The TH350 or 400 (don't know which it has) automatic transmission on my 1980 Corvette went out, so I will be ordering a 700R4 soon. However, one of these days I will be upgrading the engine to a 400+ c.i. small block.

My question is how do automatics know when to shift? I assume it is "programmed" into the transmission, rather than the transmission simply being able to measure airflow or something to determine when to shift. If it is programmed in, won't I have to have the transmission pulled and reprogrammed once I upgrade my engine? What are all the variable that are actually programmed into a transmission?

Thanks for the help.

 

The non electric versions which didn't happen until '93 I believe for the electric ones, have a tv cable that controls line pressure that controls shift points. Also I believe the governor plays a role as well. Then there is the 46L0E which I assume is totally computerized.

 

Actually, the TH350 doesn't use a TV valve. It uses a modulator hooked to manifold vaccuum to accomplish that. The cable that attaches to the throttle body is simply a kickdown valve (actually acts more like a "switch [ON/OFF]" than a "valve [PROGRESSIVE]") to tell it to drop a gear when you floor it.

And on 700s, the TV valve doesn't control when the transmission shifts. It only controls the pressure so that at higher RPMs it has higher pressure in order to hold the clutch packs against the increased torque, quicken the shifts, etc.. What controls the actuale shift points is known as a governer. It's a gear driven centrifugal valve..er.. it has weights that are held closed with springs. As it spins faster the weights fly out and opens a valve that causes the next shift. You can change the shift points by varying the spring strengths or weights on the governer.