Continuing work and asking questions on my 1978 F250 with a 460 and C6 auto (happens to be a trailer special with the trans cooler lines).

So, the work progressing and one little bit at a time I'm getting it squared away. Here's the deal with the transmission: The truck does run, albeit poorly, and when I had it running it had an uninflatably flat tire. The transmission DID go in to both forward and reverse gears but the load killed the engine. So what I'm getting at is, I know it works at least a little bit. I dug a bit more into it, though. I have a suspicion that the fluid in that transmission may very well be factory original fluid. The truck seems to be incredibly low mileage despite (note: I bought it without a gauge cluster) the physical abuse it took, and the trans fluid has turned into some kind of horrible smelling varnish, which makes me think it's never ever been serviced. It really needs to be replaced before I get the engine running, I don't want to pump that stuff around the trans and potentially damage anything.

I know from the dipstick and model year that this is a Mercon fluid truck, which is convenient enough. I can still get Mercon V easily from my place of employment and as far as I understand, Mercon V is fine to use in these trucks. That being said, due to the nature of the fluid, I'm thinking I want to get as much of it out of the truck as I can. I know that people go either way on the concept of a flush though. What would you all recommend for my situation? I guess I could drop the pan and put a new filter in it, top it off, run it for a while and repeat that process over and over again until the fluid is good. But it seems to me that a full flush and refill would probably be safer in this case? I'm curious to other thoughts and opinions.

 

I recommend THIS procedure. It was written for the E4OD/4R100 but will work fine on a C6. The C6 just doesn't use as much fluid.