Hydromatic gear ratios

Lee ODell
Lee ODell Senior Contributor
edited January 2012 in HUDSON
It has taken me along time to locate the gear ratios for the 4 speed Hydra-Matic. I could not find that info in the Hudson Service Manual nor the Hydra-Matic Service Manual and other sources. I found it on Wikipedia - internet.

For anyone interested the Hydra-Matic 4 gear ratios are:

Automotive application
1st - 3.82:1
2nd - 2.63;1
3rd - 1.45:1
4th - 1.00:1

Light truck and other commercial applications
1st - 4.08:1
2nd - 2.63:1
3rd - 1.55:1
4th - 1.00:1

Reverse gear ratio??? I still have not found this information. I would like to know what it is. If anyone here knows the answer please let me know what it is. Thank you.

Have a good day.
Lee O'Dell

Comments

  • StillOutThere
    StillOutThere Expert Adviser
    edited January 2012
    It has always been my understanding that the gear sets used in the Hydra-Matics were matched to the torque, horsepower and "curve" charts of the engines they were mated to. Hudson drag racers in the '60s such as Ike Smith wanted Pontiac gears for example because they were more evenly spaced for optimum quarter mile performance than the huge 2-3 shift rpm drop provided by the Hudson gears. I remember watching Ike installing a Pontiac gear set into a Hudson case so the tag on the outside still indicated a genuine "stock" Hudson transmission. Surely the same gears were not behind a Kaiser with a Continental flat head six and Hydro as were behind a big Cadillac V8 and Hydro as further example.
  • Lee ODell
    Lee ODell Senior Contributor
    edited January 2012
    It would seem logical there would be multiple gear sets for different vehicles but I have not found any information to verify that happened. That is what I am trying to find out. To the best of my research I have only found these two sets of gear ratios. GMC trucks were sold by Pontiacs so it is quite possible the 3rd gear from the truck was put in the Pontiac. Or Ike may have used the truck 3rd gear. The Hydra matic became available to the GMC 3100 truck in 1952 and Chevy trucks in 1954.

    The Hydra-Matic was used first in 1940 Olds then Cad. It was in Hudson, Nash, Frazer, Kaiser, Willys, Lincoln, and Rolls-Royce through 1967 another source said until 1978. Also, in military vehicles, even tanks. But I have not seen any other gear ratios. There may have been different size couplers? and different oil pressures, valve bodies or whatever to control the shifts for different HP and vehicle weights. I'm no tranny expert. When B&M built the Hydra-matic for my race car in 1963 they wanted to know everything about the motor, car weight, gear ratio, tire size exhaust system, supercharged or not and if it was for street use or race only to set it for its intended use. I do not remember what the gear ratio they ended up using in my car. I suppose GM did the same thing to make it work for different vehicles. Also, differential gear ratios may have been factored into the equation.

    If anyone knows of any other gear ratios I would be interested in knowing what they are and in what car they came in.

    Thanks for any imput.
    Lee O'Dell
  • StillOutThere
    StillOutThere Expert Adviser
    http://ateupwithmotor.com/technology/246-hydramatic-history-part-1.html?start=2
    has another ratio chart for you.

    http://www.earlytimeschapter.org/1952.html is a relevant Pontiac discussion article but internal ratios are not mentioned.

    Get into "notes" about 82% down this page for another group of ratios.
    http://www.matadorcoupe.com/trannyspecs.htm
  • Lee ODell
    Lee ODell Senior Contributor
    edited January 2012
    StillOutThere wrote:
    http://ateupwithmotor.com/technology/246-hydramatic-history-part-1.html?start=2
    has another ratio chart for you.

    http://www.earlytimeschapter.org/1952.html is a relevant Pontiac discussion article but internal ratios are not mentioned.

    Get into "notes" about 82% down this page for another group of ratios.
    http://www.matadorcoupe.com/trannyspecs.htm

    Thank you for the information. Every bit helps.

    Link 1 has an interesting Hydramatic chart on front and rear planetary gear ratios I haven't seen before and that pre war hydromatics gear ratios are:
    3.66:l, 2.53:l, 1.45:l and 1.00:l

    Post war ratios are:
    3.82:1, 2.63:1, 1.45:1, and 1.00:l

    All the other sources seem to be carbon copies listing the post war ratios being used in the first production Hydramatics in Oct 1939 for the 1940 Oldsmobile. Thanks for the claification.

    I didn't list the ratios in link 3 before because they are used in Jetaway Hydramatics:
    3.96:l, 2.55:l, 1.55:1, 1.00:1

    Is it possible Jetaway Hydramatic planetary gear sets are innerchangable with Dual Range Hydramatics?

    Thank you and have a good evening.
    Lee O'Dell
  • StillOutThere
    StillOutThere Expert Adviser
    I wonder if anyone else has interest in this topic considering the dirth of additional comments. Thanks for your work on it Lee.
  • Snailslayer
    Snailslayer Expert Adviser
    edited January 2012
    I have interest in this topic. I just looked through the Hudson Hydramatic manual as Lee said he did too and sure enough, 196 pages and not 1 gear ratio listed. thanks for posting the info.

    Edit. 700r4 4th is .70:1
  • akcoop
    akcoop Administrator
    edited January 2012
    I found a place online that said the 700R4 has a fourth gear ratio of .7:1

    Here is where I found it:

    http://www.smokemup.com/tech/700r4.php
  • brumac
    brumac Expert Adviser
    All,
    I have a note that I wrote to myself some time ago that says the 6 cyl? (maybe Pontiac) first gear ratio is 3.98:1 and the 2,3 and 4 are the same as pre 1956.

    Bruce
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