I have a 1995 Ford F150 with a 5.0L EFI engine, automatic transmission with overdrive, and 205,000 miles. The overdrive button is on the gearshift and I always leave it on. When cruising a 60MPH the transmission will randomly drop out of overdrive into 3rd and even 2nd gear. Sometimes while cruising at lower speeds the transmission will randomly drop from 3rd to 2nd. Taking my foot off the accelerator momentarily causes it to shift back to the proper gear. This occurs more frequently during the summer months. The transmission was rebuilt at 134,749 miles and the throttle position sensor was changed at 197,558 miles. My mechanic now thinks the torque converter is failing. What do you think is the problem?
A faulty torque converter would not cause the transmission to be downshifting like that. The very first thing to check is to scan it and monitor the TPS. A faulty TPS would cause the downshifting problems.
transman
An engine misfiring under load will also make a vehicle downshift like that. I had a van that started shifting up and down on hills it had never downshifted on before and it stopped doing it when I changed the plugs.
The TPS is not setting any codes. I had the Trans fluid and filter changed. The pan and the filter were pretty clean, minimal metal shavings. Now the down shifting is occurring less frequently. Could there be a intermittent electrical connection?
Just because it didnt set a code doesnt mean that its not intermittantly spiking. It could be electrical. Intermittants are a PIA to find.
transman
I thought the button in the “on” mode cancelled the overdrive gear. ‘Overdrive’ I see by many posts is a mystery to some, it should be used only on flat highway at speed and not towing or without a heavy load. OD drops rpm down but keeps the speed up.