[zjosh27]

Any thoughts on a good performance set up for the rear axle.

I you might have guessed I new at this restoration stuff.

My thoughts are from all that Ive read is

9 inch traction lock with 3:50 gear ratio and with a good set of tires.

I want performance for the street. But I also will do some long distance hwy trips.

I read that a 4:13 was bad for highway driving

I have a 351 Windsor that is being build with better heads.

I have an FMX trans, looking to put in a C6.

[66GMC]

From the other thread, we have detrmined that you *probably* have a 3.00:1 ratio ... provided that it is still all original.

There are online calculators that will give you your engine RPM at a given speed ... but you will have to know the tire diameter in order to get the correct result.

This page has a whole bunch of related calculators, including one that will give you your tire diameter from the metric tire size (i.e. P225/60-R15 = 25.6" tire diameter)

So using that tire diameter and your proposed 3.50:1 gear ratio as an example:

MPH = 60
Axle Ratio = 3.5
Trans Ratio = 1
(all 3-speed automatics have a final drive ratio of 1.00:1 ... or "direct". An overdrive A/T would have a final drive ratio of about 0.70:1)
T.Case Ratio = 1 (You don't have a tranfer case, so leaving it at 1 = no effect)
Tire Diameter = 25.6
Push [Calculate] button to obtain the resulting RPM ... 2756

At 70 MPH, with the the same tire size, the resulting RPM is 3216.

[OneMoreTime]

I think in this particular case I would be looking at a 3.23 gear..that should launch fairly well and be a better cruiser..

Sam

[big gear head]

The '66 Fairlane GT came with 3.25 gears. I haven't seen many trucks with 3.25 gears, but I have seen many trucks with 3.50 gears and the Trac Lock differential. You are going to have to figure out if you have 28 or 31 spline axles before going any farther. You also need to be sure that you have the 9 inch rear end and not the 8 inch rear end.