1937 Ford rear axle ratio

9

91A-77B

Senior Member
I recently pulled the rear axle and replaced it with a Columbia. I want to sell it, and believe it's a 3:54 ratio. What's the best way to confirm the ratio?
 
On the bottom of the center banjo casting, the ratio... or tooth count is stamped. Yours should be stamped 39/11
 

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Big Deuce's advice does not take into account the real possibility of your ring/pinion having been replaced, and as a matter of fact, 3.54 was not a stock ratio in 1937. If the banjo and axles are out as a complete assembly, a positive confirmation would be to put a wrench on the pinion spline and turn it the 3.54 revolutions you believe to be your ratio, while one axle is stationary, the free axle will have turned two revolutions. On the other hand, if you have removed the axle housings from the banjo, just count the teeth on the ring gear.
 
This will give you a pretty good ball park of the ratio, which can be compared with known ratios (4.11, 3.78, 3.54) to see which one comes closest. For example, put a mark on the brake drum, straight up or down is convenient, then rotate the pinion or engine in high gear, 2 revolutions. If the brake drum mark indicates slightly less than one turn for the two pinion rotations, it indicates lower, higher number ratios such as 4.11 or 4.54.

DETAILS:

- Make a chalk mark on the bottom or top of the tire or brake drum
- Rotate the engine or pinion shaft clockwise exactly 2 revolutions.
- Measure the rotation on the tire or brake drum. It will be plus or minus one turn.
- Take this tire or drum rotation value, divide it into 1 (in other words, find its reciprocal),
- Then multiply it by 4.

EXAMPLE:

4(1/X) = 3.54
X = 1.12 (Drum or tire rotation value)

CLOCK BIG HAND INDICATION:

1.12 x 12 = 13.44 or about 10:30

A) Between 1 and 2 o'clock, ratio is 4.44
B) Between 12 and 1 o'clock, ratio is 4.11
C) Between 11 and 12 o'clock, ratio is 3.78
D) Between 10 and 11 o'clock, ratio is 3.54

GRAPHIC

581020
 
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A car that was originally a V8-60 came with a 4.44:1 ratio. I believe your car was a V8-60, but Al Lobsinger probably changed the rear when he restored it.
 
glennpm said:
This will give you a pretty good ball park of the ratio, which can be compared with known ratios (4.11, 3.78, 3.54) to see which one comes closest. For example, put a mark on the brake drum, straight up or down is convenient, then rotate the pinion 2 turns. If the brake drum mark indicates slightly less than one turn for the two pinion rotations, it indicates lower, higher number ratios such as 4.11 or 4.54.

DETAILS:

- Make a chalk mark on the bottom or top of the tire or brake drum
- Rotate the engine or pinion shaft exactly 2 revolutions.
- Measure the rotation on the tire or brake drum. It will be plus or minus one turn. Accuracy with these measurements is critical.
- Take this tire or drum rotation value, divide it into 1 (in other words, find its reciprocal),
- Then multiply it by 4.

EXAMPLE:

4(1/X) = 3.54
X = 1.12 (Drum or tire rotation value)

CLOCK BIG HAND INDICATION:

.12 x 12 = 1.44 or about 10:30

A) Between 1 and 2 o'clock, ratio is 4.44
B) Between 12 and 1 o'clock, ratio is 4.11
C) Between 11 and 12 o'clock, ratio is 3.78
D) Between 10 and 11 o'clock, ratio is 3.54
Click to expand...

excellent advice! better cannot be had!
 
Our 38 dlx buss coupe had alow speed gear, didn't know what till I had 3-54 gears installed bynthe coumbia guys in Tennessee; found out it was a 4-44,someone probably switched it, or maybe was for running these WVa hills, sometimes you can't see the numbers on the housing, to much rust
 
Richard, back when parts were available in junk yards, popular ratio differentials were quickly snapped up, while the left-overs were usually 4.44’s. Later scroungers had little choice. That’s apparently what had happened with both your coupe and with my convertible coupe.
 
Glenn, Thank you for your excellent description. My '34 rear end housing is stamped with only 9-3 with no final digit and I have been wondering what it could be ratio wise. I will do your test when I next can.
 

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Drain Oil.
Let it drip overnight.
Take a long skinny paint brush, reach in and put white paint on a gear .
With a good light , count the gear teeth till white mark comes back around.
 
The Art Doctor said:
Glenn, Thank you for your excellent description. My '34 rear end housing is stamped with only 9-3 with no final digit and I have been wondering what it could be ratio wise. I will do your test when I next can.
Click to expand...

Good!

3.54:1
11 ÷ 39
39 teeth (ring gear) ÷ 11 teeth (pinion gear) = 3.545 ≈ 3.54:1

3.78:1
9 ÷ 34

4.11:1
9 ÷ 37

4.55:1 ratio
9 ÷ 39
 
A video I made some years ago. No difficult maths involved.

https://youtu.be/bkvp3Fq21ZM

Notes:
You turn the hub exactly twice.
The other hub is locked, it does not turn.
The number of turns of the pinion = the gear ratio.

Mart.
 
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The Art Doctor said:
Glenn, Thank you for your excellent description. My '34 rear end housing is stamped with only 9-3 with no final digit and I have been wondering what it could be ratio wise. I will do your test when I next can.
Click to expand...

Since its a 1934 it will be 9-37.There was no 9-34 in '33,'34.
 
deuce lover said:
Since its a 1934 it will be 9-37.There was no 9-34 in '33,'34.
Click to expand...




I did assume it would be 4.11 if it was still stock inside having the 9 tooth pinion. But as this car has been apart before there is no telling what I will find inside. They messed with everything I have taken apart so far and it would not surprise me to find it was changed out.
 
You can put a 10 spline 35,36 3.78 in a 33,34 rear but the pinion bearing surface has to be machined to accept the 33,34 pinion.Then the driveshaft has to be shortened slightly. 3.78 was not offered in 33,34.
 
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