Re: Torque converter
Any time you are at a steady speed over 32 MPH, the TCC will try to lock. As soon as you hit 2nd gear, the TCC passage is pressurized with oil and the TCC solenoid can now block flow and lock up the converter clutch whenever it's energized by the ecm. Your brake pedal can break this circuit. That's why you can "tap" the brake and the TCC unlocks and the rpms go up 200 to 300 rpm.
Tooky is right. It's a load issue. What's happening is the clutch in the converter is wearing out. When you are in 3rd, your RPMs are higher, your overruns are locked in and the line pressure is boosted slightly. This compensated for the worn out converter clutch.
When you go into 4th, the 4th servo pushes on the band and grabs the reverse drum which slams the sun gear shell, the rear sun gear and slams them stopped. The overruns release so the sprag can go into "overrun" condition. Pressure is reduced. The shift accumulator valve gets hit(this is the valve that determines shift feel) and it pulses the NC switch and opens it temporarily. This unlocks the converter for just a second so you don't put such a large strain on the engine and trans so the converter can absorb some of this energy as a cushion. Then it's time for clutch to reengage. This is when you guys are gettig the chattering.
You can get by for a little longer possibly if you have a .470" TV boost valve. This means you can go up to .500" TV boost valve. This will boost pressure. While you have this boost valve out, modify the PR valve so you get lube at Lockup. There's instructions all over how to do this. Normally this is only necessary in the syclones. The Typhoons tend to already have the PR valve update as done by GM in 1992.
So two options. Try the boost valve with lubegard and type F fluid.
If this don't work, it's time to replace the converter and freshen up the trans(new clutches).
Oh, BTW, if you are going 40 and you are in OD, this means your TV cable is set too soft or worn out. Minimum OD is 44 mph is stock 700 syty setup. This means your pressures are a little lower than they should be compounding the problem.
I was done but thought I would add a little more so it makes sense.
Imagine you are in a steady state. Cruising along at 35 MPH in 3rd with the TCC locked. You start to go up a hill. You are not pressing harder on the pedal. The weight of the vehicle loads up on the engine through the trans as gravity tries to push you backward. The load on the engine increases but your trans pressure is staying the same. The TCC clutch is now taking a pounding (you feel this as a chatter as it slips) and ECM cuts off the internal ecm ground and makes the TCC clutch unlock. Ground level off. Road speed comes back up to about 33 or 34 MPH and it's time to relock. ECM regrounds the TCC solenoid and lockup is commanded. Your worn clutch is trying but you get a "chatter".
That's a little of GM TCC logic.
