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1937 Century rear gears into a 1939 Special?

Pete Phillips

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I have a customer's 1939 Special in my shop. He wants a higher speed rear end so it will cruise at highway speeds without so much strain on the engine. I have a 1937 Century torque tube and rear end assembly, which should  be a 3.9 to 1 ratio. I know about the difference in torque tubes and drive shafts in the 1939 Specials. My question is, can we leave the '39 differential housing and torque tube in place, and just swap out the internal gears in the "pumpkin"? I realize we will have to remove the two rear axle shafts. Do I have to change out the pinion as well? Have any of you done this before? I have not.

Pete Phillips, BCA #7338

Leonard, Texas


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Ring & pinion must match. The only 3.9 that will bolt in is the 1939 series 60 (39 - 10 teeth).

1939 S40 4.44 ratio is 40 - 9  teeth

1939 pinion & its shaft is a 1 year only part for both S40 & S60.

A 1937 & 1938 ring (3.9 ratio) is same part number 1303405 as 1939 series 60 ring (39 - 10 teeth)

Have also seen a reference to a different ring part number for a 1937 S60

Drive shaft is pinned to the pinion shaft

No idea if a 1937 S60 pumpkin will bolt into a 1939 housing.

1940 went to a bolted torque tube / pumpkin connection. Before that is it riveted.


But a big risk/lot of work to take it all apart in the hope it will work.


If it works please let us know. 

Edited by 1939_Buick (see edit history)
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