ginjam

How do I determine the gear ratio for the rear-end?

gerry72

Easiest way is to decode it from the stamping on the very bottom of the case. You'll have to put the car in the air to do this. Then post the code here and someone will tell you how it left the factory.

While the car is in the air, you can put a chalk mark on the driveshaft and one on a tire. Then have someone turn your driveshaft. You monitor the mark on the tire, they monitor the mark on the shaft. Once the tire makes one revolution, they tell you how many times the driveshaft turned. If they same almost a perfect three turns of the shaft, then it's likely a 3.08. Three and a third, a 3.36 and so on.

SoCalErv

Here is a rule of thumb

Gear Ratio RPM@70 mph
411:1 3800 rpm
370:1 3200 rpm
355:1 3100 rpm
308:1 2500 rpm

You should check the numbers on your differential because no one knows if Bubba has been there.

ford4play

obviously, the most accurate would be to pull rear cover. count teeth on ring gear, count teeth on pinion gear. rear ratio=ring gear/pinion gear. if bubba has been in there, rear codes may not do any good

Gary's 1977 Vette

If you do not want to take off the rearend cover you can get close by turning the wheel one compete turn and counting how many times your drive shaft turns. The drive shaft will turn probably 3 + fraction times. Figure the fraction as a % and you will be real close to your rear end gear. Like 3 and 1/2 turns would be 3.50 to 1 If it turns 3 and 1/4 then it will be 3.25 to 1. This will put you in the ball park without removing the rear cover.

ginjam

Thanks for the help.