I have a 1986 Trans Am with a 305 TPI motor and a 700r4 transmission, both of which are stock. After pulling the transmission and redoing the torque converter seal, I did a transmission service and all is well except for a surging while coasting in overdrive and 3rd gear. The issue is a surge of 400-600rpm between 25 and 50 mph. From other information I can gather, the issue sounds like it's most likely the torque converter slipping in and out of lockup. I do have the 4-prong connector plugged in and it did click, as well as the other connector on the transmission. The TV cable is properly adjusted from what I can tell, and the transmission fluid it at the proper level. What could be my issue?

 

The lockup can cause weird problems & they do fail. One of the symptoms is in & out of lockup. Another is that it will stay on permanently.

 

What I'm not understanding is why would it be doing this and how do I stop it? It's not an aftermarket lockup kit, everything is factory from what I can tell. So why would it be surging in and out of lockup like that?

 

U have to have a new lockup installed probably at a tranny shop.

 

The THM700-R4 uses the Cooler Charge Circuit to hold the Torque-Converter Lock-Up Disc off.
This is of course when we do not want the TC Locked.

Something as a simple restriction (or drop in Pressure) of the Cooler Charge Circuit, can cause unwanted Lock-up (intermittent or constant).
Less than the required pressure, will result in the Lock-Up Disc not being held off.