The Stovebolt Site Forums The Shop Area Engine Shop What gear ratio do I have

Today I jacked one rear wheel off the ground and turned the wheel one full turn, the drive shaft moved a little over 2 revolutions, this doesn't sound right but that's what happened? 41 1/2 ton. Any thoughts here.

4.11 seems probable. How are you seeing the driveshaft spin? doesn't your 1/2 ton have a torque tube?

try spinning the wheel twice or even more like 20 times and then devide by 10. sounds complicated but it isn't. the spider gears are taking up 1/2 the travel. so if you spin the wheel twice, you will get a more accurate picture. 20 times even better.

I have the engine and transmission out so I'm lookng at the universal sticking out of the torque tube. Can you explain why I would divide by 10 if I spun the wheel 20 times. I thought if it was a 4.11 the drive shaft would spin 4.11 times for every turn of the wheel. I may have just showed my ignorance. Dave

Its helpful to think about it the way power is applied. When power is applied to the differential by the engine the differential allows the rear wheels to turn at different speeds. When one wheel can not turn the other turns at twice the gear ratio.

So if your ratio is 4.11 that means the drive shaft turns normally 4.11 times for every time the axle turns, or 2.055 times if one wheel is stopped.

Here I think bigbad misspoke. If you stop one wheel and turn the other ten times, you should count 20.55 turns of the drive shaft. Now divide by half of ten, and you'll get the correct ratio, or 4.11

The more turns the easier it is to get an accurate number, but if you have looked up the probable options you rarely need more than a turn or to to narrow it down the the most likely ones.

Are you saying that if I lift both wheels off the ground and spin the drive shaft the wheels will turn 1 revolution for every 4.11 turns of the driveshaft. But, if I stop one of the wheels I will get one wheel revolution for every 2 plus turns of the driveshaft. I don't get it but will accept it.

If you spin the wheel 20 times the this should simulate both wheels spinning 10 times, but your driveshaft should spin something like 41 times if it is a 4.11 or 45.5 if it is a 4.56 ratio. This simple action eliminates some of the guesswork and error

Thanks, I still don't understand the reason for it but I'm going to study up so I understand it, know of any good reference material? Dave

Unless you have a locking differential you can't count on that. If you have a locking diff that is exactly what would happen.

Because of the way the differential works most approaches to counting revolutions have one tire securely on the ground and require a little math to determine the ratio.

Given how rare lockers are in those early years you really need to have one wheel on the ground and do the math.

A differential will transfer the power to the wheel with the least amount of traction,Both wheels on the ground the power is applied equally to both wheels. Now lift one wheel off the ground ,while leaving the other on the ground all the power is transferd to the wheel in the air.and will turn twice as many times.

So when you turn the wheel,lets say 20 times and count the turns on the pinion shaft,you have to divide by 10(or half as many times as you turned the Wheel) to get the gear ratio.