Rear Axle Ratio

[Saskwatch]

Would you help me decipher /confirm what these numbers mean the rear axle ratio is on this differential, please. 
A  37

1  44

 Thank you 👍

[Plymouthy Adams]

if you look at the numbers in terms of metric system it turns out to be a 3.9 axle 

[Saskwatch]

Thank you very much I appreciate it !👍

[Booger]

they used the metric system back then??? If the car was produced in Canada maybe so I see it as 3.7 -1 which was common

[TodFitch]

1 hour ago, Booger said:

they used the metric system back then??? If the car was produced in Canada maybe so I see it as 3.7 -1 which was common

About the only metric thing on the car is the 14mm spark plugs. Maybe the Shrader valves too but I am not certain about those.

 

The 144 an 37 are the number of teeth on the gears. Divide 144 by 37 and you get 3.89189 which is basically 3.9

 

They use teeth count that are not evenly divisible so that the wear is distributed across all of the gears.

[Saskwatch]

5 minutes ago, TodFitch said:

The 144 an 37 are the number of teeth on the gears. Divide 144 by 37 and you get 3.89189 which is basically 3.9

 

They use teeth count that are not evenly divisible so that the wear is distributed across all of the gears.

 Thank you very much for this , the numbers and their order really confused me but now it all makes sense!!

  This forum and the members here-in are the BEST. 👍👍

[Booger]

ok that makes sense to the numbers. and your basic Plymouth/Dodge bible specifies what year/model came with what axle ratio unless it was previously altered.

and if someone has a 3.54 laying around back of the barn....

[Plymouthy Adams]

I serious doubt any rear axle will be large enough of a carrier housing to allow a tooth count that great in number for the strength needed for the rear axle...size would be HUGE....and teeth count in a fine mesh to fit the housing, rip out on the first dump of the clutch.   IF you continue with the metric system and circumference of the gears...big circle into little circle., this is what I think is going on here....the tooth count is missing and only diameter is being used.

Edited February 22, 2025 by Plymouthy Adams

[9 foot box]

   A 3.9 gear ratio would have a 43 tooth ring gear and a 11 tooth pinion. See if there is a stamp on the top flat of the carrier. My U.S. differential is stamped 3.9 in both places. You can determine ratio by securing one wheel and rotating the other wheel one full turn, counting the revolutions of the pinion. It would be less than 4 revolutions for a 3.9 ratio. I’m not disagreeing with anyone, just additional information.