Allison transmission tech?

I don't know if anyone is familiar with Allison transmission's, they are all different but when they have a problem, it's probably a similar cause.

I have a WTEC3 Allison B500 mated to a Series 60 engine in a 2003 MCI. I bought the vehicle from auction, it was supposedly having transmission issues. I drove it for three hours, no problems. Then, the third hour when I'm 30 minutes from my destination, it started shifting harsh. When I came to a stop, it wouldn't move without shutting the unit off, and restarting it, because it would not go into neutral.

I checked it for codes and it was throwing a speed sensor code. I replaced the speed sensor, and to no avail, it did nothing.

Basically:

1. When I start it up, there are no codes.
2. When I put it in drive, there is a 2-3 second delay and it clunks in, it is not smoothly engaging.
3. I am not getting full power to the transmission when I step on the gas.
4. When it tries to go from 1-2 or 1 to lock up, it lights up "1" gear on the display, and then gets locked in 1st, but the transmission is internally stuck in neutral.
5. I shut the unit off, restart it, and it does the same thing. This is even after changing the speed sensor.
6. Before and after changing the speed sensor, it's doing the same thing.

I'm trying to distinguish if there is internal damage in the transmission, or if it is an electrical issue. I was hoping someone has run into this before on a related Allison transmission, and they can just be like, "It's probably this or that," or "Oh, that's a classic transmission failure."

This thing drove fine for three hours then just acted up. Hot or cold, it doesn't matter, it still does the same thing. Any help would be appreciated, thank you.

 

Thanks for the reply. I do have the laptop with Allison software. I’m not sure what I’m looking for to diagnose the problem. I have identical units that I could use for reference.

I bought it from auction, it said it was having transmission issues. I drove it away and it worked flawlessly. Then, it just started acting up and has not recovered.

It is not exiting or shifting first gear, and moves sluggishly. It is not receiving full power, or not allowing full power. Once it hits the threshold to exit 1st or go into lock up, it defaults the key pad to 1, and internally the transmission is in neautral and will not go anywhere, or allow me to press the N button to return to neutral. I have to power it off to clear it.

thanks!