47RE O/D and T/C lockup

[turbobill]

I have a '97 12V with the 47RE automatic (all stock with 125K on the clock).

Under normal conditions the truck will shift into overdrive at 44mph (light load) and the torque converter clutch locks up immediately after the shift. If I lock out O/D, the TCC will lock at about 36mph while the transmission is in direct gear.

On a cold morning several years ago I noticed that O/D was not engaging until 56mph (no matter the throttle position). As soon as the transmission went into O/D, the TCC locked immediately after. Also in direct gear the TCC no longer engaged until 56mph. It drops out of O/D at 51MPH. It seemed to me that the transmission was in some kind of default mode. After awhile, transmission operation returned to normal.

A couple of years ago this problem came back and it has been a permanent change. The only abnormality I noticed with the scan tool hooked up is that "expected governance pressure" and "actual governance pressure" were different. The later being about 80% of the former. I was able to cycle all selenoids and the transmission temperature readout is normal.

Everything else in the truck works as it should. Has anyone else had this problem and if so what was the problem. Any ideas from the experts?

Thanks!

 

[Ozymandias]

Below a certain temperature the transmission does not shift into OD nor does it use the TC clutch until the Trans is warmed up somewhat.

 

[turbobill]

Below a certain temperature the transmission does not shift into OD nor does it use the TC clutch until the Trans is warmed up somewhat.

With the transmission up to operating temperature the problem is still there. The temperature sensor is working normally according to the readout on the scan tool.

 

[Ozymandias]

I guess your transmission fluid isn't 30 years old yes.
Because then only this difference in demanded and actual line pressure seems weird.
TC cable return spring is there?

 

[BigPapa]

 

[turbobill]

I guess your transmission fluid isn't 30 years old yes.
Because then only this difference in demanded and actual line pressure seems weird.
TC cable return spring is there?

My buddy who owned a transmission shop was reading the scan tool as I drove. He had no explanation either for the difference in the governor pressures. Transmission shifts 1-3 normally. Fluid is new after a flush, filter and deep pan replacement.

 

[turbobill]

View attachment 136667

TCC only locks up at 56MPH, whether or not I lock out overdrive. As I only use the truck in the warmer months, the battery and transmission are well above the temperatures to inhibit TCC operation due to cold. And the 3-4 shift always occurs at 56mph regardless of throttle position, kind of like some sort of default setting.

 

[turbobill]

To anyone faced with a similar problem or who might be interested, I found the problem completely by accident during some maintenance last March. While replacing the batteries, fuel filter and rocker arm cover gaskets, I noticed some of the throttle linkage going to the back side o the pump was rusty looking and decided to clean it up. As I was taking it all apart, some of it was very stiff, especially the portion that operated the TPS. I freed up and lubricated all of the linkage and cleaned and painted the rusty parts. About a month later when I started using the truck for the summer, operation of O/D and the TCC was back to normal.

Even though the scan tool had indicated approximate throttle position as being correct, apparently it was not and the incorrect position caused by the sticking TPS linkage was enough to trigger a default mode.