I think some of this has to do with the converter. My belvedere has 3:23 (I put them in there). 255/60's and an old Banana converter and it is also 2800 at 60mph.

That could be. It's pretty quick for a go kart motor!

Might be 3.23 or it could be 3.55. there's slip in the converter so it's engine is always going to turn higher than a 1:1 to the tail shaft like a clutch car.

I don't recall a 3.73 being offered, maybe it's a 3.91 though.

It never was an offered ratio by Chrysler back in the day . I don't think it's 3.91 , My dart has that gear with a 26" tire , 4 speed and it buzzes higher than that .

The easiest way to find out quickly what ratio you have without removing the third member is to jack the car up on jackstands so you can crawl under it and mark the driveshaft rear pinion yoke and the third member so you can count the drive shaft revolutions when rotating one of the rear tires one revolution If it has a posi unit or spool, and the drive shaft rotates 2 3/4 turns it has 2:76 gears, if it rotates almost 3 complete revolutions it has 2.92 gears, 3 1/4 revolutions 3.23 and so on
If it has a non posi rear end you need to lock up one tire so it won't move and then rotate the other tire two complete revolutions of the other tire and count the driveshaft revolutions to get it correct due to the spide(corrected )r gears having to do their thing properly on rotating with the driveshaft with the other wheel being held
Thanks for pointing out my bad spelling

You sir are wrong on this
I bought a 1960 Dodge Phoenix in 1967 that had that ratio in it stock, saw the same ratio in a 1957 Plymouth Savoy six cylinder stick shift later also, both cars had not been messed with back then, they were stock

Fixedf it for ya

I think he was thinking 62 and up

the small diameter borescope cameras are so good and inexpensive that
counting the teeth of the pinion and ring gear may involve the least sweat and effort
- plus an unexpected problem might be spotted early

I would have never guessed that “prime numbers” of gear teeth are much preferred for better durability and lower whine noise.

I knew some old fart was going to come in and say that , I should have said ... that ratio was not offered in 1969 in passenger cars .... better ???

More like the muscle car era and in passenger cars ... but yes post 62 , I should have been clearer

That's OK John, we all make statements that can be taken out of context. BTW, I fixed his "SPEEDER" gears a couple of comments earlier

to both for your contributions to the "BORED"

Why would anybody even guess with calculations etc. I do not get it. Jack car up, count drive shaft revolutions compared to tire revolutions. Done. MPH vs RPM vs Tire size........ Really. It amazes me how many people do a gear change but do not change trans speedo gear. That could be way off. What happened to keep it simple?

You must be new to the internet ?...

I may be alone in this aspect, but 3.73 is a rather rare ratio in the first place.