Gear ratio question

Lklemm1Lklemm1 Member
in HUDSON Posts: 47
I have a 47 pickup and don't know the rear end gear ratio. Does anyone know what was standard in the trucks? What ratios were used in 1947 cars? I am looking for my best ratio for some highway traveling. I may want to look for a different rear end for truck. I persume that what I have may not be great at highway speeds. Running a 232 flathead.


  • PerPer Member
    Posts: 147
    The usual ratio for cars was 4.11 if no overdrive.  4.58 if overdrive.  The trucks may have had a stock ratio of 4.58 without overdrive.  

    Many years ago I put an axle from a 1969 eight cylinder Ford Mustang in a 1942 Hudson.  It had a ratio of 2.78, and was wonderful for highway driving, but I never got out of 2nd gear in local driving.

    Since you have the short stroke 232 engine, if you have the 4.11 axle, its not too bad, and is very good if you have overdrive.  I presently have a 1949 Hudson with a 232 engine, overdrive, and 4.11 axle.  This works very well for highway driving.  I've made two round trips across the country (Massachusetts - California) recently.

    You can determine the rear end gear ratio:  Jack up one rear wheel of your truck.  Put the transmission in neutral, and the hand brake off.  Make a mark on the driveshaft, and a mark on the tire.  Rotate the wheel by hand exactly two revolutions.  As you rotate the wheel, count the revolutions of the driveshaft.  
  • Jon BJon B Administrator
    Posts: 6,445
    You could install a Hudson overdrive transmission (which would give you the most flexible system for shifting into the right ratio) or a rear axle for a better rearend ratio.  With the 262 StepDown engine and bellhousing, you may have to be careful which OD and trans. you use, since you are putting a later trans into an earlier car.  But I'm sure there is a way to do it.

    The nice thing about dropping a complete rear axle in (say, from a 60's MoPar or Mustang), is that you could always remove it and put the original rear axle in if you ever wanted to go for authenticity. 
  • ValVal Member
    Posts: 446
    I believe a later trans will work but as Jon said be careful. I am having a 1950 O/D trans put in my 39. I am told that it will barely fit in the car and have to use a different bell housing.   Dr Doug and the gang are doing it. You may want to contact them if you go that route 
  • stbrysonstbryson Senior Contributor
    Posts: 101

    According to the 1947 Hudson Price, Equipment and Option Folder, standard gear ratio for 1947 Hudson pickups was 4 5/9.  For cars, standard gear ration was 4 1/9; 4 5/9 was optional.  The standard ratio with overdrive was 4 5/9, while the optional ratio with overdrive was 4 1/9.

    I understand that one way to get a different ratio would be to install an overdrive unit.  Would it be possible to change the ring and pinion in a truck to the 4 1/9 ratio?

    Take care,

    Steve Bryson
  • Jon BJon B Administrator
    Posts: 6,445
    Certainly.  I have seen N.O.S. ring and pinion sets for sale at Hudson flea markets.  Or, you can just buy a complete used axle with the 4.11 ring and pinion already installed, and bolt the whole thing in.  When you use the 4.11 rearend in conjunction with the overdrive, you will have the best highway ratio possible.  Normally, with the stock 3x5 splasher engine (around 100 HP) this might be a bit of a strain on the uphills, but with a 232 you have more horsepower.  So unless you live in mountainous territory the 4.11 + overdrive would probably work just fine.
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