Rear Axle: Optimum rear axle ratio

[jkresse]

I have a '53 Commander Starliner with auto trans. I'd like to slow the engine rpms down at highway speeds. What would be an optimum ratio for this car? The engine is stock and I'd be willing to put a first gear start valve body on the tranny. The stock ratio is either 3.5 or 3.55 (I forget which). I'm thinking around a 10% change to about 3.2. What ratios are available that will fit?
Thanks,
Joe Kresse

[JoeHall]

Both 3.31 and 3.07 Stude rear ends are fairly common. A 3.31 would give about a 6 1/2 percent reduction in RPMs at any given speed. A 3.07 would give about a 13 percent. Put another way, with 205/75 tires, a 3.54 will go about 56 MPH at 2500 RPM; a 3.31 will go about 60, and a 3.07 about 65.

If its an OEM, 332 CID motor, I doubt you'd want to go higher than 3.31. If its a 259 or 289, a 3.07 would be just fine. Second gear start in the tranny is OK too, but just don't look to impress anyone with burning lots of rubber on takeoff from stop lights.

I'd stick with a model 44 rear end, and avoid model 27.

[RadioRoy]

Hey Joe,

I live in Redwood City, too. Where is your car? I'd love to see it.

I agree that 3.31 would be the best. I changed my 54 from its original 3.54 to a 3.31.

You might want to double check the outer diameter of your tires also. The original ones were 7.10 X 15 bias ply and that same diameter crosses to P215-75R-15 radials.

if your tires are too small, engine RPM will go up.

Also be aware that there were almost no freeways in 1953 and no one was driving an SUV at 85 MPH on them, either, so your car was not designed for the type of sustained high speeds that are common today.

If your engine is not freshly rebuilt, 65 MPH is prudent, 70 is pushing it and 75 is kamikaze. That's just my opinion and a lot of the engine builders on the forum might disagree. A lot of folks who are new to old cars like to run them as fast as new cars routinely run.

Another thing that will contribute to under the hood noise is the fan. There are some quieter ones around.

[Swifster]

I'd leave the Dana 44 alone with it's 3:55's. I swap the transmission for a 700R4 or an early 4L60. You'll get first gear start and overdrive.

[DEEPNHOCK]

Gearing has a lot to do with local roads.
If you live in flatland, you'd probably want a lower numerical gear (higher ratio to be technically correct).
But if you live in a hilly area, then your choice of numbers might change a bit.
What has been said here is apt.
But, also think about your brakes.
Drum brakes on those long downgrades can make brake fade more of an issue.

It rarely is a simple 'one step' solution.
Changes beget changes.
Good luck with your project!
Jeff