Originally Posted By: JiL
Making gradual progress:
So far unable to locate just the stiffer version of Intermediate and Direct springs without having to buy a kit with duplicate parts
The stock intermediate spring retainer will not hold up to high rate springs, I have seen them fail with stock springs, IF you have access to a TH400 Retainer....You can use it & buy the springs separate,
HERE
High Rate direct springs "MAY" be able to be used on your stock spring retainer......Due to manufacturing variations in the Springs, Top retainer, & Bottom retainer, It can turn into a challenging endeavor trying to fit the ID of the springs into the top & bottom registers.
IF you have access to a TH400 Direct/Forward Top Retainer....Things will be easier(You will only have to modify the Bottom retainer if modifications are necessary)
Separate direct high rate springs
HERE
Let's address the shortcomings of production 4L80E Direct Pistons (This also applies to the Forward Piston).....
'91-'96 Aluminum Pistons should NEVER be used in a high performance application, They can break when subjected to higher than stock line pressure. Has a thin "Work Surface" that is undesirable for maximum clamping of the clutch.
'97-Current Bonded Steel pistons do not have breakage issues, But have the same thin work surface issue.
A Aluminum TH400 Direct Piston along with matching retainer is the BEST combination to use(Outside of a Billet Piston) in a performance 4L80E, Has DEEP spring pockets, Wide work surface, And will NOT break.
**A TH400 Forward/Direct Piston can be used in the 4L80E Forward Drum IF the press in center bonded lip seal is removed, TH400 forward & direct pistons have different "Work Surface" heights from each other.....
Using a TH400 Forward/Direct Piston in a 4L80E Forward Drum WILL require machining to fit a Wave & all 5 Frictions. The Forward Clutch is less important than the Direct as far as maximum clamping being needed, Just information for you.
Enough of my rambling.....
In the end I suggest buying the kit's for the Intermediate & Direct Clutch & move on, But it's your build & money.
4L80E Direct/Forward Retainer picture, As you can see the spring is retained by a stamped boss on the top & Tap on the bottom, They are a very tight fit with a stock spring.