C4 won't shift into 3rd gear when cold

Originally Posted by forthman

I am not sure. But the kickdown thing, is the vacum signal/mech. operation i thought.
"this is why i went manual"
The kickdown lever i think changes the valve body fluid routing. Sorta over rides the shift selector.
I am thinking the modulator,govenor,shift down lever all wor together.

Then might be when you get the Org. problem figured out the down shift thing might go away.

I was wondering if low fluid pressure could be part of the problem?
Ever checked to see what you are getting for pump pressure?

Ha! that is why I wish I went manual now. Anyway, I have not check the pump pressure, that would require a trip to the tranny shop. Which is probably what I should have done in the first place. Is the governor the servo or is it separate part? I replaced the valve body and modulator with no improvement so when the servo gets here hopefully that will work.

Reason i was thinking pressure.. Was it goes into reverse cold.
Reverse has a higher apply pressure. (atleast as i remeber)

or would a sticking direct pressure plate? Be possible?
I better quit guessing.
lol... I need Paul to chime in

Well, the new TCI servo kit came today. The bad news is, after looking at how long the servo shaft is, and how close the servo sits to the floor tunnel on a fox mustang, it appears that I may have to remove the transmission cross member and collectors and lower the back end of the trans to gain access to the servo. The back of the engine is only a few inches from the firewall, I hope there is room for the engine to tilt backwards enough to lower the tranny. Has anyone ever done this before? It could get ugly

I have only replaced a servo with the trannt out of the car.

There is a small square thing that hooks to the band and seats in the servo shaft slot.
It could be a crap shoot trying to get it installed under the car.

So you replaced the modulator BUT did you adjust it any .They need adjusting .I set mine on scales to a certain weight in LBS . The more weight on the modulator the more sensitive they are so may help the part throttle downshift ..

Originally Posted by gregaust

So you replaced the modulator BUT did you adjust it any .They need adjusting .I set mine on scales to a certain weight in LBS . The more weight on the modulator the more sensitive they are so may help the part throttle downshift ..

The new modulator is adjusted clockwise (in) 1 turn more than the one I took out. I did this to raise the shift point. Maybe I'll adjust it back out to where the old modulator was and see what that does.

I loosened the kickdown linkage and it seems to have helped some, it will drop into second sometimes instead of going right to first, but it still is downshifting erratically and surges from third to second.

The new problem with it feeling like I'm riding the brakes when I'm in third is also still there (I thought it went away after adjusting the bands). It's hard to describe, but when you press the gas down in third gear it feels like there is a drag, the converter gets squishy, the rpm goes up like 500 rpm before the car begins to accelerate, as if you were riding the brakes. The trans also seems to be running hot and the fluid smells a little cooked, though it's bright red and not burnt. Unless someone has a better idea, I think I'm going to remove this new TCI valve body and put the old one back in. The TCI valve body and modulator has created a whole new set of more serious problems. I can't figure out what is causing the problem, and no one is coming up with a good reason so maybe I should just take it out. At this point, I can live with the problem of no third gear when cold, at least it worked okay when warm.

This is turning into a nightmare...

I just got an idea; is it possible that I have the wrong valve body? My C4 is a (square) pan fill with screw in modulator, in a 1979 Mustang. A transplant? The TCI valve body I purchased was for all C4 1970 and newer. Is it possible the VB is not corect for my trans? Could that be causing the new problem with binding in third gear and erratic shifting?

As you can see, the two valve bodies ARE different.

Original (left) Part # RF-D0AP-7A101-AU
TCI (right) Part # RF-D7ZP-7A101-AA

I'm really upset at TCI for not covering this in their directions. And I'm really mad at myself for not comparing the two before installing it. There is some metal shavings in the pan now and the fluid is cooked. This may have done catastrophic damage to my transmission? I'm waiting for it to finish draining so I can put it back together with the original valve body and see if the thing works anymore. The servo I got from TCI is also for a 70 and up c4 so I don't know if I should use that servo either. I sent TCI a support ticket about 4 days ago and never got an answer. Help, Paul, what's the poop?

Casting #'s DO = 70
D7 = 77

Now i am thinking all valve bodies 70 and up are them same. (function)
Tho they might look a bit different the function the same.
The earlier ones had a different shift pattern.

The burnt smell is not good. Clutches are burning.
Your new TCI valve body i bet make more pressure.
In 3rd you said it felt like the brakes were on.
The burnt fluid suggests you were in 2nd and 3rd at the same time.

All i can think of is the band not releasing or dragging bad.
This would put a bunch of stress on the direct clutch pack and the band.
Making a ton of heat fast.

I think i am back to Paul's first post. The seals are old/worn/hard on the direct clutch pack.
With a possible servo stick too boot.
Might be time for a rebuild. Get all new seals and gaskets. Plus add some clutches.

I am still amazed at the one i have rebuilt. I flat out abuse it and it shifts so hard my teeth hurt.
Got all my info on how to modifiy it from this board.

Well, I put the original valve body back in and adjusted the modulator and it seems to be working okay now. It still won't go into third for about 5 minutes, but warmed up its back to shifting hard and barking tires in second and third gears. And the kickdown is working good now too. So that TCI valve body was causing the 2-3 bind. The odd thing about your theory of the TCI having higher pressure is it didn't manual shift as hard or fast as my old valve body. It was downright wimpy! I think someone may have done some tuner mods on my original valve body. If you look at the pictures closely, the two are more than just a little different. My valve body has the spring under the filter, the TCI has it in a different location with a pin retainer. There are also several differences in the location of the valves and passage ways and some holes drilled in the valve bodies are in different locations. Or perhaps the TCI valve body is just a defective unit. Anyway. All I wanted was to fix the cold shifting issue and get me through the summer, because the motor and transmission will get redone over the winter. It's back to shifting good when warm and I will just live with the cold shifting problem. I just hope the binding / over heating didn't do any major damage to the clutches or bearings.

Thanks for all the help....

I'm gonna leave well enough alone