I am pretty sure my c6 transmission failed today wile I was on my way to an event. I was cruising at 60mph slight bang then it sounded like the tailshaft fell out did not get any vibration it did snuff my engine out by the time I got it pulled up on the side of the highway. Got the car towed home did not have much battery left once I got home engine seems to turn over fine nothing sounds bad I will start the car tomorrow and check every thing is ok there but I think everything is fine with the engine car rolled and moved fine loading and unloading it no fluids leaking from any parts oils all look good and clean and smell normal.
once I work out what failed if it is the gear box I was going to pull it apart not sure if there are places I should look first inside the trans. The trans has done no work since rebuild and worked great the place that built it for me is no longer around after 30years of building transmissions sadly when I got a donner box I got an early one 1966. I will upgrade to a later model case this time.
Has anyone had a failure like that?
I’m just verifying, you’re saying this is a 1966 model year C6?
The early model year ‘66-‘69 C6’s just used a splash oiled one-way clutch (sprag) in the rear of the case. Sometime later in the ‘69 model year Ford changed to a pressure oiled one-way clutch, and all later C6’s were pressure oiled. Just a wild guess at this point, but with what you describe it’s possible your one-way clutch failed & locked up. I’ve personally had it happen once, on my ‘66 7 Litre Galaxie, and have heard of other failures. It can especially happen on these older vehicles that don’t necessarily get driven a lot. Years ago Ford had a replacement one-way clutch rear race with the required lube hole and instructions on where to drill a small hole in the rear of the case to intersect the existing fluid return passage. Early ‘66-‘69 C6 cases can easily be modified to have the pressure feature, and all replacement one-way clutch rear races come with the lube hole passage now days. I’m sure this discussion has come up here before and I’ve posted the instructions, but I can do it again for anyone it might help.
I would check under your vehicle first before you start it, just to visually check for anything that is obviously wrong, like a broken case or tail shaft housing, or anything else that might have caused your issue. Most of the time that’s not an issue, but always good to make a thorough check first.
edited to add instructions

