Reproduction Parts for 1916-1964 Chevrolet Passenger Cars & 1918-1987 Chevrolet & GMC Trucks


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Joined: Feb 2014
Posts: 61
Shade Tree Mechanic
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Shade Tree Mechanic
Joined: Feb 2014
Posts: 61
i have a 31 chassis we are building into a great race car. we want to retain the rear mechanical brakes but want to go to open drive. does anyone know of either a conversion kit to make the closed drive prinion to open drive with a yoke, or does anyone know of a later chevy center section such as 55 and up that will go into the 31 housing and if so are the axles from a 31 go into a later center section

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Joined: Sep 2006
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You are probably setting yourself up for a lot of frustration. The original 1931 six cylinder engine has a nominal 50 horsepower. The '31 model and its predecessors were nefarious for breaking axles if caution is not taken. Anything more than 50 hp will probably result in a series of broken components. In talking with other long time members we feel that the broken axles and drive shafts we have seen appear to have been at least partially cracked already. Looked like it had happened in the heat treating cycle, as in it was mostly already a rather old crack. Chrome molly axles were available for awhile, and may be still, but are $300 + apiece.

The model a crowd has conversions that can modify the original rear end into an open drive shaft and a S-10 5 speed installed against a modified 4 cylinder engine bell housing. That type set up or similar with an original '31 engine should result in a nice driver. Many people have welded Borg Warner overdrive assemblies into their original torque tube drive shafts. If you are changing the engine, once you start cutting it up - it is no longer a unique automobile but rather just another hot rod. The experiences, the adventures, and the stories just go away.

Contact anyone who has participated in an "Early Six Cylinder Tour" and they will tell you wonderful stories that are hard to beat.

I know several people with the overdrive assemblies but they do not get excessive with the speed (55mph) because the mechanical brakes fade sooo quickly at the higher speeds.

Keep us posted as to your progress.

Art

Joined: Dec 2016
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Oil Can Mechanic
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Oil Can Mechanic
Joined: Dec 2016
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What you ask for doesn't exist. There are a whole host of reasons why it can't be done easily like it can on a model a. That's why there is no kit. I don't want to rain on your parade, but even if the pumpkin bolt pattern is the same as something later (possible), there are other things that deserve more of your attention. I'll start with two. I would encourage you to crawl under your car and imagine how you would deal with these 2 things, and whatever other changes you would have to make as a a result of them. That would be a good start toward understanding exactly what you are up against.

Firstly, the rear axle is not solidly attached to the rear springs on old Chevrolets. It is sort of like a bearing or hinge. When a wheel drives the car, the reaction force is taken by the torque tube, which acts as a giant lever. If the torque tube were not there, the axle would wind up and rip the driveshaft out. You would have to change the way the axle mounts to the springs from hinged to a solid mounting. That makes using an original housing less attractive. Also, the springs will now be taking the torque reaction force where they didn't before. They were not made for it. On 1950s era Chevrolets, some people have got away using the originals. I wouldn't count on it. There is a good possibility you might need custom springs.

Secondly, the torque tube in a Chevrolet runs dead center in the car. On an early car like this, the torque tube comes out of the center of the pumpkin. A hypoid axle has the torque tube or dirveline coming out down and toward the right. Chevrolet kept the driveline dead center when they switched to hypoid in 1937 (cars) and 1940 (1/2 ton). This means in the new designs that the "bulge" in the axle housing that the pumpkin bolts to, and the pumpkin itself had to move left to keep the driveline centered. Now the axle shafts are 2 different lengths, negating any idea that your axle shafts would work in a later housing, even if the splines happened to fit. If you got a newer open-driveline pumpkin to fit in the old housing, the driveline connection will be down and to the right. The driveline will be running skewed in the car. That isn't necessarily a dealbreaker, as long as it doesn't hit anything. I am not sure about 1931, but on a lot of Chevrolets it would hit the frame.

In my opinion, if you must do this, you would be lots of money, time, and frustration ahead to use a whole later axle, and figure out what it would take (probably custom axle shafts and some fabrication) to get your wheels and brakes attached to the newer axle. Good luck on your Great Race campaign!

Last edited by bloo; 06/27/22 11:14 PM.

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