72 rear axle ratio question

[flykelley]

Hi Guys
My truck has a 72 frame and components, took the rear axle cover off to find the gear ratio. It appears to be a 4:11. This is a part number off the ring and pinion. part number is #381778 11:4 GM Seems that a 1/2 ton two wheel drive long box would come with a 3:73 rear end.


Mike

[Stocker]

Different gear ratios could be ordered back in the day, not to mention changed by previous owners. Best way to know for sure, with the cover off, is to count the teeth. Divide the teeth on the ring gear by the teeth on the pinion gear to get the exact ratio.

[mitchell72]

You could jack it up, spin the drive shaft 1 revolution and see how much the wheels spin.

[67c10rustbuket]

Originally Posted by flykelley

Hi Guys
.... This is a part number off the ring and pinion. part number is #381778 11:4 GM


Mike

If you look a little closer I bet it says 381778 11:41GM on the ring gear. This means 11 pinion gear teeth, 41 ring gear teeth. 41/11= 3.73. The original gears had these part number/ratio stamping.

[flykelley]

Originally Posted by 67c10rustbuket

If you look a little closer I bet it says 381778 11:41GM on the ring gear. This means 11 pinion gear teeth, 41 ring gear teeth. 41/11= 3.73. The original gears had these part number/ratio stamping.

Thanks Dan, I thought a 4:11 was a bit much for a 1/2 ton truck. Ill have my brother check it out.


Mike