Pete Phillips Posted October 23, 2019 Share Posted October 23, 2019 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 Link to comment Share on other sites More sharing options...
Ben Bruce aka First Born Posted October 23, 2019 Share Posted October 23, 2019 Pete, I think the '37 is a complete different rear end. Ben Link to comment Share on other sites More sharing options...
39BuickEight Posted October 23, 2019 Share Posted October 23, 2019 I am fairly certain that won’t work. Link to comment Share on other sites More sharing options...
1937-44 Posted October 23, 2019 Share Posted October 23, 2019 I think you pretty much would need to change the ring and pinion. Not sure if a 1937-60 will work in a 1939-40. Link to comment Share on other sites More sharing options...
1939_Buick Posted October 23, 2019 Share Posted October 23, 2019 (edited) 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 October 23, 2019 by 1939_Buick (see edit history) Link to comment Share on other sites More sharing options...
MCHinson Posted October 24, 2019 Share Posted October 24, 2019 If it won't work, or you don't want to do the amount of work needed to make it work, I can help you find a buyer for the 1937 60 Series differential and related parts. 1 Link to comment Share on other sites More sharing options...
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