This 700R4 tranny has shifted too soon into overdrive the entire time I've had this car (1986 5.0 liter) and is now starting to slip in and out of overdrive while cruising highway speeds. I have tried to adjust the shift cable only to make it worse. My plan is to get this tranny rebuilt soon. Someone suggested the shifting is controlled by an EPROM (no vacuum connected to it), if so I would like to pursue this while the rebuild is taking place. And if this is the case is this something I may be able to tackle myself? Thanks in advance.

 

First of all 700R4's are not shifted by the ECM. The only transmission function controlled by the ECM is TCC lockup, which could be confused as the shift into overdrive when it locks up. Fooling around with the shift cable (I assume you are talking about the TV cable) will get you a burnt up trans. There is only one correct adjustment & that is fully extended with the throttle wide open, since it is there to synch throttle position with line pressure in the trans. You can adjust the shift points by changing the weights & springs on the governor. There are kits available to do this.

 

It does act like the transmission lockup (OD) is what the trouble is. If this is controlled by the ECM what options do I have for selecting more duration for this lockup to occur. And it now seems to be unlocking occasionally while cruising, any ideas about this?