Folks,

I recently did a C6 rebuild on my 78 4X4. After the rebuild, when I go for a drive, the transmission does not AUTOMATICALLY shift out of 1st.

1. I can shift MANUALLY from 1st to 2nd with no problem, but it never goes into 3rd in D. If it was a system pressure issue, I suspect that I couldn't engage at all?
2. In Drive it just seems to be in 1st the whole time no matter how high the rpm.
3. I checked the vacuum at the modulator and I get 18 in .
4. I have tried every color modulator band and have the black one in now.
5. During the rebuild, I cleaned the governor, so I don't think it would be jammed up since it wouldn't shift even when I first drove it.
6. During the rebuild, I cleaned the valve body.
7. I confirmed the kick down is free.

Here is the last couple of things I can do, but I don't know if it can help.
1. Could the intermediate band be the issue if I can shift in manual?
2. The mechanic said it could still be a governor gunked up, but I'm skeptical since it never worked after the cleaning.
3. The filter screen pan from the rebuild seems to sit higher than the original that has a pipe that hangs lower. Is this the suction or the return from the system. If it's the suction I can put the original in.

Is it bad to drive her in manual if I need to? Obviously I'll keep the speed low since I can't get into 3rd.

Can anyone of you wise soles out there help? When I air pressure tested the transmission before the install, everything engaged like it was supposed to and all of my clearances were solid.

*sorry for the long post, but I'm out of ideas*

 

I am no automatic expert. I briefly drove one with a diesel swap. I had the same issue when I first started using the truck. It ended up being a vacuum leak. I would really review your vacuum lines and hookups. Once I got that figured out it worked fine. I never even connected a kick down.

Secondly, are you SURE you have enough tranny fluid in the thing? The torque converter and transmission takes a lot more than just the amount that goes into the transmission. Probably 5-6 quarts at least. Being low on fluid will cause it not to shift as well.

I don't see how you could possibly damage it by manually shifting. I think if something was wrong to the point you could mess that transmission up you would hear it or feel it.

 

I checked the vacuum in park and I got 18 inches at both the carb and at the modulator. From what I've read, that seems to be the spec.

My tranny fluid should be fine, as I've checked it while running. It comes up in the right target. If I'm pulling through the filter screen as my suction, I can see where the new pan with the higher spout could be the cause. Other than that, I'm out of ideas.

 

Is it possible that it's the governor if I hear some slight chirping noise coming from the transmission when I first start it and it's still in Park?

 

Welcome to the forum. Is the pin still in the vac. modulator? It's easy for it to fall out and not be noticed. Also there is a transmission forum on the site. Tranny pros hang out there. Put the original filter screen back in.... there are two, one for cars and one for trucks. The truck one hangs lower. Good luck with it and let us know what you find out.

 

Sounds good, bud. I saw that there was a better forum, but I didn't want to be a jerk and post in both. I'll do it.

Also, do you think the filter screen has anything to do with it? I always assumed that that was the return. I guess air can be mixing in if its not submerged when it returns.

 

Sounds to me like the line going to the modulator is collapsing under increased vacuum. Happened to me once--liked to drove me crazy til I figured it out. If it works, that'll be $59.95.

 

Ford shop manual says; vacuum leak in line to diaphragm unit, Linkage adjustment'
Fluid level, Clutch or band application, oil pressure control system, Governor, Dirty or sticking valve body.

 

Guys, sorry for not responding earlier. I've moved the conversation to a more appropriate location in the transmission forum. I found that my governor weight (small steel cylinder) in one of the valves was missing. I'm still not sure of this is the final solution, but I'm looking into it.

For those interested, here is the link.

C6 Wont Shift Automatically - Ford Truck Enthusiasts Forums