Selecting and swapping differentials

September 1, 2017 | By Staff


In the June edition you advised a man to check out Kaiser Willys Auto Supply for a ring and pinion gear for his 1940 Willys. Like you, I have a 1940 Packard. Mine is a touring sedan. I love the car, but driving it on the freeway is worrisome. In your response to the Willys owner, you indicated you swapped out the differential in your Packard. Did you get the necessary parts from Kaiser Willys Auto Supply? If so, which set did you order for the Packard?


Kaiser Willys doesn’t carry Packard parts. What I did was install an original Borg Warner overdrive in my 1940 Packard 110 coupe, but then I left the nonoverdrive original differential in place because it has a higher (numerically lower) gear ratio than the one that was generally used with the overdrive. That combination makes it possible for me cruise at 70 miles per hour, though stopping is a challenge at higher speeds.

Junior Packards generally used the same rear ends in their smaller models up until 1952 and a 3.90:1 ratio, which would be ideal, was available later during those years. Check the bolt pattern of the pumpkin and verify the ratio before laying your money down. You may also have to change the rear universal joint yoke to accommodate the new differential.

The easiest way to change the gearing is to swap out the whole pumpkin, gears, carrier and all. But if you are only able to obtain new ring and pinion gears, I advise that— unless you know how to do it—you have the new gear set installed by a pro who has the tools and the experience required to do it right rather than attempting it yourself. Differentials require precision when it comes to gear mesh, contact and bearing pre-load.

Packard made their own rear ends, but gear sets may still be available in the ratio you need from after-market manufacturers, though I am sure they would be expensive. Never try to replace just a ring or pinion gear alone because they are machined in matched sets. The best option today would to get a different rear end assembly from someone who is parting out old cars or has one squirreled away somewhere. You could also try:

Max Merritt Packard Parts and Accessories 235 Terre Haute St. Franklin, IN 46131 Orders: Inquiries: