94 Will not shift, PLEASE HELP

about two months ago, i blew my main seal on my transmission. I got it repaired, and about a month ago it began to idel terribly. I found out that I had a vacuum line problem and so I fixed it. The navajo has never ran so smooth. But now i have a different problem. I have no heat and its 30 degrees outside, and it will not shift. I have every gear i can shift into myseld, and reverse is fine, it just wont do it by itself. I need my truck back desperately, ive heard maybe its my vacuum modulator for my transmission?? Please anyone with a guess help me out here, thanks

35 views and no one? Cmon guys im out of a vehicle and need to go to school!! help me out if you can

What does the temp gauge read when you say you have no heat? The biggest causes of no heat would either be a stuck open thermostat causing the engine to be continuously cooled, or from a plugged heater core. If the temp gauge reads above cold and you have no heat the heater core is suspect.. If the temp gauge reads below cold (after 10min or so of driving) the thermostat is suspect..

Check the vacuum line from the modulator for leaking fluid.

And what does a "modulator" look like? There is a tube coming from I think the rear of my transmission that has a pen-like plug in it, wtf is that? lol. Anyway, any description of the modulator or a pic of its location would be awesome, how hard is it to change if it needs replacing? thanks so much in advance

Here's a picture from Glacier991's photo gallery:

how hard is this to change? I am having the same problem

The modulator can be checked for a damaged diaphram where it connects to the vacuum tree under the hood.

It is a metal line until it reaches the intake manifold, then turns into rubber. Pull it off, if there is transmission fluid in it you need to replace it.

You can access it by either removing the converter/Y pipe (exhaust), it is under a heat shield on the passenger side of the transmission. Or by pulling back the carpet and removing the panel that is covering the hole in the floor where the shifter would come into the cab if you had a manual transmission. It is a PITA but if you need to replace it, that's how to do it.

Welcome to this forum! It's not exactly easy since it has limited space to work in, but it's doable.

Searching on "modulator" should yield good info.. Check out thread like
Fixing an old 1st Gen (start at post #23).

After ready the threads on replacing the modulator I decided I didn't want to start removing 15yr old CATS to do the job from underneath. Instead I went through the transmission access panel pictured below.

You absolutely do not have to remove anything to access the modulator, with a mirror and some ambition you can just reach up from underneath the truck. A ratchet and socket and a ratcheting wrench is a lifesaver. All you need to do is get under the truck, legs toward the passenger side. Place the mirror (sisters compact worked well) up and angle it for vision. I had a fashlight that i lit up the mirror with and voila, I could see everything perfectly. It was very very easy, sorry if the explaination makes it sound hard. Once you know what you are working with, it is a breeze. To reach it, I places my right arm up through a space a little toward the right, and it fits perfectly. It is easy and you dont have to remove anything. Let me know if you cant figure it out from my description.

It is definitely doable from underneath but really is not a fun job in a very cramped space. The picture BB posted was designed to show you how it is held in place...you undo the nut that holds the heat shield, then you remove the bolt/stud that holds the retainer on the moduator... but 94Jo is right... leave the seats in and do it underneath, or buy one and have a trans shop do it. They will charge you an hour's labor tops.

(I pride myself on doing all my own work whenever possible, and last spring I was pressed for time and decided to pay to have this job done - and was glad I did. It was worth it NOT to have to do it myself - and I NEVER say that!)

I have a 94 explorer 4x4 and I bought a new modulator the one I bought looks the the one in the picture but the one I took off doesn't have that screw thing on the back . It just has a hole with a cap on it. Will it still work?

The one in the picture is adjustable. Your original one doesn't have the adjusting wheel. Some have a recessed adjusting screw.

The new one didn't come with the wheel on it

it will be fine. Like Brooklyn said, there are two main types, non-adjustable (stock) and aftermarket "adjustable" ones. Of the adjustable variety there is the one shown in the picture, and one that has a screw in the end instead of the thumbwheel (the one that has the screw in the end is not reachable to aqdjust once installed and pretty useless if you ask me.) Any will work. Install what ya got.