Extended amount of time before 727 flows fluid and shift/pulls.

[1970gator]

I recently bought a '70 charger that is a numbers matching 383/auto car.  The cars mechanicals were rebuilt in the mid-90s during a freshening up of the car.  The car was driven very little since.  In fact, when I bought the car a month ago it hadn't even been started in about 5 years and was sitting in a huge puddle of transmission fluid (as you might assume, lol).  Anyhow, I've done all the basic maintenance on the car it would need.  I also installed a cast aluminum trans pan with drain plug (to eliminate future trans gasket leaks) and changed the filter and topped off the fluids.  I've owned tons of 727s and have even rebuilt a dozen or so never having an issue.  However, I usually install a trans kit to allow fluid flow in park and I have not done that to this particular trans.  My issue is that it takes an extended amount of time in neutral flowing fluid (a good solid minute) before the trans wants to pull.  This happens even after as little as an hour of sitting parked.  However, once the fluid is circulated the transmission pulls strong and shifts properly.  Any thoughts?  Just FYI, I assume it is the original torque converter but I can not confirm that.  I can tell you the engine has a higher lift/longer duration camshaft than stock.  Fluid levels are correct and not over/under full.  I suppose the pump in the transmission could be weak, but I've never actually ran into that issue and with the car being an original 70,000 mile car....I kinda doubt it is a pump issue.  I tend to think maybe sticking valves or bearings in the valvebody from sitting?  I've only put maybe 10 miles on the car.  I'm hoping if it's a valvebody issue that driving might help correct the issue.  Any thoughts or ideas would be greatly appreciated.

[John_Kunkel]

After idling in Neutral is the transmission reluctant to pull in both forward and reverse? Could be a simple case of hardened/shrunk seals that don't hold pressure anymore.

A '70 383HP should have the 11" converter, you can verify by removing the dust cover at the front of the converter housing.

[1970gator]

After idling in Neutral is the transmission reluctant to pull in both forward and reverse? Could be a simple case of hardened/shrunk seals that don't hold pressure anymore.

A '70 383HP should have the 11" converter, you can verify by removing the dust cover at the front of the converter housing.

After idling in neutral for a good solid minute it will shift into forward and reverse with a good solid shift like as is normal.  However, prior to that if you shift into either forward or reverse it labors to pull forward or back up.  It improves with every shift through the gears until after about a minute when it has begun to behave normally.

[375instroke]

Big puddle and shifting fine after being in neutral leads me to believe the torque converter is draining back into the pan.  Does the fluid level go up a lot after sitting?  My car, 50 years old and 130,000 miles, does this, but takes about five to ten seconds to go into gear normally after sitting for a day.  A full minute, though, and how to fix it?  Is there a check valve in the valve body, or is it in the pump, or somewhere not easily accessible?

[John_Kunkel]

Converter drain back is perfectly normal and shouldn't be an issue after idling in Neutral for a minute or more.

Try some additive like Trans-X or Lucas, if shrunken seals are the problem it might help.