So this past weekend I finally got my f250 out on the road. It ran great other than having dry rotted tire noise it was pretty good. When I was driving the truck I noticed that I couldn't feel the transmission shifts or tell that it was shifting unless I would change it manually. I've never had an automatic transmission before my other 86 f150 is a manual and even my daily driver corolla is manual as well.

Could anyone teach me how this transmission operates. I have done some research on the vacuum modulator and kickdown rod maybe those things have something to do with it. This is pretty new to me as funny as that sounds.

 

The C6 can easily shift quite smoothly - enough that you might not notice it if you aren't watching. But, you should be able to detect it.

But, if your truck hasn't been on the road for a while then the governor may be gummed up and it may well not be shifting. I had one that did that after not being driven for quite some time - it didn't shift if I didn't force it to do so with the shift lever. But when I put a pint of Sea Foam transmission tuneup in it the thing started shifting much better almost immediately, and within 500 miles it shifted fine every time. However, I had changed all of the transmission fluid, so you may need to do that as well.

Another trick I've read, although I've not done it, is to drive as rapidly backward as you dare. Supposedly that directs transmission fluid in a way that may clean the governor.

 

I disassembled and rebuilt my C6 transmission. This is what I observed about how the transmission functions. There are some fine details that I might not have down quite right, but the majority is there.

The engine turns the flex plate/flywheel which is connected to the torque converter. The torque converter has 2 different functions. The first is to turn the hydraulic pump (#500) in the transmission which creates hydraulic pressure with the transmission fluid. The second is to transfer rotational force to the first clutch pack. You can see the input shaft (#670) has splines on the left (for the torque converter), splines in the middle (for the pump gear #530) and at the end which connects to the middle of the forward drum (#554).

As for the pump, this fluid goes through a series of valves and springs in the valve body (740) which control when pressure goes to the clutch pack pistons (965, 964, and 966) to compress the clutches (126, 110) and plates (106,108,130) together. When the clutch packs are compressed together, they stop slipping which allows the input shaft rotation to go to the other side of the clutch pack. This turns a device called a planetary (582 and 584) which is connected to the output shaft (678). The output shaft is connected directly to the driveshaft (via transfer case if you have 4x4) which goes out to the vehicle wheels.


Complete assembly diagram




The piston (964) compresses the clutches/steels (108/126) which lock the outside of the drum (554; normally free-spinning) to the ring gear (592) which spins the planetary (582) which is connected to the output shaft (678).



Near the end of the output shaft is the governor (680) which spins with the output shaft. This centrifugal force propels the weighted/spring-loaded valves outward at certain speeds. This helps control when the vehicle shifts up and down. The vacuum modulator (160) tells the transmission when to shift up and down (based on engine speed/vacuum pressure) by opening/closing a valve (163) too.


Governor

 

The governor controls up shifts as well and down shifts. It and the modulator work together. The governor is controlled by road speed, the modulator is controlled by demand on the engine.

The valve body and all those springs work on pressure. That is how it shifts "automatically". The governor and the modulator vary this pressure.

 

Updated. Thanks. Can't really tell all the functionality just from taking it apart.

 

Awesome post Braggs I opened the thread several times intending to organize a response and mentally forming one but never could. Nice job and Franklin 2

 

Thanks fellas. I appreciate the responses. I hope this could help me in the future.