69 rear axle ratio

[Tom S.]

I am trying to figure outb what gear ratio I have.MY chiltons booksays to look for a 2 or 3 letter prefix at the bottom surface of the carrier at the cover mountig flange.This is quite rusty, but I cleaned it very well AND still could'nt find any thing. I have a close ratio 4 speed, AND am doing about 3400 at 65 mph. I would like to know what I have becauseI don't want to turn this R.P.M. for any distance.If some one can tell me a more precise place to look I would really appreciate it.By the way it is a posi the tag is on the rear and also the sticker is on the storage compartment door. Thanks in advance.

Tom Stanton

[Chuck G.]

Re: 69 rear axle ratio

As a "rule of thumb" if you double your tach speed in 4th gear, with ORIGINAL diameter tires, you have 4.11 gears.

You could jack the car up, mark the driveshaft, rotate the tire one time, and count the revolutions of the driveshaft.....3 1/2 turns= 3.55 gears, and so on.

You should find the stamped numbers/letters and date where you're looking, but there is no guarantee the gears haven't been changed. Chuck

[Duke W.]

Re: 69 rear axle ratio

If you have the proper speedo gear setup for the installed ratio:

Revs@60/tire revs per mile = axle ratio.

60/65(3400)/775 = you do the math.

Duke

[Mike Cobine]

rear axle ratio calculator

Try this URL. Just plug in numbers to get the results you have.

http://www.angelfire.com/fl/procrastination/rear.html

For example,
3450 RPM
4.11 rear gear
1:1 final transmission gear
26 inch diameter tire
equals 64.92 MPH.

Sound close?




A MPH Calculator from RPM and Gearing