I think my F250 has the C6 3 speed automatic (The spec's for the HD F250 say that was the trans in the base model XL that I have).

But NO amount of coaxing will cause the trans to kick down.

I don't see a vacuum modulator on the trans, is it an electrical control? If so, where is the control located, is there a way to test it, and what triggers it to kick-down? (a sensor somewhere?)

The more I learn about this F250 the more I seem to need to learn.

After a lot of thought about selling it once it's all repaired, I decided I just like it too much to let it go. Now I need to fix everything so it works. (Some day I may even patch the massive amounts of rust on the body, but for now I need a 100% functional truck.)

As much as these old fords ask of us for maintenance, how come they are so loveable? They must have kitten DNA...

 

The c6's are non-Overdrive trannies....THATS why you can't get it to kickdown....

 

That makes no sense
Even a 3 speed should downshift if it needs to
Just like my E4OD will drop from 3rd to 2nd on a steep hill

 

My bad.....You're right....

Revision-

The TV cable/bushing wear out, or stretch and can cause issues....

There....

 

If you have a C6 then there is a vacuum modulator, although it controls the shift points and not the kick down.
The kickdown is controlled by a rod connected to the throttle linkage and connected down to a lever at the trans. The lever is on the same spindle as the lever that the shifter linkage is connected to.
The C6 has 17 bolts around the oil pan if you want to check it.

 

On a C6 the vacuum modulator were screw in and others were held in with a clamp into the back of the transmission just above the pan.

Screw in Vacuum Modulator:


Clamp in Vacuum Modulator:


The linkage:


Screw in:


Clamp in:

/

 

If the door jamb sticker is still on the truck look for the Transmission Code. If it is a "G" it is a C6. If the code is a "T" it is an AOD (highly unlikely). If it is an "E" you have an E4OD which is an electronic controlled 4 speed overdrive transmission.

Here is an example of what I am referring to:


Once you determine which transmission you have, we can help diagnose the issue accordingly. Another telltale sign if you have an E4OD is the Overdrive on/off button on the end of the shift lever.

 

Oddly enough I have a Trans code "K" which you haven't covered.

Do you have a link where I can look that up?

 

"K" = C6 Transmission.

 

OK that answers that question. Thanks

I will have to dig around under the hood a bit. Many of the vac lines in this truck are rotted out so I will check any heading south from the engine.

I don't remember seeing the kick down linkage at all when we were replacing the exhaust manifolds. We did jack up the engine off of the mounts to replace the oil pan gasket last fall, we could have bent the rod if it's there (although prior to that is wasn't kicking down either).

So the vacuum modulator on a C6 just tells it when to shift up? Hmmm... I will have to go lay under the the thing and take a dirt's eye view of the situation.

 

Is this the kick down linkage? Can't seem to find where it hooks up in the engine compartment.



The modulator seems to have a newer line on it replacing the original metal line. VERY rusty



I can't find the origin point for the vac for the modulator - must be behind the engine near the firewall.

 

That doesn`t look like a C6. Can you get under and count the number of bolts that hold the oil pan on?

 

C6 would be the only one in a truck that year with the vacuum modulator on it.
The vacuum modulator does the same job as the TV on a AOD. The vacuum modulator controls the oil pressure.
Yes that cable is the kick down linkage, It does go to the engine compartment. I think it is hooked to the throttle shaft.

 

Awesome, subford! Thank you. I'll go back out and look. The linkage does move freely so it is either disconnected or not adjusted.

 

This is for a 1992, I hope the 88 is the same.

Kickdown Cable, Vehicles with C6 Automatic Transmission

Removal

1. Remove throttle body splash shield if equipped.
2. Snap kickdown cable off throttle body ball. Using pliers, depress lock on kickdown cable conduit and remove it from bracket.
3. Raise vehicle enough to gain access to transmission and still be able to access throttle body area.
4. Snap kickdown cable off of transmission kickdown lever.
5. Squeeze tabs on kickdown cable conduit and remove cable from bracket and from vehicle.

Installation

1. Make sure that throw-away red spacer is secured on cable end fitting at throttle body end. If red spacer is not present, reuse a discarded one.
NOTE:
Spacer provides 5mm or 0.2 inch gap between metal cable end stop and plastic end fitting.
2. Insert conduit fitting into engine bracket and slide cable end fitting onto ball stud on throttle lever.
3. Route cable down to transmission and insert conduit fitting into bracket and snap into place.
4. Snap cable end onto ball stud on transmission kickdown lever.
5. Ratchet cable adjusting ratcheting mechanism to correct setting by rotating to wide open throttle (W.O.T.) position by hand.
6. Remove red spacer.
7. Install throttle body splash shield.