[Rapdron]

I just received the PHS via email for my 66 Catalina 421 4 speed.
It has box 73-1 checked indicating it has a Safe-T-Track rear axle, but where does it designate what ratio it came with. I think all 421 4 speed cars came with a 3.42, but I would like to know for sure what it is.
I tried looking for the code on the right side axle housing, but too much rust & scale to make anything out.

[61-63]

Get two floor jacks and raise the rear end up where both tires are off the ground, Turn one tire one revolution doesn't matter which tire. Count the revolutions of the yoke on the pumpkin and do the math.

[Stuart]

3.42 would have been the standard offering, but of course there were a couple other ratios that were optional. I was never able to figure out the ratio from the PHS documents, the easiest thing is to do what 61-63 suggests. A chalk mark or a piece of tape on the driveshaft yoke will make it easier to keep track of how many revolutions are made.

[61-63]

Actually there is no math to do here; my bad. If the yoke looks like it turns about 3 1/4 turns as you rotate the tire one revolution you've got a 3.23. Almost 3 1/2 turns and it's a 3.42. Slightly over 3 1/2 turns a 3.64. Etc., etc.

[Yellow Banana]

I’ve found it becomes very clear if instead of a single rotation of the wheel, you turn it 3 or 4 complete revolutions and then do the math. Sometimes those 1/4 turns of the driveshaft can be a little tricky to discern.

[joegpho]

Note that a car with trailer tow - at least the Class III HD package - got 3.73:1 if ordered with 421 HO and manual transmission. I always though my dad's car came with 3.42s but when the car was being put back on the road (2016) the very low mile original gearset was put back in - the surprise was the gear set was 3.73 and not 3.42! I think my dad would like the 2.93s put back in - but I don't agree!