IF the rear end is from a 55 - 57 Chevy then the axle ratios offered were 3.36, 3.55, 3.70 as shipped from the factory depending on the engine / trans combo. Dealer installed 4.11 and 4.56 ratios were also available. That exact axle with a pumpkin was used right up through 1964 but starting in 1958 Chevy used coil springs in the rear so the bracketry had to be removed and leaf spring pads welded onto the tubes to use one in an earlier leaf spring car. That's why the 55 - 57 rears are the most commonly used in the pre 55 cars. The 58 -64 axles had a variety of ratios from 3.08, 3.23, 3.36, 3.55, 3.70, and 4.11 again depending on the year and the drive train package or how the customer special ordered the car.
One thing you didn't mention was whether or not the car has a conventional open drive shaft or is still using the torque tube. The torque tube rear ends also bolted in from the front and some even had a removeable rear cover as well. The 55 - 57 axle uses an open driveshaft. Your original 50 axle was a torque tube set up.
I have no idea exactly which ratio you may have but running a TH350 with any of those gears will work ok. The 3.70 might be a little stiff for highway driving but the 3.36 and 3.55 are good all around ratios and 19 points difference in ratios amounts to about 200 rpm difference at highway speeds, hardly worth worrying about.
4.11 and 4.56 are not highway gears unless you have an overdrive trans.
Mike G ( 4355 )
