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Transmission converters have a charge and discharge circuit. The charge pressure is greater when the engine and transmission are working harder as when you are pulling a trailer. When the charge pressure increases the converter expands. Since the converter cannot move towards the front because the engine crankshaft and attaching flexplate are in the way the converter expands towards the rear. The converter hub slides into the transmission and consequently the front transmission seal rides on a different area of the converter hub O.D. Evidently the hub is marred or the surface may be rusty and the seal does not work as well at the loaded position as it does when the vehicle is unloaded or not pulling a trailer. I have seen converters expand up to 1/4 inch overall when subjected to a high load wide open throttle condition. That means that the hub is moving in and out, axial travel, in the front trnsmission seal by approximately that same amount. Since the converter is expanding the converter pushes against the engine crankshaft and the crankshaft moves against the crank thrust bearing and eventually causes the crankshaft bearing to wear and allow the crankshaft to move axially in the engine block. NOT GOOD. Also the crankshaft flexplate allows the crankshaft bolts to press against the front face of the convereter and in some instances the bolts will wear, brinell, into the front of the converter cover and result in a leak right through the cover where the brinelling occcured. The transmission is working harder when you pull a trailer it also uses a higher operating pressure. More pressure means more work and the transmission oil geats hotter. Hot oil in a transmission means shorter life for all components including the clutches, bands, seals, and bearings. The fix, if worth it, would involve a new converter that has a new and good smooth hub where the seal rides and a high capacity cooler installed after the radiator and before the transmssion. Since that configuration can cause cold weather starving of the rear lubrication system there are also a special "H' fittings and bypass valves for the cooler circuit when operating in colder climates.
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