Many of us replace the rear end with a different axle. Why not just replace the Gears with the 3.38 units? Why go through the trouble for Posi rear. Is the 3.38 replacement gear good for the interstate, 75 MPH?
Not a simple question because you didn't state your rear tire size. My truck has 235x75x15 rear tires with a diameter of 28.5", so I'll use that to answer your question. With that size rear tire and a 3.38:1 drive ratio your engine would be turning 2989 RPM at 75 MPH. My truck has a 3.08:1 rear end, so at 75 the engine is turning 2723 RPM.
So! If my tires are 265-80 (16invh rims) (around 30 inches tall, and my stock gear is 3.9 ? Which is improved from the 1957's Improved for hightway driving? Then My RPM are lower? and would be even lower with 3.38?
30 inch tires and a 3.90 rear gear would = 3276 RPM @ 75 MPH. 30 inch tires and a 3.38 rear gear would = 2839 RPM @ 75 MPH.
2839 RPM's not to bad? Are the direction for the gears change detailed? Aslo thanks for all your help and infromation. Steve
