Stopping a chronic leak (TorqueFlite 727)

[70Challenger440]

I have dealt with a chronic transmission leak from the pan for decades with my Torqueflite 727 (1970 vintage & 440 engine). The trans has been checked and rechecked, rebuilt, resealed, multiple STOCK capacity pans tried, and various types of gaskets and sealants both of older and newer styles, etc. I even tried the start in neutral trick  which did help 'somewhat'. But the trans still leaks terribly eventually from the pan.


An old timer into these cars suggested the cause ... and a solution. It may even sound crazy but I already tried everything else. He suggested that he has stopped the issue on his cars, by switching to a higher capacity pan that is aluminum.  (B&M_10280). He blamed his leak on the inevitable converter draining and the pressure caused by it on the oil pan gasket. He says since the deeper pan allow for 4 extra quarts and repositions the filter lower to the bottom of the deeper pan,  he can run his trans  2 quarts low, yet still has 2 quarts more than with a stock pan. He claims this allows the converter to drain without causing a leak nor any damage to the transmission when using since there is still more than the required fluid amount to operate correctly.

Since I already tried everything else over decades, I am willing to try this, unless someone here convinces me it will cause harm to the transmission. Your thoughts?

[Katfish]

I'd bet it's not the pan.
I fought same issue for years, first it was the shifter seal, then the pivot pin.
Both of these slow drip down and make it appear the pan is leaking.
I changed my pan and gasket multiple times.

[71GranCoupe]

 I seen an instant where the pan had been over tightened causing an uneven surface around the bolts, thus a good seal was not happening. Also the seals for shafts as shown are also a notorious place for leaks.

[70Challenger440]

Thanks , but as stated, the transmission has been rebuilt once and then resealed twice by shops familiar with vintage TorqueFlites. They changed everything multiple times and even after bringing the car back for follow-ups, it still leaks terribly. At this point, I am accepting I need to seek a "workAround" as I believe this transmission will otherwise always leak otherwise. I am looking instead to reduce it's internal pressure on the gasket. (by using the recommendation I was given in my original post above).

I am ready to try what I mentioned above (IF I can be assured by those here) it will cause no  mechanical harm to the transmission when driving.

[7212Mopar]

I fixed mine a few months back. Transmission was fairly new so not leaking at the shift pivot shaft or the kickdown valve. I overtightened the neutral safety switch splitting the black plastic from the metal, cracked the plastic and also have some leaks with my high capacity TCI aluminum pan. Fix was apply some sealant to the gasket and thread of the neutral safety switch and not overtighten it. Found my aluminum pan was not perfectly flat so I use sandpaper on a flat surface to get it flat, check with straight edge. I then used the modern Lubelocker gasket install without applying any sealant. The pan was put back with locking fasteners so it does not get lose, tighten in pattern evenly by hand and torque to 15 to 20 inch pounds (forgot exactly). Filled trans with synthetic fluid to bottom fill mark when trans is running in neutral and hot. Not a drop on the floor since. I do have a very small oil leak, likely from the crankshaft end seal. It could be normal. Many had said if it does not leak it is not a Mopar. I don't like that.

[mopar jack]

Had problem with leaks at the usual places, oil fill tube, shift linkage seals, speedo seal and more. Got serious and cleaned the bottom of the transmission to eliminate any oil residue then drove the car and checked for leaks. I sealed eveything but the pan kept showing up wet I concentrated on it and finally noticed a defect in the pan that shows on  3 of my spares. See attached: the pan has a weak spot that causes it bow slightly and allow fluid to weep out. I took a small piece of angle iron and bolted it across the weak area and no leak.

[Chryco Psycho]

If the car sits a lot over time the converter will drain which overfills the body of the trans thus it will leak , if it is started regularly the converter stays full , no leaks !

[70Challenger440]

If the car sits a lot over time the converter will drain which overfills the body of the trans thus it will leak , if it is started regularly the converter stays full , no leaks !

True ....  and this is what was mentioned in my original 1st post that I had been told. He explained how the 'temporary' excess fluid then puts pressure on all the gaskets and seals causing leaks. He told me to get a deep aluminum B&M trans pan,  and then (since it gives 4 quarts of extra capacity), to fill it 2 quarts low, (which is still 2 quarts more than with a standard pan). He claims this instantly solves the problem because it's just not a good idea to start a vintage car every few days unless you plan to actually drive it that day and get it up to temperature.

I want to try this solution that is claimed to give the extra internal space for the temporary excess fluid ...  so the ONLY question I have been trying to get an answer here  is .... Will what he suggested cause mechanical damage to the transmission when driving it?  (2 quarts underfilling on a deep pan that adds 4 quarts extra capacity). I assume not since the pickup&filter is then moved to the bottom of the deeper pan. Hopefully someone here can answer this before I try it.