gear ratio ??

[scotts 72]

how do you find out what gear ratio your truck has ?I have a 72 c-10 with a 12 bolt rear end, and I heard that you can jack up one rear wheel and turn it and count the nuber of times the drive shaft turns. Is this right?How many times do you turn the tire?? thanks

[jrdv]

One full rotation of the tire. You can tape a piece of string to the driveshaft, which will make it easier to count the number of rotations.

[79oldj]

The most accurate way is to count the teeth on the ring and pinion then divide the two numbers. The number will come out close enough to the numbers you hear for gear ratios to distinguish wich it is. Example a 4:10 gear comes out to 409 i beleive.

[cobinder]

Or look and see if your diff still has the factory tag on it. But it will only tell what came in it from the factory. However if you use the string method the tag could confirm your results.

[msgross]

the tooth count will be stamped on the edge of the ring gear i.e 11:41 then divide them = 3.73 rounded up...

yep, you need to take the cover off and then replace the oil but that's cheap maintenance...

[1969K10]

Originally Posted by scotts 72

how do you find out what gear ratio your truck has ?I have a 72 c-10 with a 12 bolt rear end, and I heard that you can jack up one rear wheel and turn it and count the nuber of times the drive shaft turns. Is this right?How many times do you turn the tire?? thanks

If you have an open differential you can do this. When you hear people talk about 373's or 410's, that is 3.73 (or 4.10) turns of the drive shaft per 1 turn of the tire.
If you have a locker or limited slip, you will have to jack up both tires.