Classic/Antique Car Repair/rearend gear ratio


Hi Brad,

I have a 1940 Hudson Super six. I am thinking of changing out the rearend to a higher gear ratio. As I understand by doing this I will be able to drive my car at higher speeds without the hearing the whining noise from the lower geared rearend.

I have heard that I can switch out a Ford Explorer rearend because the width is the same. My question is how do I measure that? from hub to hub? What do you recommend that I do?


There are several dimensions that need to be considered. The first is from spring saddle to spring saddle. These are the mounting points where the rear springs rest and the spring U bolts hold the axle housing in place. If the dimension is not correct it is no big deal to have a welding shop cut them off and re-weld them in the correct position. The overall dimension from hub to hub is more important as you don't want the wheels sticking out or in too far. Some variation can be overcome using a different wheel with a different hub offset. Now in changing the ale ration to give a slower engine speed at high speed will also change the low speed characteristics of the car. Low end torque, off the line performance will be significantly reduced. You will have to shift from high gear to a lower gear at a higher road speed. You will have to run a bit higher road speed before up shifting from first to second and second to third. So what you will gain on high end you pay for on low end performance.

Classic/Antique Car Repair

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Brad Sears


All automotive including antique and collectible. However if the car has been modified I can only answer in general terms and maybe get you pointed in the right direction.


Automotive tech instructor. Syndicated auto columnist 1970's though the early 1990's. Syndicated auto radio talk show, Ask Brad About cars, CBS Radio 70's through 90's TV Show "Last Chance Garage" 1980's PBS-TV syndicated. Auto instructor for the following companies: Fram Autolyte Holly Carter AMF Ford Motor University Of Conn Blue Hills Technical School Sugar River Technical Center Grew up in a family garage in Needham Mass and turned wrenches from the age of 14.

Manchester Union Leader, Nashua Telegraph, Motor Service Magazine, Yankee Magazine, Popular Mechanics (Saturday Mechanic early 80's), Los Angeles Times, New York Times, and lots more.

More than I care to remember. Basically Franklin Technical Institute in Boston, Northeastern University, Fitchburg State Teachers College, Tufts University, and a lot of factory schools along the way.

Awards and Honors
Moto Award winner. And much more.

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