After Firing up a newly restored 1952 Coupe we had a profuse transmission fluid Leak from Front of transmission. We. had to pull it apart and discovered the front pump seal was fine. The leak was from between the 1955 crank spacer and flywheel. Jack Clifford previously provided a product for sealing the Hudson automatic transmissions flywheel to the crank. That sealer was made by Goodyear, and called Polybond. The sealer is no longer being made. A call to Hydro expert Gus Souza resulted in his recommendation to use number 1 Permatex Gasket Sealer. When using this sealer assure you use a heavy application in the alignment pin area. Do Not Add Fluid to your transmission for at least 8 hours This sealer type must harden before it will seal properly.
The 51 and early 52 Hydramatics used on Hudsons, like all other Hydramatics of that vintage were 4 speeds. 4th was direct drive, NOT overdrive. What is different on the late 52 through 54 hydramatics on Stepdowns is the later ones were set up so you could lock out 4th gear for hilly or around town driving, and this newer setup was called "Dual Range Hydramatic". The Dual range had a different shift quadrant with detents for "4" and "3" in addition to the "N" "Lo" and "R". In the Hydramatics, when engine is shut off, the "R" position is used to keep the car from rolling. You should always use the hand brake as a backup. On the early Hydramatics (1938-50), the Reverse pawl was more vulnerable to damage if the car was bumped while parked, or if one tried to engage reverse while car was still moving forward. The reverse pawl was redesigned with a cone clutch for 1951 to address this issue on the later Hydramatics.
The shift points are controlled by a centrifugal governor, and the speeds of these shift points can be adjusted by adjusting the throttle rod that runs back to the transmission from the throttle bell crank at the left rear of block. Shortening this rod makes the shifts occur at higher speeds, lengthening makes the shift occur at lower speeds. In your case, the rod may be too long, but then you say it downshifts harshly. The harshness/ softness of the shifts can be adjusted by changing the bands/ clutches and hydraulic pressures, but the proper tools and know how are needed. Almost all these adjustments can be done outside of the transmission itself. I advise you to check the fluid level first! Low fluid level can cause harsh and erratic shifting. An indication of low fluid level is this: if when starting the car in neutral, the car "jumps" forward upon starting, this is often due to low fluid.