Downhill slow towing will ruin your Ford 4R100 tranny!!!
Gauges needed!
After installing a tranny temp gauge (ford 4r100) it became clear to me why my first auto tranny failed, and why I almost destroyed my second tranny! My first tranny failed at only 10,000 miles. I figured just bad luck. Ford installed a rebuild at no charge to me. I installed a tranny gauge in this second 4r100.
On a trip,
going downhill, trailer in tow, in second gear(automatic) at about 15-20 miles/hour and with the exhaust brake on, all seemed well at first.
I had perfect control on this very steep, narrow, windy, no pullouts, Colorado back road, 10 mile long
shortcut. Just easin' on down the mountain. Seemed like a great setup.
Hah! Guess what! Tranny guage started to climb rapidly. At 210deg I was getting worried. At 230deg I knew I was in trouble. Then it went nuts, passing 250 deg and pegging beyond the numbers. It did this all within less than 1/2 mile!! (There was no place to pull over).
Anyway,after about another mile, finally got pulled over. The tranny smelled real bad. Got the oil (Mobil 1 syn) changed. Had an analysis done by blackstone labs on the burned oil. Conclusion "lots of carbon chunks but no metal, oil is ruined". I'm knocking on wood that the tranny will continue to survive.
That's also how I ruined the first tranny with no guages. DOWNHILL slow towing under 30 mph. Having a guage clued me in that I was just about to burn up my second tranny.
The torque converter unlocks under about 30 mph on these ford 4r100's, and this unlocked condition causes a RAPID rise in tranny fluid temps. Same condition as backing up a trailer. The torque converter is unlocked.
This is surely a design flaw and the only way to manage it is to use a tranny guage. Seems to only be a problem when towing a heavy load. Good Luck, watch those gauges and keep your power stroke above 30 mph