Here are the truck specs: 1992 F150 E4OD, 4.9L 300, 4WD with manual BW1356 transfer case. Truck has 84,000 miles.

My truck will only shift into reverse gear and has no forward gears or park. The only way I can keep it stationary is by engaging the parking brake because it will start rolling when it's just in park. I've read through a few threads and it appears that if this was a 2WD, it would indicate something had broken inside of the transmission, likely the forward clutch. However, because this is a 4WD, it may have something to do with the transfer case or the differential. In 2H, I can only get reverse, and cycling through 4H and 4L still only get me the reverse gear. In 2H when I shift to manual 1, I can hear a clunking sound from behind the cab and there's a slight change in RPMs, but the truck has no go. There are small changes in RPM when I put the shifter into manual 2 or drive, but no forward gears are engaging and I don't hear any sound from the transmission indicating the truck is trying to go into gear.

When I drove it about three days ago, the truck was fine. No odd noises and no shifting problems. I had a leak in my valve cover so the truck was out of commission for two days while I waited for the new gasket and took off the exhaust manifold, EGR and throttle body to access the valve cover. I don't think anything I did for that job could have caused the transmission, transfer case, or differential to have gone bust.

If this is indeed a problem with the transfer case or differential, how should I go about diagnosing the issue and then curing it?

 

Sounds like the end of the line for that trans.

 

When your transfer case is in 2H... That is the same as a 2 WD truck.
When you start to pull the transmission for a rebuild, that is the time to check your transfer case.

 

A transfer case works or it does not work. It can't work in reverse but not in forward.

 

When you replace or rebuild the trans make sure you flush the cooler and lines out real good. The fluid left in there is contaminated and you don't want that pumped right into your new trans.

 

Start it, put it in drive, it's not moving I understand, then put it in park. Do you hear a ratcheting sound? If so the output shaft is turning and you probably have an issue in the transfer case. Normally if the range hub/fork is bad, you can get movement by putting it in 4WD low, but not always.

 

I got the trans out yesterday and took it apart today. The frictions and steels in the forward drum were pretty badly burned, and the drum itself had some evidence of heat damage. I'll be replacing that along with overhauling the whole thing as time allows. Thanks for your advice, everyone.

 

I do not see any damage enough for it to cause no engagement. Slipping maybe but loss of drive, no.

Keep looking and check everything, especially the one way clutches. Any good rebuild will get those parts too. Do not forget to air check the clutches before you get too far.

 

I’ll check that. I’m using the FSM’s diagnostic guide to eliminate all the potential problems. The forward drum was the only hard part that showed any damage, the front/reverse Sun, the forward planet, and the output shaft all appeared okay. Fluid level was fine, the shift linkage I made sure was tight, and I also checked the valve bolts were torqued to spec before dropping the trans. The only thing I didn’t check was line pressure.

The truck was stalling out in reverse gear when it got hot and would slip from 1-2 occasionally so the trans was already due for some TLC. When the rebuild kit arrives in the mail I’ll go through all the components and hopefully find the smoking gun.