I just shoveled the engine back into a 2010 F450 after a complete rebuild. I didn't drive the truck much prior to the rebuild, as it had a cracked piston and I didn't want to chance grenading the block, but the trans seemed OK, and had no codes prior to purchase (the engine, on the other hand was loaded with codes.

Anyhow, first test drive after installing the engine was great until I turned around to head back to the shop. After slowing and stopping, the engine seemed to rev high and the truck lost power to the wheels, almost feeling like it was in neutral. I stopped, put the truck in park, then started off again, drove great until it didn't, then all of a sudden it started shifting and grabbing gears perfectly. At first I thought it was only in the 4-5 range that it was doing it, but after more observation it looks like it happens throughout the range (never notice a problem in reverse, though). It never gets jerky or shudders, and doesn't necessarily correlate with operating temperature. It's just sometimes okay and sometimes not. It seems to happen mostly after decelerating or stopping. Fluid is clear and bright, no trace of any burned smell.

I'm going to disconnect the PTO pilot line and put a line pressure gauge on it today and see what happens, probably going to drop the pan and have a look before I do much more troubleshooting. The outside of the trans is cleaner than the rest of the truck, and it has a reman tag on it, so I don't know if this is a carryover problem, and the previous owner said he never had any trans problems (for what it's worth) though he didn't own the truck long (it was more truck than he needed and the engine blew while he had it listed for sale).

Curious what else I need to be looking at, or what conditions to look for? I have both Autoenginuity and Forscan. I'm just getting to know Forscan, but it looks like it can see more of what's going on in the trans than AE.

***Edit**** TCM and PCM are currently showing no codes

 

You should check for low transmission fluid level.

 

I should have clarified that I checked the fluid level both before and after the issue started. The fluid is clear and bright, and full to the max level with the truck warmed up.

I checked line pressure this morning. It's right around 90-95 psi in park and drive, and about 115 in reverse.

 

Are you checking the level with the engine running?

 

Yes, Sir. Engine is running when checking. Just dropped the pan and pulled the filter. The pan is pristine, though I'm sure the filter hasn't been changed in some time. No "material" in the pan, just what i would consider a normal amount of fines on the magnet.

I did notice the following (if it's of any consequence) the solenoid coils and spools all slide pretty loosely in their respective ports, as does the range select spool. Both the range select spool and the low/revers clutch select solenoid seem to have a bit of darker fluid dripping from the non-acutator ends. Perhaps failing o-rings? I've yet to look up a good breakdown of the valve body to understand it better. Perhaps we're just up against a clogged pan filter?

 

I spent a little bit of time on this yesterday. Hooked up a line pressure gauge and checked it both cold and at operating temperature. Pressures seemed pretty consistent
P= 90 - 95psi
R= 115-120 psi
D, 3, 2, 1 = 90-95psi

I drained the pan and inspected, changed the filter, 8.5ish quarts of Mercon LV back in. The only thing that seemed odd to me was the solenoid spools and the manual shift spool seemed very loose in their respective ports and had a bit darker fluid dripping from a couple as described above. On the test drive, the truck drove flawlessly for about 20 minutes, then back to revving high and losing power to the wheels (I guess we'll call that a slip). Trans temp (from serial data) at when that started was ~144*F. Since I was on backroads, I could pay much closer attention to the computer. It appears that once the trans begins slipping, it continues across all forward gears. On an empty lot, noted no problems in reverse. Parked the truck and PTO engaged just fine (indicating line pressure is at or above 95). Back on the road, if you push it to a "sweet spot" where it catches a gear it drives fine until you cause it to try to shift. After cooling off, drives great again until hot, then anomalies in all forward gears.

I haven't been able to find a true hydraulic schematic of the 5R110, but at this point it seems to me that when the temp is high, the reduced viscosity is allowing fluid to bypass either the manual shift spool or the solenoid spools. Not seeing a lot of supporting information out there, but is it possible that the valve body itself is beyond its tolerances and needs replacement? It seems with such a low viscosity fluid and metal to metal valve fitment that the valve to body clearances would be super-critical. At resting temperature they are (by feel) seemingly loose, I can only imagine they don't improve with increased temperature. Could it be time for a valve body?

Even with that, though, no codes?

I guess my next step is to make up a longer hose and take it for a test drive with a line pressure gauge installed.

 

After messing with this thing on and off for several days (gauges, forscan, tees, fittings, etc) I think we've finally run it to ground. The PTO is activated by line pressure which is isolated by a solenoid. I had tested the solenoid previously using a hand pump, done road tests with line pressure gauges installed, drove around monitoring forscan, and couldn't find an issue.

Today we found that when the solenoid gets hot, it begins to leak. Once it starts leaking, it rapidly escalates from there, essentially bleeding line pressure and causing the transmission to lose it's mind. Apparently it took the right combination of daytime temperature, transmission temperature, and luck to check it under the right conditions and "catch" it failing. Once we caught it, and capped the line, the truck began driving perfectly.

I'm still at a loss as to why there was never a code thrown. Seems like when line pressure fell off and the transmission didn't get the expected results it would throw something. Perhaps someone could help me understand that better.