I have a '76 Cherokee Chief S, with the 360 motor, Quadratrac Full Time 4x4, and the HydraMatic Turbo 400. The Jeep was my grandpas, and then became mine. It was the first thing I have ever drove, and always has had a special place in my heart. My grandpa rebuilt the motor himself, and about 2000 miles later, the transmission had problems. It will only go fowards, no matter what gear you are in. Gear selector and everything is fine, linkage also. Any ideas? Might be the foward valve I was told... help!

 

If the external linkage is working correctly, you'll have to drop the pan and take a look at the internal linkage and manual valve.
You'll find a "rooster comb" with detents with a manual selector valve right behind it.
That valve is moved in and out of the valve body when you select gears by a pin on the rooster comb. If it sticks in, forward is all you get.
If you operate the shifter manually while watching the manual valve you should see how it is supposed to slide in and out of the valve body.
Possibly the manual valve is stuck, or disconnected, or the castle nut has loosened on the end of the shift rod. Take a look.

If that manual valve is moving when you operate the shifter, you have bigger problems, unfortunately. Probably time for a trans shop unless you can handle disassembly and rebuild. Fortunately the TH400 is one of the cheaper trans' to refurbish, they're relatively simple.

I googled up a pic so you can see what you are looking for.
Once it's running, see the gold color vacuum modulator on the lower right side in the pic? Change it. Check the vacuum hose too. The diaphragm in that modulator rots over time and you'll start burning trans fluid.

 

BTW, don't forget pics. Those old Chiefs are awesome.

 

 

nice