My earlier reply was directed at the statement that the cooler lines, if rubber, could be sucked closed.
They can’t because they always see pressure.

You are correct, the lines normally see 15-30 psi but varies.

It would be interesting to see how much flow makes it to the trans for guys that mount their cooler at the back of the car.

while maybe the word sucked is not the best choice - lines fail - if you have worked around hydraulic systems long enough you will see a soft line failure - like a brake hose that fails and blocks flow but does not burst - what happens is the hose breaks down and the oil gets between the layers and literally can collapse the line closed - like a valve

"It would be interesting to see how much flow makes it to the trans for guys that mount their cooler at the back of the car. "



could you explain, please ? i don't quite understand, as i'm kind of a dunce at times.
thanks !

Hydraulic system “friction”. Think of electric circuits, the measurement for resistance.

i get it now.
thank you for the explanation !

I'm thinking steel or aluminum will have less internal friction, resistance, to fluid flow than neoprene or rubber. lines.
I'm not sure about PTFE, Teflon lined hoses internal friction
One way to find out is by doing a flow test in gear

A novel idea, a cooler flow test.

my old noggin is beginning to understand now !
thank you guys for helping me out !
the electrical circuit analogy made it click. also, the steel/aluminum tubing vs hose.
with the cooler flow test idea, i'm thinking comparing stacked plate to tube and fin ? if so, would/should the internals of the cooler be how much larger [size wise] than the in/out lines to the transmission ?

Actually you want to compare “ delta”. The difference between the output flow at the front cooler line fitting versus the return line entering at the trans.

Everything in between has a direct effect on the return volume. Pressure is a useless measure for this.

The less that comes back could have a negative impact on geartrain durability and a direct impact on stall.

is there an inline "flow meter" type of gauge one could use to check this ?
i still enjoy learning things i don't know, even though i'm old.

Most of the transmissions I tested (727,46/47/48) produced about a quart of flow at idle in less than 10 seconds, in neutral, at approx. 65-75 degrees.

That’s at the front cooler line fitting, one by the bell housing.

Works fine with the spare transmission in the car.
So on to the next problem.

So then the problem was inside the transmission which makes sense given the symptoms. The trans guy who looked at the trans and said it was okay must have missed something.

Yep.
Could be a casting issue.
The case is probably going to be thrown out.

I have seen the rear clutch pack slip and have the plates look good......but they were not. Usually only in high, or going into high. Were these ever really checked out?

Why would the rear clutch pack slip only in high gear? If it was slipping why wouldnt the frictions and steels show it? The rear clutch never begins its engagement with the input shaft spinning. So it is subjected to minimal slippage. If for some reason the trans was loosing pressure in 3rd only it should show in the front clutch. As far as the case itself. The passageway to the forward clutch feed isnt much over a 1" long. Pretty easy to see if its cracked. Its my feeling if there is no clutch damage that possibly the converter fill is being restricted or bleeding fluid internally. That would raise rpm and not show signs of slipage.
Doug