I've got a '79 F350 4X4 that is in need of a tranny swap. I've got a 2WD C6 out of a van that I'm gonna rebuild and swap the 2WD output shaft with the correct 4WD shaft.

I've been told there was a change in valve bodies and possibly the clutch discs between '76 and '77. As long as I get the #'s off the side of the case and get the correct rebuild kit I should be okay?

Any guru's out there know what the changes were and/or if there is a more desirable year between the '76 and '77?

Thank you.

 

Valve bodies may be different in two transmissions in the same year so the chances are the valve bodies are different but either one may work. The forward clutch plates are different and the forward drum may be different. The change happened 5/76 transmission build date.

 

According to my March 77 Transmission Diagnosis Manual (used along with a video program for mechanic training) says the following changes:

Input and Output shafts have the splines re-dimensioned. The new design can be used to service earlier transmissions.

The new design case assembly has the fluid passage bosses machined where the fluid enters. This is to provide clearence for a new low-reverse clutch piston with a slightly different shape. This case assembly also can be used to service earlier transmissions.

Special Note: None of the other new design parts described are interchangable with the prior design.

The new anti-clunk low-reverse clutch piston no longer has the ball check valve in the rear. It is now part of the valve body. The spring pockets cast into the old design have been removed.

The low-reverse clutch spring retainer now has 18 springs as an integral part of the retainer assembly.

In the low-reverse clutch pack, a wave plate has been added next to the piston. There are five each of steel, external splined plates and internal splined friction plates. The steel plates are identical to the old design. The friction plates have a new friction surface identifiable by the beige color.

The forward clutch pack belleville disc spring is thicker with more tension. A wave plate has been added plus one extra steel external spline plate. Four friction plates are used with the new beige color material. The new free play tolerance is now .021-.046 inch. The length of the inner hub has been increased. A circular groove on the outer diameter identifies the new cylinder.

The forward ring gear assembly has the length of the hub reduced and the hub is shaped differently with a radius at the base of the flange. The ring gear overall length is reduced. However the length of the external splines is increased to handle the extra plates in the forward clutch.

The valve body has been recalibrated for use with the new components. The gasket and the seperator plate are also slightly modified. Be sure to order the new valve bodies and gasket seal kits by the new parts numbers.

The new C6 design just described uses type CJ transmisison fluid instead of type F. Never install CJ fluid in a transmisson designed for type F. The transmission will not hold together.

A new installer tool IS A MUST for installing the forward clutch piston with the new lip seal. Part No. T77L-77548-A

These design changes took place with May 1st 1976 production.

 

good information---the type CJ fluid was discontinued a few years later and replaced with Dexron

 

Well...The RF #'s on the case tell me its a '77. I recognize some of the things mentioned above. I noticed the wave plates and the lack of a check ball in the low/rev piston (which I thought odd).

The valve body had some broken springs so I swapped the entire thing out with a valve body which I know works. Uh oh. I better verify the correct year of the donor valve body. If it was manufactured before that check ball was omitted, I may have a problem.

Now that I think about it, I used the output shaft of the same donor trans. Double uh oh.

After a short break from this post, I have determined that both trans cases have the exact same RF #. D7AP 7006 AA. Interesting...I did however use Type F to soak the clutches in and was planning to use it to fill the trans.