1936 Pontiac 8BA rear gears swap info

[aristech]

I want to know if it is possible to swap out the gears in my 1936 Pontiac 8BA. Factory is 4:55. Is there a cross reference to a better rear gear setup?

 

I am trying to keep original torque tube.

 

 

[Bob Shafto]

Two other rear end options were available. The "plains" rear end is 4:11. It will give you ±10% more MPG and run easier at highway speeds, but you'll probably notice the difference on moderate to steep hills, especially with passengers aboard (although the eight will help). I made the switch on my '36 Six and am glad I did. These parts interchange with Chevy rear ends.

[aristech]

Is there an identifier on the rear ends to know what gears you have or will I have to open up and look at the part number?

 

 

-aristech

[Bloo]

Look for a daub of paint on the axle shaft ends or on the bottom of the differential carrier. The mark will be rearward of the torque tube, but not quite all the way to the axle housing. If I remember correctly, plains gears are blue, standard gears are green, and mountain gears are yellow. You might just have to jack up a wheel and count turns on the harmonic balancer. Use high gear and take the spark plugs out so it turns easy. Its a two person job. Use flags made of tape to make it easy to count. Take the slack out before you start counting. I think you turn the wheel 2 turns.

 

Edited April 6, 2021 by Bloo (see edit history)