Rebuilt 4L60E problems
I have rebuilt the 4L60E in my friend's 1994 Chevrolet C1500.
The transmission worked fine except it made a lot of noise in first gear. Disassembly showed that the input planetary thrust bearing came apart and its needle bearings went through and ruined the gears. The input drum also slid rearward (without that bearing there) and wore against the inside of reaction sun shell. The rest of the parts were fine (including the soft parts), but since it needed a new input drum I decided to perform a full rebuild. The replacement parts included: clutches, steels, seals, input planetary gearset, low roller clutch, input drum, Transgo 1994 valve body plate, steel check balls, Transgo shift kit, 1-2 shift solenoid, 3-2 shift solenoid, 3-4 check ball capsule.
The current and persistent problem:
P, R, N, 2, 1 ranges all work flawlessly. No slipping, good engine braking, perfect.
D and OD has perfect upshifts and downshifts but will not start from a stop. The engine will rev up and the truck will barely creep forward, but not as if it were in a gear. Once the truck is moving in 1, the shifter can be put in D or OD and it will upshift to 2nd, 3rd, and 4th like it should and downshift like it should on command, but will not go into 1st at a stop. If a downshift to 1st is commanded by flooring the gas pedal at low speed, the engine revs freely. Also, if accelerating in 1 at part throttle and the shifter is put into D for upshifting, the engine will rev freely for a moment while the 2-4 band engages.
At this point I have the transmission out and apart for the third time, not including the times I've had the valve body out and apart. I have CONFIRMED the following to be correct by subsequent disassembly, double/triple checks and consultation with experts and two GM manuals:
-Teflon seals on input shaft installed correctly.
-Pump assembly in good shape (72psi in D, 120 in reverse, pegs at WOT, but needle bounces rapidly +/-10psi).
-Sprag clutch like new and installed correctly.
-Shift kit installed correctly.
-Valve body assembled correctly, all valves move freely, check balls in proper places.
-All seals and pistons in input drum installed correctly and clutches have correct clearance.
-Have 12V to all solenoids, and transmission wiring plug is tight.
-Solenoids not replaced have correct resistance.
When I air-check the forward piston via the holes between the teflon seals on the input shaft, I need to cover the hole for the overrun clutch, and vise-versa. Shouldn't these fluid passages be separate? All the pistons have their check ball capsules in.
There is a small (1/8th inch long) mushroom shaped plug of some sort that looks like a rivet with a cylindrical shank and a hemisperical head. It came out and I don't know what it is or where it goes.
With key on and engine off, both shift solenoids have 12V from their red wires. The 2-3 solenoid's yellow wire to the ECM shows 70 ohms to ground (it is energized). However, the 1-2 solenoid's green wire to the ECM shows 33,000 ohms to ground. The resistance of that wire from the solenoid to the ECM plug is only 1 ohm (perfect). Thinking that the ECM was not grounding that wire for some reason, I swapped out the whole unit, but that yielded a goose egg. Then again, the 1-2 solenoid must be working because it needs to turn on for the 4th gear shift, which works fine.
I have rebuilt a handful of automatics before, but this is my first 4L60E. However, through this tribulation that's heading into its seventh week I have become VERY familiar with this transmission. I will greatly appreciate any insight.