The wife's 73' was running and driving well, then it began hesitating going into drive. I drained the fluid, changed the filter and replaced the ATF and its doing the same thing. Any ideas what else I can do?

 

So it takes a while to engage into drive? Sounds like the clutch band is worn.

 

Yeah, it was fine one day and the next it takes like 5-10 seconds to engage after put into gear.

 

Does it make a difference if the trans is cold or up to temp? I am not an auto trans expert by any means.

 

Doesn't seem to. My brother inlaw says he thinks it's in the valve body, but I wouldn't let him change the tire on a bicycle.

We were going to take it to NPD a couple weeks ago and it stopped idling when we would decelerate, so we brought it home. Cleaned the carb and put a new fuel filter on it and now it's hesitating going into gear. Changed the filter and the fluid, but it is doing the same thing.

 

Have you checked the vacume tube going to the trans modulator for a leak/dry rotted? Or you might ck if you have fluid in the tube going to it. That is a bad sign.

"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."

 

I but I will right now, thanks!

 

So I swapped in the modulator from the 77' and no real change. Still jumps right into reverse, but hesitates going into drive or any forward gears. Will swap out the vacuum lines going to the modulator tomorrow.

 

Have you tried adjusting the band? I think it's more likely a sticky valve or pump problem but the band is easy to adjust and only takes a little while to do. There's lots of threads on how to do it. Good luck and I hope you find an easy fix.

 

My first suspicion on a C6 would be the forward clutch.
The very common problem that they have doesn't quite fit your symptoms.
When the seal in the forward clutch goes usually it's a gradual thing. It starts as a delay in going into forward gears when cold but reverse is fine. When it warms up, it's fine. The delay gets longer and has to warm up more until finally, the trans no longer goes into forward. Reverse is still okay.
It has to do with the forward clutch apply piston seal. It gets hard with age and doesn't seal when cold, but once it warms up it will seal enough to get the piston to apply.
The sucky part is, to replace the seal, you need to tear down the transmission.

NOTE: If you want to adjust the band (on a C6 there's only one). The adjustment is on the driver's side of the tranny, at about the 11 o'clock position to the manual shift selector.
There's a nut and stud, loosen the nut, tighten the stud to 10 ft/lbs. Now, back off the stud exactly 1 1/2 turns. Hold the stud to keep it from turning and tighten the lock nut.

 

Ive rebuilt many C6 trannys in my life and I can say with a degree of certainty that it is your servo piston as stated by Mikeo0o0o0. Very easy to change out just make sure to look at the code on the cover before purchasing a new one, I recommend getting an "R" code piston. Remove bolts, remove the piston, gasket and cover, prepare for ATF squirt, separate piston from cover and spring, put in new piston and install.

 

This thread might just resolve my problems too..LOL...sweet!

 

Can this be done w/ Trans installed?

 

For anyone who would like an update on this... It just stopped dong it. Did nothing, changed nothing... Drove it for a week and it just fixed itself.

 

The servo that F250_Super_4X4 was referring to is located on the passenger side of the transmission and can be serviced/replaced in the truck.
I was actually referring to the forward clutch apply piston. That's located internally and to service/replace the seal you need to completely tear down the transmission, so it needs to be removed.