Destroyed My Transmission

I recently destroyed the auto tranny (4R100) on my 2000 Ford F-550 Super Duty. I did something I was later told the tranny couldn’t handle. While towing my 5th wheel RV, at the top of a 10% downgrade, I did what many would do - put the tranny in 1st gear and headed down the 2-mile road. Even with an exhaust brake applied, the speed rose to 25mph. I used the service brakes and successfully arrived at the bottom. I later discovered, however, that the tranny reverse gear was no longer working. A knowledgeable mechanic advised me that the lower reverse clutches burned out (confirmed when the tranny was replaced). I was told the under these conditions (1st gear, steep grade down, heavy load), the tranny only applied 24 PSI line pressure to these clutches that caused the demise. Why doesn’t Ford advise not to do this? What should I have done at the top of the hill?

1st seems extreme. Would the result have been different in 2nd? No help i know but im curious

The general rule that truckers often use is to descend in whatever gear it took to ascend. First probably was too low. I’m not sure how Ford would advise against it - its sort of a complicated set of circumstances.

Two quotes from the Ford owner’s manual:

Concerning the automatic transmission “Use 1 (low) to provide maximum engine braking on steep downgrades.”

Concerning driving while you tow “Use a lower gear when towing up or down steep hills.”

This 10% grade had a 15 MPH speed limit. Under those conditions, 1st gear seems right to me.

Sounds to me like your take on it is reasonable. Maybe getting in touch with Ford is in order.

Of course, you don’t mention the mileage on the truck, the service history of the transmission, or the amount of heavy towing you’ve done. Perhaps it has something to do with heavy stress on a transmission that has already seen a lot of work and fluid in marginal condition? I.e. it might not be that it was this single event that killed the transmission.

Actually, with modern trucks, the rule has been amended. Now you are supposed to descend the hill in a gear or two lower than the one used to climb.

Based on that information, I might have done the same thing. However, how long was the steep grade? Was it short enough that you could have used the brakes without overheating them?

With such a low speed limit (15 MPH), I think you probably could have safely used the brakes.

Thanks for the observations. The hill distance was 2 miles, so I did use the brakes to keep the speed down.

Total truck mileage - 79,000. Two thirds has been towing the RV, which is at the truck capacity. ATF changed to synthetic at 21,000 miles, and again at 50,000 miles. Aftermarket transmission temp gauge has never shown excessive temps (although I wasn’t watching this gauge on the downhill ride).

When presented with the reverse shuddering problem (and nothing else), the knowledgeable mechanic diagnosed the issue with one question to me: “Did you recently go down a steep hill with a load in 1st gear?” His experience is that this transmission will fail under those circumstances. When dismantling the old tranny after replacement, there was no clutch material remaining on any of the lower reverse clutches.

At 10 years on the truck, I believe I have no recourse with Ford.

“Total truck mileage - 79,000. Two thirds has been towing the RV, which is at the truck capacity.”

Sounds to me, under these service conditions, you have little to complain about…Automatic transmissions don’t last forever, especially when being operated at or near their service limits. Maybe your next truck should be a Kenworth with manual gearboxes…

Well, perhaps.

However, while I didn’t use 1st gear down a steep hill until 79,000 miles, I’m advised that the transmission would have failed under those conditions with only 100 miles on it (24 PSI line pressure to lower reverse clutches apparently permits clutches to slip and burn up under those circumstances).

Ford might laugh at you w/ a 10yr old truck, true. But sometimes it makes me feel better to just let people know exactly what I think. If we’re all supposed to live under the delusion that consumers are the ones who are really in charge of the economy I figure I can at least be an active consumer. I normally get nothing of substance out of it, but I frequently tell companies where they have messed up and cost me time & money in the process.

Two thirds has been towing the RV, which is at the truck capacity.

Ah, that makes things kind of tricky. I am guessing you don’t weigh the truck and trailer on every trip, so there could be times when you exceed the truck’s capacity and don’t realize it.

Most tow vehicles have two capacities, gross vehicle weight capacity, and towing capacity. It is pretty easy to exceed one but not the other. Also, as an avid RVer, I can tell you that your trailer’s gross vehicle weight rating (GVWR) is an estimate of the weight of the loaded trailer. That number is often higher than the trailer’s actual weight, but not always. It is pretty easy to load a fifth wheel trailer to the point where it exceeds the GVWR, which might exceed your truck’s towing capacity.

It is always a good idea to leave a margin between the weight of the trailer and the tow vehicle’s towing capacity. Caddyman’s advice about the Kenworth isn’t too far off. If I wanted to tow something that was heavy enough to come close to the towing capacity of a Ford F-550, I would consider a semi. Since you will be pulling an RV, a sleeper cab shouldn’t be necessary. A used Freightliner with a day cab would be my preference. Kenworths are expensive, and Freightliners are cheaper to buy and cheaper to repair.

While in 2000, Ford subsequently offered a 30,000 lb GCWR F550 (as an option), my F550 has a 26,000 lb GCWR. Knowing I would be towing heavy, I put synthetic fluid into the rear differential (as did the option), and used synthetic ATF in the tranny. Total weight of my package (loaded truck and RV) is 27,000, so I am exceeding the GCWR by 1,000 lbs. I’ve accepted this. There is little difference between the 26K and 30K versions, and I’ve taken steps to mitigate the difference. Acknowledging that the auto tranny in the Super Duty trucks has been their weak point, I monitored tranny temp while towing - never seeing excessive temps (although this event was certain to have been problematic).

A business-class tractor would not have worked out for me 10 years ago. Maybe the next truck.

I’m most disappointed that the stock tranny has a flaw that some folks know about, but is not apparently acknowledged by Ford.

My end result, however, is an F550 with a custom transmission that doesn’t have the weaknesses of the stock 4R100.

The way I look at it is that the transmission is 11 years old and has seen a lot of severe towing duty. It’s likely the descent is not what killed it and it’s simply the victim of time and wear.

As to design glitches, every automatic transmission made has them to one degree or the other.

…I am exceeding the GCWR by 1,000 lbs… There is little difference between the 26K and 30K versions, and I’ve taken steps to mitigate the difference.

Those words are probably etched on someone’s tombstone somewhere, right next to the tombstone that reads “Look, Ma, no hands!!!”

Regarding the transmission temperature, keep in mind that what you really monitored was the temperature of the temperature sensor. Other components of your transmission away from the sensor could have easily overheated without ever showing up on that gauge. I have pushed some tow vehicles pretty hard, and although the temperature gauge never moved, I could feel excess heat from the engine compartment when I checked the fluids at fuel stops.

Even once you get the custom transmission, I strongly recommend you either get an appropriate tow vehicle for this RV or get an appropriate RV for this tow vehicle.

Why not use the brakes in conjunction with a lower gear(not the lowest?).

If your brakes cannot handle the load they are undersized for the application…