4L60E Hydraulic Powerflow 

Thank you for the kind words!

There are a lot of recipes that builders use in this transmission. I know a lot of builders that block the 3-4 accumulator for better shift feel. I usually don’t mess with it, but I still think it’s a fine modification. Slipping fourth isn’t really a common issue as far as I’m aware. I know many also use the wide band. I’ve used it with great success as well, but now I stick with the borg warner band. I used to use the zpack 3-4, but I’ve went back to the borg frictions. The 3-4 doesn’t fail because of poor friction issues, but for pressure loss. Changing the frictions and steels won’t fix the issue without addressing the leaks. I found some weird 3-4 shifts with the zpack that were cured by going back to oe frictions. Of course, this is all personal preference. If what others do works for them, who am I to say their doing it wrong?

Steady states are usually zero. Normal adapts are usually within a few psi of zero, plus or minus

Hi Larry, With most 4L60e's, the 1/2 accumulator, the spring goes in first, then the piston. So you just see the piston when you remove the accumulator housing and the spring lives behind it. The early 4L60e's (1993 and 1994) had the 1/2 accumulator with the piston in first then the spring. With the 3/4 accumulator, the piston goes in first, then the spring. That is the one in the transmission case. With the forward accumulator, the piston goes in first, then the spring. That is in the valve body. Some shift kits have you alter the orientation of the 1/2 and 3/4 accumulator pistons, but if you are putting it back to stock, it should be as I mentioned above.

I would check a few things. 1) use a scan tool to verify that 4th is being commanded. If not, maybe the computer thinks it’s in manual third. 2. If it is commanding fourth, drill and tap a pressure tap fitting on the servo cover and check to see if pressure is getting to the servo piston in forth. If it is, then the servo doesn’t have enough travel to apply the band. If there is no pressure, yet there is a command, it could be a leak in the 4th circuit, gasket covering a spacer plate hole, or a shift valve that didn’t move.