Sounds like Hydra-matics are getting a bad rap due to time issues more than anything else.
Two main reasons a Hydra will shift hard:
1. Worn out or loose tranny mounts.
2. New reproduction tranny mounts.

#1 is self-explanatory. If you have original mounts in a car that is 60+ years old, they are not going to be in the best of shape, even if the car was garaged all it's life. Excess movement is not only dangerous in the transmission, it causes it to move around too much and throw the car around and give some "hard" shifting.

#2 is a little different. New reproduction tranny mounts have modern day vulcanized rubber which is as hard as a hockey puck, or at least as hard as a super ball. Too hard. The originals were WAY softer and spongier and had a certain amount of give to them to soften the shifts. New reproduction mounts are noticeably harder shifting.

Usually, internal tranny problems are going to give you much more than hard shifting, if the car engages at all. Also, the TV linkages have to be set up properly for the transmission to act in harmony with the engine. If it's not set up properly, it won't act properly.

Russell,

Thank you for the explanation.

So if I understand correctly, these transmissions "shift hard" all the time, but with new rubber mounts it is absorbed to the point you don't feel them jerking into gear?
I can see how if the mounts are worn or broken it would cause vibrations from the engine and transmission to be transmitted to the steel frame and on to the driver.
I noted too, that if I accelerated slowly, as opposed to a bit more accelerator, the shifting was smoother.

Rob

Did you buy a car?

This is on a car I was test driving.
I drove another car yesterday that shifted so smoothly that it almost felt like a modern car. It did have new mounts.
Rob

Engine tune & idle speed have a definite influence on the shifting pattern. Most modern day mechanics tend to set the idle speed too high which will influence the "HARD" shift to a great degree. Yes, and the trans mounts need to be just right. My '54 was really shifting super hard, but by gently massaging the linkage from the accelerator to trans valve body, and adjusting the engine idle correctly, I have all but eliminated the "HARD" shift situation.

Jerry,

Thank you for sharing your experience.

Rob

Jerry,
If the transmission is shifting too early.. Which way do you adjust the rod? Under normal throttle pressure, Mine is in fourth at 30MPH.

My '51 Hornet (many years ago) made what felt like a very hard shift if I floored the gas pedal to start off. I finally discovered that the front motor mounts had lost their tensile strength, because the top side of the rubber was no longer bonded to the metal. The result was that with full throttle, the engine would rise a couple of inches above one front motor mount and then come back down when I eased up on the pedal, which was when the transmission shifted to second gear. The jolt of it coming down onto the mount felt like a "hard" shift! If I didn't start off so fast, everything felt normal.

Dave, if it's shifting too early, the control rod needs to be lengthened. As alluded to above, the adjustment is very sensitive. Turn the turnbuckle just 1/2 turn at a time, drive testing it between tries.

Park is spot on. It might seem like a never ending chore,but the feeling of accomplishment when you are satisfied with the outcome is quite gratifying .

Thank goodness I don't have trouble with mine! #GusSouza

Thank goodness I don't have trouble with mine! #GusSouza

I've already spoken with Gus about the transmissions and pulling my trailer. He says I should be fine, but if not he'll build me one with custom shift points and heavy duty parts to suit the trailer.
Nice to have that option!

Rob

No matter how well the transmission is built, The state of engine tune and external linkage adjustments can make a good transmission appear to be bad.. Think about it. If one turn of a fine thread rod can make a difference. imagine the engine moving forward or backward just a quarter of an inch ! The HydraMatic manual has a detailed adjustment procedure for setting it up, then you have to make fine adjustments to suit the car.
One of my complaints with some HydraMatics is the rough down shift. For some reason, mine does not have that problem. I recall a 54 Pontiac and a 54 Hornet that was difficult to make a smooth stop with power brakes and the car lurching. Fortunately my rebuilder ( now retired dang it) must know how to keep that from happening.

Dave,

Thanks for the thoughts!

That sure makes sense.
It is scheduled to go on the lift tomorrow so we can get a better idea of the condition of the mounts, linkages, and underside items.

Rob