Speedometer Gear Question - 727

1.45 is a lot because
275/60-15s are about 28 tall compared to E70-14 being about 24.5 tall. right there we have a difference of 14% and the taller tires are slowing the speed-O down.
but the new 3.73 gear are speeding up the speed-O.
The net effect is therefore actually 45% PLUS 14% = 59%
So with 3.73s you would have to add 59% to the tooth count. That means if the correct gear was in fact 35 teeth, then the current gear would have to be 35/1.59=22 teeth, and therefore the original gear mustabin a 2.34
That's a lot.
Plus I've never heard of a 2.34 Mopar rear gear, in an A-body from the 70s.
I have heard of 2.45s and 2.20s, tho, in FMJ cars from the early 80s
Oh wait that's not right.
Since the 1.45 is absolute, then we have to subtract the 14% from the 45% and get 31% on the gears taking us from 3.73s to 2.57s
So it's still a lot, just not as lot as I thhought,lol.

But you can't do any math until the current gear is out and a tooth-count is on the table. Or you can take a chance that the chart will get you in the ball park and if it isn't, then at least you know what's in there, to order another gear.. In either scenario, you are taking it out twice.
If you jack the back of the car up to get the speed-O adapter up higher than or equal to the bottom of the pan; OR jack the car up by the drivers-side rear corner, THEN
very little oil will come outta there when you pop the adapter out; I've done that many many times.
I got a tip for you tho, start the car up and let it idle for a half a minute to prime the convertor. Sometimes they drain back and an extra qt ends up in the trans-pan.