GM and aftermarket companies have produced affective solutions for most long term durability issues that the 4L60 transmission series has encountered. However one main aspect has been left behind…….
The 3-4 clutch ! Until now the fix has been to try every color clutch material that crayola has to offer. Bottom line is even the most reputable builders have their hands tied. Knowing well in advance that 3-4 clutch failure will be the death of even there best built transmission. There’s been nothing that anyone could do about it – until now….
Starting at the bottom pressure plate. They were produced from soft powdered metal, and flawed by the design of receiving all apply pressure through 5 small spots on the whole plate. Pressure from the piston below cause that plate to flex/distort and only put full apply pressure at those 5 spots. Creating problems right from the start. With increased line pressure the problem only gets worse.
As we work our way up into the clutch pack, in factory form they have 6 frictions, 5 steels and another powdered metal top pressure plate all held into the aluminum drum with a snapring.
The lack of rigidity and the narrow width of the clutches, whether it be the frictions or steels, soft top and bottom pressure plates accompanied by the flex at the drums snapring groove, cause the entire clutch pack to cone / bow creating a recipe for disaster. It doesn’t take long to start and once it does it has a domino type effect (starts off as a 2-3 flare) and in short order you’ve lost all 3rd and 4th gears. The modifications of adding more frictions and steels has long been exhausted by the same repeat failures. To add more clutches you’ve made everything thinner to accommodate the additional clutches. The negatives out way the gains as the thinner clutches only make it harder to dissipate the heat. Until now, anyone with a high powered 4l60 vehicle has usually had many 3-4 clutch failures by even the best transmission builders. Causing them to be very costly and in turn making them afraid to drive there vehicles to their full potential. Not anymore.
Gm had there chance to make things right, they started with the 4l60, then the E model, came out with a 4l65e and finished by giving us a 4l70e. Along the way they made some great changes but almost nothing to prevent 3-4 clutch failure. We’ve given it the name 4L79 because it’s as far as you can take this transmission before it’s time to step up to a 4l80e.
Starting with a wider bottom pressure plate thats been cut from rigid material to avoid the flexing, from there we’ve machined the input housing to allow the use of custom larger outside diameter steels. Machining of the drum also consists of milling the top flat to achieve more clutch capacity, then threading the outside of the drum. A top cap / pressure plate is then machined from 6061 aluminum billets and threaded to match the drum. Using the custom steels and supplied EXIDY high energy frictions the 3-4 clutch now has 185% friction surface area over a stock 4l60e clutch stack up. Not only does it have that much more friction surface area, but that much more steel surface area as well. Further aiding in heat dissipation. The billet cap is threaded to the drum tying both drum and cap together making the pressure plate surface and drum rigid, eliminating the bowing and coning. The threaded cap is locked into place to prevent spinoff using 5 set screws.- they do not hold the cap down or any pressure- strictly for retaining purposes. By making the end cap aluminum, it transfers the heat better than steel, the top of the clutch packs heat then goes directly into the cap and then into the input housing itself shedding the heat.
We also offer a 4L78 input housing kit which consists of a custom machined input housing with billet top cap. Also achieved is extra clutch stack up height. All while still utilizing stock style frictions and steels.
Finally we offer our 4L75 drum kit. This kit is a drum that’s machined and uses the same larger custom EXIDY frictions and custom steels. However they are still retained by a top snapring like the OEM drum. Kit comes with drum, thick bottom pressure plate, 7 frictions, 6 steels, and another thick top pressure plate. Also included are 5 new load release springs.
Simply put – Seeing Is Believing, just take a look at the parts and compare for yourself.
4L79, 4L78 and 4L75 are patent pending