1956 Pontiac

Hi All,

Is there anyway to find out what rear gearing is in the rear differential of a 1956 Pontiac without taking the cover off?

Thanks for any help

Jason

If you have a car with a posi or limited slip rear, jack up the car and get both rear tires off the ground. Now put your jackstands under the axle. Make a line on the pinion yoke and onto the rear end with chalk or a grease pencil. Do the same to the tire on the car, so you can see when the tire has rotated exactly one turn.

Now count the number of turns of the driveshaft that it takes (use your chalk marks) to make the rear tire turn one complete rotation. (Transmission needs to be in nuetral or out of gear.)

If your car has an open rear, jack up only one rear tire and leave the other on the ground. Now put a jackstand under the lifted side. Turn the tire and again count the number of turns of the driveshaft, but this time you must turn the tire two full rotations.

So:

Posi: Jack both wheels off the ground. Turn one wheel 1 complete turn.

- Count the turns on the drive shaft.

Non-posi: Jack one wheel off the ground. Turn the wheel 2 complete turns.

- Count the turns on the drive shaft.

If it takes about 2 and three-quarters turns, it's around a 2.73 gear ratio. If it's a little more than 3, you have 3.08s. If it takes about 3 and a quarter turns of the driveshaft, you have 3.23 or 3.25 gears. Very close to 3 and three-quarter turns, 3.70 or 3.73 gears. This method won't work very well on a posi that's worn-out and won't spin both tires equally.

Thanks!!

Here are the codes stamped on the diff.

1956 Code

3.08 0

3.23 9

3.42 8

3.64 6

3.90 4

Here are the codes stamped on the diff.

1956 Code

3.08 0

3.23 9

3.42 8

3.64 6

3.90 4

you'll find that looking at the 7 o'clock position on the rear end housing, a square looking pad where the single digit number is stamped, most likely you'll find a 0, 9, or 8.

charles coker

1953 pontiac tech advisor

tech advisor coordinator

pontiac oakland club int'l