Automatic transmission not shifting in 1986 Ford

[crw]

Codes? This is a 1986 cabuerated 351W Ford. The only thing electric on it are the headlights. ;-). And thats the best part of it.

After removing the pan, the fluid looked a lot better than I expected. No problems that I could detect inside. Refilled with new Dex III, but no improvement. I may take it to someone and see if they can diagnose.

 

[Cujet]

As suggested above, the vacuum modulator may not be functioning properly, that will cause this exact symptom.

My first guess would be that it's getting no vacuum.

So, carefully check your vacuum lines. There should be a line from the intake manifold to the vacuum modulator on the side of the trans. It could be clogged, failed, leaking, or it could be attached wrongly, and to a device that is not allowing vacuum.

You could try to hook a line to the vac-mod, and run it in the drivers window. Then pull a really strong vacuum on it while driving (you can guess how I'd do this)

Follow the line up from the trans and inspect really carefully. Try hooking it directly to intake manifold vacuum in another location. Eliminating any devices in the circuit. (sometimes there are vacuum thermostats and other stuff in the vac-mod circuit)

 

[crw]

Thanks, I'll try that next. When I was dealing with the pan I didn't see anything that seemed to fit the description, unless the vacuum modulator could be on the front, on the engine side of the trans..?

 

[artificialist]

Originally Posted By: crw
Codes? This is a 1986 cabuerated 351W Ford. The only thing electric on it are the headlights. ;-). And thats the best part of it.

After removing the pan, the fluid looked a lot better than I expected. No problems that I could detect inside. Refilled with new Dex III, but no improvement. I may take it to someone and see if they can diagnose.

In 1986, Ford engines had at least some kind of electronic control even if they were carb engines. Unless you made modifications, you have an O2 sensor and feedback carb.

 

[crw]

I hate it when threads end with no resolution. I finally got around to replacing the vacuum modulator. When the old one came off, I could blow air straight through it, and I thought, "This must be the problem!" I went and bought a new one, installed it (with the rod, I'm assumin'), but, no dice.

Truck runs in first gear while in "D". Shifting it down to "2" gives second gear, and it drives great in those two gears, but freeway trips are out of the question.

My kids have named the truck "Ed". The phrase "Ed is dead" has been repeated around my house a lot lately...

 

[OVERKILL]

Is the kickdown lever functioning properly?

 

[OVERKILL]

There's a thread on the Ford Truck forum with basically the same issue you are having:

http://www.ford-trucks.com/forums/1011720-c6-wont-shift.html

They have some troubleshooting stuff listed.

 

[crw]

Whoa! Chasing that vacuum line up to the engine bay... It is not connected, and hasn't been for some time.

 

[OVERKILL]

Originally Posted By: crw
Whoa! Chasing that vacuum line up to the engine bay... It is not connected, and hasn't been for some time.


LMAO!!! Well then connect it! LOL! That means you've also had a massive vacuum leak for a while too!

 

[crw]

Well, there is no open connection that I can find. So the engine is probably ok, and not under a leak. I'm guessing the previous owner gave up trying to connect it. I need to buy some extra hosing and route the vacuum to the mini plastic "manifold", and from there I will then have enough connections. There are other hoses that look close to death from dry rot, so I have some work to do. As you can tell, I find about 5 minutes a day to sort this out...

 

[itguy08]

Originally Posted By: artificialist
Originally Posted By: crw
Codes? This is a 1986 cabuerated 351W Ford. The only thing electric on it are the headlights. ;-). And thats the best part of it.

After removing the pan, the fluid looked a lot better than I expected. No problems that I could detect inside. Refilled with new Dex III, but no improvement. I may take it to someone and see if they can diagnose.

In 1986, Ford engines had at least some kind of electronic control even if they were carb engines. Unless you made modifications, you have an O2 sensor and feedback carb.


Yeah - probably EEC-IV. Relatively simple for the cerebrated engines but it may use the infamous TFI module....

 

[crw]

Yes, there is a light that says "Emissions". It is not lit. In my Mini it is, perpetually.

 

[Lubener]

Make sure the kickdown linkage at the throttle body has not fallen off or bound up. Also pull the line off the vacuum modulator, if fluid drips out, it is bad. If those does not work, an overhaul is likely. If the band is out of adjustment, it soon will need to be replaced anyhow. The lining is so thin, it likely is worn out.If it is a C4 or C6, it originally used Dexron. IF it is a C5 ( C4 with lockup) it used type H. Type F was phased out long before 1986.

 

[crw]

I rerouted the vacuum lines in the engine bay, (a rats nest) and the tranny is working! Thank you all for holding my hand through this.

 

[OVERKILL]

Excellent!!!

 

[crw]

I can surmise now what happened. Previous owner had a failed vacuum modulator. (It had a hole.) it was probably drawing tranny fluid into the engine. Rather than replace the vac modulator, he simply disconnected the vac to it and rerouted things so that it would isolated... And the C6 continued to run.

 

[Lubener]

Sounds like something a shmuck would do.