I want to know what rear ratio I have since I got the car recently, and I've been told to prop the rear up, put it in neutral, turn the rear wheel around once and count the driveshaft revolutions. This makes sense to me, but when I did it, I came up with like one and a half driveshaft rev's. I know I'm doing something wrong. The stock tag is still on the diff, but the guy I bought it from says its different, I just want to know what it is. Do I need to have someone turn BOTH back wheels while I count the shaft turns or what? BTW, I'm NOT pulling the diff apart just to count the teeth - I dont care that much lol. So what should I do? Thanks.

 

Take the cover off and look. It's the only sure, accurate way.

Have you changed the fluid since you bought it? Then it needs it. While you're catching up on the overdue maintenance, make a point of looking at the gears, either read the tooth count off of the edge of the ring, or count them yourself.

 

Yeah, like RB said, if you havn't even changed the fluid yet then you need to anyway (just make sure to add posi additive if it's a limited slip rear), but on the ring gear (the BIG gear), on the side of it will be a number, then a : and another number IE ( 42 : 13 ) If you divide the one number into the other, that will give you your gear ratio, (42 / 13 = 3.23) instead of counting all the teeth on both gears and having u'r lil bro make u lose count 5 times. If you have your build sheet then you can find it from your RPO codes, but that's a whole other story. Just pull the cover and u'll know.

 

There is one way to use presicion-guesswork for get an idea what you have.

Get the rear of the car (both wheels) off the ground and put it in neutral. Then, put a mark on the driveshaft where you can see it. Now, turn the wheels, counting each half turn untill the mark on the driveshaft goes around one time to the same spot it started. Count how many times you turned (and partly turned) the wheels and that is your rear end ratio (approx)

Ex. turn the wheels 3-3/4 turns (3.75) to make driveshaft turn 1 time = 3.73 rear end

Thats how i figured out what My car had untill I found out that the L69 cars ALL had 3.73s, lol.

 

Pull the cover

 

No. That method does not work. Think about it....the gear ratio is the number of pinion turns per ring gear turn. If you have 3.73 gears then you have to turn the driveshaft 3.73 turns to get the tires to go around once. If you turn the driveshaft over once with 3.73's then the wheels will turn less than 1/3 of a turn. If you turn the wheels 3 3/4 turns with 3.73 gears then the driveshaft will turn about 14 rotations. Try it and see.

Count the number of driveshaft rotations it takes to make ONE full turn of BOTH wheels and you have a good estimate. Pulling the diff cover is the best way to get the actual ratio.....especially if you just bought the car, and the gears have been changed, and you don't know if Bubba did the gears in his back yard and just used whatever shims he had laying around.

 

Maybe someone can help me out here... there is a way you can do it by driving.... assuming your gears weren't changed and/or your speedo/tach are accurate.

Get on the highway and go 73mph (I believe) in whatever gear is 1:1 (3rd in 700R4, 4th in T5(6)) and read your tach. If your tach comes out to 3230rpm, then you have a 3.23 rear. If your tach reads 4100rpm, then you have a 4.10 rear. If it reads 2730rpm, then get on the phone with Jeg's and order new gears!

 

Just pull the cover, bonus this way is you have nice clean gear oil this way.

 

pull cover and youll find everything out, look on edge of ring gear as you spin driveshaft or a wheel, may need someone to hold other wheel, the teeth counts are stamped right on edge of ring gear in plain sight also year is too.

then you will also know for sure if you have limited slip or not
and have new fluid too as a bonus
its easy to do, all you need is gasket scraper and new gasket and some seal tack stuff to tack gasket to cover real good, or just use white house caulking like the offroad guys do

good luck