(Writes with quaking hands)
ROB, I THINK YOU'VE FOUND THE CHEV HALF-TRACK!!!!
The wheel discs are NOT the same as those on the 1 ton Tracked Truck, and that was fitted with a C15 rear diff. The wheel discs appear exactly the same as those in the half-track CMP pics.
As Bob and I discussed at Corowa, the rear axle with the Carrier drive sprocket MUST have a different gear ratio to the Chev CMP front axle with 10.50-20 tyre if this vehicle is to be driven with the front axle engaged. The circumference of a 10.50-20 tyre is approx 128inches. The Carrier track has a link pitch of 1 3/4in, and the drive sprocket has 35 teeth, giving a sprocket circumference of 61 1/4in. We know the front diff of a C60L/S is 7.16:1, so for this vehicle to have the same track ground speed as the front tyres, the rear diff ratio needs to be approx 3.40:1 ratio. Ford didn't make this ratio in the truck sized gears, but DID make this ratio in the 3/4 ton commercial. That drive flange is the same as the type used on the taper type pinion (compared to splined), which co-incidentally is the type on the 3/4 ton commercial!
Rob, can you do us all a favour? Hit the rear part of the diff with a wire brush above and below the fill plug. Look for stamped numbers like 10 34 or such.
If you find nothing there, slide the axle shafts back in.
Mark one point on the hub flange with chalk or paint.
Hold the opposite hub flange firmly in place.
Turn the drive pinion a number of times until the chalk mark makes ONE FULL TURN.
Divide that number by two and tell us the answer ( This will give you the diff gear ratio). ie: I'm hoping it will take 6.8 turns of the drive pinion to turn the hub flange one full turn.
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