Question1967 Chevy C10. How do I determine the gear ratio in my differential( 2 wheel drive rear end). Found a tag on one of the cover bolts; it was stamped "4".
AnswerHi Pat,
You can take the cover off and change the oil in it, and look for the numbers stamped on the ring gear.
If you just want to be close, find a nice flat parking lot where you can slide under the truck easily, and also roll the truck by hand.
Park it, and make a mark on a tire, where you can roll the truck foreward, and come back to the same mark, one tire revolution foreward.
You can tape a rod to a fender, or mark the sidewall, say like straight down.
Then tape a piece of string to the driveshaft, and put a mark point there.
Roll the truck foreward exactly one tire rev to the mark, being as accurate as you can.
Then slide under the truck and see how many times the string wrapped around the shaft.
Probably about 3 and 3/4 turns, which would be 3.75 turns of the shaft to one turn of the tires, or 3.73:1
Could be 2.73 turns, or just slightly over 4 turns could be 4.11:1
What you are measuring is the ratio of driveshaft turns to axle turns.
2.73, 3.73, and 4.11 are some common ratios.
I don't know if that old a truck had a RPO tag, which is usually in the glove box, and has a bunch of three digit codes.
You can look them up on google as RPO codes.
Van
