"Tech Papers" by panic
Columbia 2-Speed Rear Axle Comments
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    The “Columbia” overdrive rear axle was available on Ford, Lincoln etc. pre-war. It replaced the right side of the original differential with a new housing and an overdrive sun and planet gear set operated by a vacuum piston. It’s called a 2-speed, but

Columbia rear axle Columbia rear axle cross-section Columbia rear axle Parts list

this isn’t accurate because the differential operates normally (no extra parts engaged) unless the overdrive set is selected (which can be in any gear, giving 6 choices with a 3-speed etc.).
    The ratios given were standard (ring gear tooth count divided by pinion gear tooth count) and overdrive (ring gear divided by pinion gear, times overdrive planetary ratio). According to the Ford literature, “2,713 RPM becomes 1,940 RPM”, which is .71.51% OD, but this does not match any of the owner’s comments. There are several separate planetary gear sets, as shown in the Parts list, but the exact ratios are not clear.
    The following comments were graciously provided by Clark, and originally appeared on the H.A.M.B. here: Columbia axle comments. Click on any of the pictures to see the full-size image on a separate page.

    “This isn’t a step by step guide to putting a Columbia together just a few snap shots as it went together. I thought people might find it interesting to see inside one.
    First of all why Columbias have a a reputation for being weak and problematic and how to overcome this. This is the spider side of the diff. You can see in the photo a

This is the spider side of the diff

seamless band that goes around the unit. From the factory the unit didn’t come with this. The whole thing has an open end with no support. What happens is when a great load is placed on the axle, for example dumping the clutch off the line, the diff wants to and does pull itself apart. When this happens the gears eventually start to climb each other and your left with a axle case of broken parts. Its a simple process to have the band fitted at a competent machine shop and this will give the axle a fighting chance of giving many trouble free miles.

    “The next problem area, again a simple design fault, is the other half of the diff that contains the planet gears. In the photo you can see each leg has a bead of weld around it. From the factory they only came tack welded and its not a great stretch of the imagination to see this not holding together for very long! Again a simple fix for a silly design flaw.

the other half of the diff that contains the planet gears

    This is the shifter assembly. It pushes and pulls the Columbia in and out of overdrive.

This is the shifter assembly

    This is the planetary gears set inside the axle casing.

This is the planetary gears set inside the axle casing

    The spider and gears go on over the top and the whole unit bolted together.

The spider and gears go on over the top and the whole unit bolted together

    The assembled banjo goes on next. This is shimmed just like a rebuild on a normal Early Ford rear. I decided to change the 4.11 gear set that the Columbia came with to 3.78 gears. The Columbia gives a 33.3% overdrive, so in top overdrive I should see roughly a 2.7 final drive.

The assembled banjo goes on next

    The finished axle.”

The finished axle.

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