C4 Transmission Issue(wait,wait go)
 

Greetings, 1978 F-100 Ranger 302-4V with C-4 Automatic.
Story: I bought the truck about a week ago where it had been sitting for at least a year without being moved..The morning I brought it home I got about 20 feet down the driveway where i bought it and it appeared to pop out of drive, the gear selector was in drive but the transmission felt like it was in neutral, I gave it a few engine revs and it went back into drive and was fine...
Soon as I got it home I checked the fluid level idling in park and it was up to level with a nice red color..so fluid level and condition can be ruled out.

It has done it a few more times since then, but not all the time..It only seems to do it after I have moved forward 10 or 20 feet and never when the engine is warmed up to operating temperature or been driven.
More likely to happen with a cold start....few engine revs, wait... wait.. go...
Any suggestions or thoughts sure would be appreciated.
Thank you.....Johnny

It's a common C4/C6 problem. The clutch seals are old, worn, and hard. They are not sealing like they should. If you want to fix this it takes a rebuild.

Thanks Mark...For the time being can you recommend a product or additive that will help with this clutch seal problem until I can get to rebuilding the tranny?

I kinda had a feeling it was a pressure problem.

BG makes a nice trans additive to put in. Its worth a shot and less expensive than a rebuild.

Before you doctor the trans with some snake juice, is the vacuum modulator working as it should? Have you inspected the vacuum lines? Have you pulled the modulator line to see if there is any trans fluid in it? Have you ever changed the filter and filter, to include flushing the torque converter?

I would do some easy cheap trouble shooting 1st befog you get it rebuilt. Would hate to see you get it rebuilt and it just be a vacuum problem or something else easy to fix.

Here is what other FTE folks have to say. "Check the vacuum modulator and the line that goes to it. Check the line for kinks or other problems, make sure it hasn't come off.
If the line checks out, take the line off where it connects to the modulator. If trans fluid leaks out, its bad. If no fluid, it still could be bad. They're simple to replace, disconnect the vacuum line, remove one bolt that holds the clamp in place and the modulator comes out. It has an o-ring seal.

Modulators are identified by the color of the stripe. Pretty much the "go to" one is the black stripe. If they don't show that one in the catalog, go with the green stripe. Avoid the pink stripe. That one is a dual diaphragm version that has two vacuum line going to it. If by chance you have one of these, replace it with one of the other two and use the vacuum line that goes to direct manifold vacuum, cap the other line. When you pull the modulator out, be careful. There is a pin that goes in the modulator. Sometimes it comes out with the modulator, sometimes it stays in the tranny. If it comes out, don't lose it."

No, I can't. I don't know of any that work.

Thanks for your replies, very much appreciated!

I would check out that modulator. If no luck, the SeaFoam trans stuff does a pretty good job of a bandaid. Put it in the c4 of a 67' Stang and if helped the shifting issues(first to neutral,neutral,neutral, oh yes, second) for a few years now. It didn't magically fix it better than new, but . . put off that trans build for another 30ooo mi probably.

Awww Seafoam...I'll give it a shot..thanks

Lucas trans. additive is a great product and I have good luck with it several times. +1 on checking or just replacing the modulator and vac. lines. They are cheap and easy to replace. Mine was doing this for several seconds but my fluid was a little low so I added some Lucas trans. additive and it "fixed" it.

Thanks Marty...Gonna pull the modulator today so I can see the stripe color, drain a pint or so of fluid and add some Lucus in and change modulator and vacuum hose....hopefully it will resolve the issue for awhile or all together.
I will update with the results.