Hey everyone, i was just hoping to get some advice from everyones experiences with the 6.2 and 400 tranny. Im running a two tank system with a beefed up IP and a vegthem mega and all seems to be well for the time being. Today i started her up, drove out the driveway and was experiencing a lot of strange shifting patterns. It was shifting at about 4 or 5 k and really rough and would lurch forward and when i would slow down the least bit it would down-shift. I parked, took a hike and came back about two hours later and on the drive home it didnt seem to be acting like this at all. Any ideas? also i have about 205 k on my engine, im very paranoid about anything happening because i have no garage to do a rebuild, i was just hoping to get any general advice or tips about engine maintenance or things i should be prepared for. Thanks

The TH400 has two forms of shifting control other than the gear selector.

One is the vacuum modulator (for part throttle shifting and the second is an electric switch (for kickdown).

If the vacuum source for the vacuum modulator isn't strong enough or is missing completely, the transmission will only shift at high engine speeds (no vacuum signal) or higher than normal speeds (to low of a vacuum signal). Modulator valves can fail too.

If the switch for the kickdown is stuck closed, power (vehicle voltage)is applied to the kickdown selenoid. The transmission only shifts up to the next gear at peak engine RPM.

Vacuum to operate the modulator is produced by a vacuum pump mounted at the rear top of the engine. It is then routed through a vacuum regulator valve mounted on the fuel injection pump. A faulty vacuum pump or leaking vacuum lines will cause problems as well as a defective vacuum regulator valve. With the engine idling, you want a strong vacuum signal at the modulator (located toward the front of the transmission on the passenger side near where the pan bolts on). The factory ones are round and about 3 1/2 inches in diameter.

The electric kickdown switch should be located above the throttle pedal. The wire at the transmission plugs into the drivers side near the rear of the transmission. The only time the wire should have vehicle voltage is at full throttle. It is also possible that the kickdown selenoid is stuck. That is accessed by removing the transmission pan.