Blocking the 3rd gear Accumulator on a 4L80E, Unbolt the 3rd/4th Accumulator housing from the Valve Body. (The Valve body has to be removed)
Remove both Accumulator Pistons, The one without a guide pin is the 3rd gear Accumulator, The Hole near the bottom of the big bore is what needs to be blocked. (arrow).
Using a 5/16-18 tap, Carefully tap the hole deep enough so the Set screw sits below flush, The Hole is at an angle....Try to keep the tap at that angle.
Test fit the set screw so you know it's seating below flush, You can make fun of the Gold Plated set screw if you want, I bought 2 boxes full of them from an Audio install shop that was going out of business.
You can Block the 4th Accumulator if you like (I generally don't unless a high stall converter is being used), It's the exact same method, Just remove the guide pin to tap the hole.
