please explain gear ratios to me and others that might be afraid to ask
got this off the wikipedia................

A518
The A518, later 46RH (hydraulic controlled governor pressure) and 46RE (electronic controlled governor pressure), is an A727 derivative with overdrive. Starting in the early 1990s, it was used in trucks and vans. The overdrive fourth gear ratio is 0.69:1.
Gear ratios:

1st gear---2.45
2nd gear---1.45
3rd gear---1.00
4th gear---0.69
reverse---2.21

 

is this the kind of explanation you were looking for?

in 3rd gear, the 1:1 ratio means that every 1 turn of the engine yields 1 turn of the transmission output. this gear ratio mean no gear reduction, no gear up. so 2000 rpm's of engine = 2000 turns of the output shaft, which means that you are traveling about 55 mph or so.

in 1st gear, 2.45 engine revolutions yields 1 turn of the output shaft. this is gear reduction.
in 2nd , 1.45 engine revs yields 1 turn.
in 4th, each .69 engine revs yields 1 turn. this is overdrive, or gear up.

suppose you want to travel at 10 mph. with no gear reduction, you'd have to limit you engine rpm to about 300-400 rpm. unfortunately, you engine cannot run at that slow speed, much less produce power. so gearing is used to modify the output rpm to be lower (2.45) or higher (.69) than a straight shaft.

suppose you want to travel at 120 mph. with no gear up, you'd have to run the engine at 5000 rpm or so (which is too fast). with a .69 overdrive gear up, you can run the engine at 4000.

in general, gearing is used to compensate for the limited rpm range of the engine (600-4500) and produce a speed range of 0-100+.

in addition to the transmission gearing, you also have rear end axle gearing of 3.55 or 4.10. this further reduces the transmission gearing to achieve a balance in torque and speed.

 

so............

lets look at first gear

2.45 turns of the engine turns the tranny 1 turn. with a 3.55 rear end that means that every 3.55 turns of the tranny turns the rear end 1 turn?

 

That is indeed how it works.