Torque Tube Swap
By Jim Merritt
Like a lot of old truck owners, putting a better gear ratio in your rearend to get higher speeds has crossed your mind . But, perhaps the high cost of those ring and pinion gear gear sets has put you off. Here's an alternative: Find a 1950 to 1954 Chevy car with a powerglide transmission (these cars were equipped from the factory with a 3:55 ratio) -- you will need the complete axle housing and torque tube. If you are changing to 5-lug wheels you can use the entire unit, or for 6 lug, discard the axle portion and use an axle housing (and axles) from a '48 or older pass car.
You will need to use the spring pivot type bracket and attaching hardware from the passenger car rear end. Cut these brackets off and relocate side to side and reweld, per the measured distance between your truck springs. Also, you will need to make an adapter plate/block to center the unit fore and aft on the springs.
The truck spring bolt is in the center of the wheel opening, but the passenger car spring bolt is located forward. This plate will need a hole on the bottom side to accept the round head of the spring bolt, and on top, another "round head" to fit into the bottom of the diff. pivot bracket, (like a lowering block).
This plate keeps the rear end from sliding forward and back. The height of this adaptor/block depends on how low you want your truck to sit. I've seen thick wall square or rectangular tubing used for this block. If you just bolt the unit in without this adapter, your wheels will be located too far rearward in your fender opening.
One word of caution, don't try to swap gear sets or any other associated parts from a car differential with a truck differential, they look the same but all parts are different dimensions. Only the propeller shaft/spline diameter is the same, making this swap work.
Any questions just send me a note.
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