John Dirks

I would like figure out what gear ratio I have in my 76 Vette without tearing things apart.
Is there a reliable way to check a posi rearend while the car is in my garage?
Winter has hit hard here and I have to be able to do this in my garage.
(Another clean Canadian car tucked in for the winter).

63Banshee

Jack the car up so both rear tires are off the ground. Turn one tire so that the air valve is at apogee. Make one full revolution of the tire by hand while counting the number of times the drive shaft spins… you’ll have your gear ratio.


[Modified by 63Banshee, 9:46 AM 11/30/2001]

Neo Fender

And make sure the tranny is in neutral :)

63Banshee

And block the front tires.

noxqsz

John;

If you look on the bottom of the differential housing, probably near the center, laterally, and close to the differential cover, you'll see a stamped, two-letter code that identifies your differential ratio. You'll also see a stamped date code that will give you some idea whether or not you've still got the original differential housing. Best to take a small wire brush under the car with you to clean off the crud so you can get a good look. The codes you're likely to see are OA (3.08), LR-OD (3.36), OB (3.55), or OC (3.70). Use a bright light to look, the numbers and letters won't be easy to see. Of course, this is no guarantee, since what's inside the housing may have been changed since the outside was stamped, but it may be one more clue, in addition to the suggestions above, that will help you get an answer.

tnt76vette

Just go to smokemup.com......enter a few facts and figures and presto.....a gear ratio. No jackin up, no spinnin' wheels, and no need to count past 3.......... :D

63Banshee

Assuming your tach and speedo are accurate. When I first drove my ’64 GTO I thought it had 4.11:1 gears instead of 3.90:1 gears because of very small inaccuracies in the tach and speedo.

Other then removing the cover and counting gear teeth, doing the “spin test” is the most accurate way to determine gear ratio.