Hey guys, first post here. I'm usually more active in the Powerstroke forums, since my half ton has been spectacular.

Bit of backstory. 2005 5.4, 4wd, currently approaching 240K miles. Like I said, it's been a fantastic truck. I did plugs and coils when I bought it 60K miles ago, and everything else was preventative maintenance until 200K miles, when the original transmission went out all at once. Pulled into a parking spot and it was fine, pulling out and every gear slipped like crazy. Can't fault it for that, it's been worked hard and any automatic transmission that makes it to 200k with lots of heavy towing is OK in my book. I work in the salvage industry, and know just about every junkyard owner in the state, so I got a great deal on a low mileage (90K) used transmission that I swapped in, and it's been good until tonight.

Went to pass someone on the highway, and with my foot to the floor at about 40 the truck downshifted to second as you'd expect. Shifted into third pretty hard, but not hard enough to cause tremendous concern. Fourth and overdrive were fine as always. 20 miles later, the trans fault light came on with the standard flashing overdrive light. Pulled the codes on my edge (running stock tune, I just use it as a monitor), got P0731 and P0732 for incorrect ratios in first and second. Truck was driving fine, so I kept it moving. Came to a stop sign, pulled out, and the truck had no power. Again, foot to the floor and it wasn't slipping, just accelerating like I was barely giving it any gas. After about 15 it caught and actually broke the tires loose, and I made it home.

Some experimentation has revealed that with the gear selector in reverse, 1st, and 2nd, it might as well be in park. On a grade with the nose pointed up a hill, it will roll backwards in neutral, the torque converter holds it steady in drive, but anything else and the transmission is completely locked, and you can rev the motor all day long with no impact on what the transmission does. Shut the truck off and tried driving it again and now it won't shift into overdrive. I can hear and feel something moving in the transmission when shifting into reverse, and in park and neutral I can hear a RPM dependent whine from the transmission. Added a quart of transmission fluid just for S&G's, no difference.

I consider myself very mechanically competent, but automatic transmissions are black magic witchcraft to me. In my experience though, things don't fail in this manner. I'm trying to reason my way through what could cause reverse and a manual selection of 1 and 2 to lock things up but in drive it at least moves, and the fact that it doesn't slip in drive but won't increase engine speed until it grabs strikes me as odd. I read a post from a while back about someone who had the lock for the reverse gear clutches fail with very similar symptoms a while back, but I don't know enough about autos to know if that sounds reasonable.

Any advice would be welcomed. I really don't want to put another transmission in the truck with this kind of mileage, but my other vehicles are in even worse shape, so I'm going to have to make a decision eventually. Thanks in advance!

 

Does this help?

https://www.obd-codes.com/p0731

 

I've never heard of a lock for a reverse gear clutch. It sounds like a part that someone who knows nothing about transmissions made up. That's the problem with internet diagnosis. A good writer can make it sound like they know what they are talking about.

I think you're going to have to do what you don't want to do. The reverse clutch is sticking on. Usually, that happens because the clutch was overheated and warped and can no longer release correctly.

 

This is why I would never buy a used transmission. You are buying someone else's wear and tear. Just as much expense and labor for installation. No warranty.

You will need another transmission. Consider remanufactured with a warranty, or a rebuild with a warranty.

 

I can swap a transmission in 3 hours flat, so the labor isn't an issue. And there's not a chance in hell that I'm paying the same thing that the truck is worth for a new transmission at 240k miles. If there truck were in better shape and newer I would agree with you, but dropping several stacks on something this tired just doesn't make any financial sense.

 

How in the world does a reverse clutch overheat? I'm not doubting you, it just seems like you'd have to beat the snot out of reverse to blow the clutch. Any way this can be replaced by itself?

 

An update for those interested. I spent more time today playing with the selector, in first gear it might as well have been in park. No movement, not responsive to throttle input. Second I found would creep a little bit as the tachometer climbed, so I did what any self-respecting truck owner would do and pinned it. Transmission clunked, the tires spun, and now I'm back to having a fully functional transmission.

Obviously something is broken, and eventually the issue will come back, but this gives me hope that it's something that can be repaired rather than replacing the whole transmission. Shift solenoids maybe?

 

How confident are you in your abilities? As for myself, tearing down and rebuilding a transmission is not in my skill set. You can buy the rebuild kit, and do it at home if you have the know how. The kits are commonly available from Summit Racing, Rock Auto, Amazon.com, and just about every auto parts store across the country. Remanufactured transmissions are also readily available, and they are sold with warranties.

Only you can determine what your budget is, and whether it's worth it to you or not. Only the math in your head will make sense to you, when it comes to what your truck is worth, and how much you're willing to spend on it. You already know from this experience, how much it's worth or not worth to keep your truck running, vs buying a new truck.

 

You could have had cross leakage which partially applied the reverse clutch. If there is enough pressure to make the friction materials touch they will get VERY hot VERY quickly. If they get hot enough they warp and bind in the clutch. This makes the clutch stick on.

Another common way the reverse clutch overheats often happens after snow storms. The vehicle gets stuck and they rock it back and forth to get it unstuck. That can also overheat and destroy the reverse clutch.

 

If you're on a strict budget and don't mind doing the labor then head to a local pull a part. Drop the pan and look at the fluid before you pull. You can walk out the door around here for $130 with a transmission that has a 30 day replacement warranty.