Rear end identification

I posted a possibly incorrect method..took it off. My memory does goofy stuff some times. Google "determine rear gear ratio". Google is your friend.

 

it will be stamped on your input shaft as well---in #--its been awhile,so i cant remember exactely how you figure it out--but you can

 

To get a close estimate take a piece of string and tape it to the drive shaft at one end and let the other hang to the ground. Put a mark on the tire and move the truck till the tire turnes exactly one time. Then count the amount of times the string wraped around the drive shaft. Just over 3.5 you got 3.55s or 3.58s, 3 and 3/4 you got 3.70s or 3.73s. Just under 4. you got 3.90s or 3.91s. just over 4 you got 4.10s and so on.
You could also use the road speed calculator on eaton fullers web site. You just put in your road speed at a certain RPM and your tire size and transmissions top ratio and it will give you a chart with your gear ratio.

 

after much brain farting i remembered---on the pinion shaft there are 2 numbers--divide one into the other and that will be the ratio
dont go by the numbers on the axle housing--in casr the diffs have been changed to a different ratio---and dont ask me about what happens with 2 different diffs

 

The truck might be too old to be in electronic records, but a call to your local Pete dealer should help you with information one way or the other. They will need the VIN of your truck.

 

(_|_) <---

 

I start with sticker. then I use to read parameters from ECM and if speedo reads correct milage there is correct ratio in ECM memory. The next stop - with VIN. and there are ID plates on axes

 

No ECM's on an 83!