I have a 1978 Bronco with C6. Recently I pulled the 400 and dropped in an old 429. I put a new torque converter in. The C6 started acting up. I checked the fluid level and it was a little low (less than a quart), I added fluid and it didn't make any difference. Here is the problem. If I try to back out of the driveway in the morning right after I start it, it won't hardly engage in reverse or Drive. I have to rev the engine to get the vehicle to move. With revving, it engages, but it has a lot of slip. After it warms up, it drives fine and shifts up and down fine with no engagement problems in Drive or reverse. Then after I drive it several miles (30 or more) it starts acting up again. When I come to a stop it is like it disengages. I have to give it a little gas for it to engage, also, when I put it in reverse it takes a couple of seconds before it engages. After it engages I don't feel or notice any slipping. Any ideas? This problem is too sporatic to be the torque convertor isn't it? I double checked the torque convertor and it is the right application.

 

i'm no xmission expert. i have opened mine and am now rebuilding it. from what i see, the valve body would most likely be your problem. all the other parts are either good or way bad.
you might want to get a manual, take you valve body out, clean it real good and put it back in. i would bet that would fix it.
the friction parts, pump, seals in my transmission look inspit of the fact the fluid was black and it has 170,000 miles on it.

 

Part of the problem may be that the transmission that was behind the 400 was not valved and set up properly for a 460. Whatever the situation the transmission sounds like it has probably had it and you will need to rebuild with the proper parts for a 460 application. A GOOD transmission shop can probably do the conversion for you.

 

...I've been told....IF you dont get the troque converter nestled into the front pump body, (Push the TQ in, twist for one click, then twist some more for another click and then the TQ should slide back a bit) you wind up destroying, or at least severly damaging the front Pump.
From what you say, it sounds like your not getting enough Hydraulic pressure to do any work in the Transmission.

ALWAYS put the TQ in the transmission first, then bolt the transmission up to the engine, THEN you can slide the TQ forward and bolt it to the Flexplate.

Now you need pressure guages etc etc to do any more trouble shooting.
Dont drive it any more! You may be filling your transmission with tiny metal particals.

Hang in there with this post. There's some real hotshots on the C-6 on this Forum.

 

I appreciate the responses. I have mated quite a few engines to transmissions. I am pretty sure I did it correctly. I unhooked my transmission line from my radiator and ran some fluid out into a container to see if I could see any major particles. The fluid appears clean to the naked eye (I know that isn't saying much)The fluid is les than a month old. I changed it when I changed engines.
I was not aware that C-6's were valved differently for different applications. I assumed they all were the same internally. This 429 is no drag racer. It is a good engine, but it has not been rebuilt and it is 30 years old.
Again, when I drive this thing down the road it works fine. I drove it in the hills last weekend. I did not notice any slipping except when I was at a complete stop at idle. It is like it disengages like a manual transmission in neutural. Just a little throttle and it reingages. I am scheduled for a 1,000 mile round trip in a month with this vehicle. I hope I can figure out if this is a major problem with the transmission or something small I can resolve so I can plan accordingly.
If it wasn't for the issue of having to revv the engine with major slipping in the morning I would think that I got a bad torque convertor.
I am not wanting to drop the cash for a rebuild, but I want to figure out the problem.
I have a call into a transmission place. I will post what they have to say.