’s barely engaging the teeth (sideward pressure can still lodge it enough to concern me) My question is: What could be the cause of this, and what should be next step be here?
Also it’s a stock bonded piston, I’m just unsure as to whether or not this is typical. My assumption is that when the wave spun in the groove, it squished the piston enough to reduce the work surface height beyond spec. I can’t tell by looking at it, but I’ll grab another piston and go from there.
Original piston has been gone for about the last 6 months, no problems with direct piston in the direct drum (oem wave engages well and has “DIRECT” imprinted on it), and drum is original from the core (didn’t have this issue during last refresh). I put 10 miles on it after previous refresh, then all neutral. I’m not gonna get into specifics, but let’s just say this time around I’m gonna make reeal sure the boost valve snap ring is seated
Anyways, do you think I should just order up a new piston and go from there? I see no issues with the drum.
edit: I also really didn’t want to take the direct piston back out again and shove it in the fwd, I fxkn hate that little snap ring. If that’s what you meant by the fitment of direct piston
I just threw in the direct piston in the forward drum, and was happy with the piston height and clutch pack clearance. My new question being: can I run a direct piston in both the direct and forward drum without issue, as long as my clutch pack clearances are good to go? And if this is an okay practice, would I still use the forward piston springs+retainer with this combo?
The Direct Piston and the Forward Piston are Hydraulically divided into 2 separate Chambers.
A Inboard Chamber and an Outboard Chamber.
When we Dual-Feed the Direct Drum, we eliminate the Seal that separates the 2 Chambers of the Direct Piston.
The Forward Drum is usually left Stock...
as both Chambers have a slow flowing Bleed Orifice between the Chambers that soften the Shift into Drive from Park.
The Inboard Chamber of the Forward Piston is smaller than the Direct Piston.
As such they are not completely identical/ interchangeable.
If you install a Direct Piston into the Forward Drum, the Inboard Chamber will not be sealed/ separated from the Outboard Chamber.
Doing so is fine for Very High Stall-Speed Torque-Converters, Trans-Brake use, and or Off-Road/ Race use Only applications.
I do not recommend it for Stock-Type/ Lower Stall-Speed Torque-Converters, or Daily-Driver Vehicles.
I’m currently running extreme automatic’s reverse pattern transbrake valve body (boost valve shimmed to achieve ~180psi line pressure), and one of Jake’s converters spec’d for a ~3500 stall 900hp turbo 6.2L ls application. I have the direct dual fed (sealing ring left off center support, ~.050” bleed hole, and valve body does the rest). As for the forward drum, I have the center sleeve seal removed, which already firmed up the shift to drive. For my application, as it’s my personal vehicle, I don’t mind how hard it slams into gear as long as functionality is not altered. If I do run the direct piston in the forward drum, is there any other alterations needed to be made? Firstly, would I use the forward or direct spring+retainer? Also, if there is anything else needed in my application, I would greatly appreciate your input. Thanks again.
Sounds about right, my dial caliper is a tad off atm. Fortunately, the extra height of the direct piston is just what I need for my build. Thanks for the help again everyone.
the forward drum is ALWAYS "dual fed"
look at it and you will see
the middle seal on the fwd drum is just there to slow the apply rate of the piston...making the "garage shift" less agressive...it does this by sealing off the inner from outer chamber and making all of the apply oil between the two flow through an orifice in the drum
SO...the two chambers are connected...just via a little bit smaller hole that controls the apply rate of the piston. The intention was to keep it from "slamming" into drive.
Using the direct piston is fine and will just result in a slightly more firm shift from PRN to D as the fwd clutch engages.
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4L80E Forward Drum Question 
