Originally Posted by 67 chevelle (Post 7288202)

code is stamped on axil tube usually passenger side 3 or 4 inches from housing

Originally Posted by hamjet (Post 7288171)

If its a 68 c-10 6 cyl. 3 speed manual originally, (as long as the rear end is stock) it should be a 3:73 gear ratio unless it had the optional 3:07 or 4:11 which would be on the spid. if you pull the rear cover and rotate the ring gear you will see numbers stamped on the edge of the ring gear like 31:8, (made up numbers) and divide them to give you the ratio.

Originally Posted by BLT gmc (Post 7288199)

The info will be stamped on the edge of th ring gear. It should list the # of pinion teeth and ring gear teeth and build date info. Hammer is correct. If I remember correct mine is 11/41 which I believe is 3.73.
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Originally Posted by 67 chevelle (Post 7288202)

code is stamped on axil tube usually passenger side 3 or 4 inches from housing

Originally Posted by LockDoc (Post 7288265)

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http://67-72chevytrucks.com/vboard/s...d.php?t=578793

Code locations posts #8 & #19....

LockDoc

Originally Posted by mike16 (Post 7288331)

you might b able to count the number of teeth on the ring gear and the pinion gear and devide them

also the ratio might be stamped on the ring gear but it wont be a ratio per se but the actual number of teeth on the ring gear and the number of teeth on the pinion gear.

or you could count the number of rotations of your drive shaft to make one wheel rotate 360 degrees.

Originally Posted by Taibo (Post 7288351)

What does that housing stamp tell you about a 48 year old diff that has been through who knows how many owners?

It takes a bit longer to drop the cover but it's the only way to be sure what you have. 37/9 = 4.11!

Originally Posted by hamjet (Post 7288474)

<<<Tried the tire rotation & drive line trick but always came up with only 2 & a 1/3 drive shaft rotations, this trick didn't work for me. Maybe mine is 2 to 1 gears now that's freeway gears, just need a real stout BB to pull it up the hills I need to clime all the time>>> This method usually doesn't work with open rear end only with posi...

Originally Posted by hamjet (Post 7288474)

This method usually doesn't work with open rear end only with posi...

Originally Posted by LockDoc (Post 7288605)

It will work with an open but you only jack up one wheel, not the whole rear end.
LockDoc

Originally Posted by mjgord51 (Post 7288615)

The drive wheel (pass) or drivers side?

Originally Posted by LockDoc (Post 7288605)

It will work with an open but you only jack up one wheel, not the whole rear end.
LockDoc

Originally Posted by Stocker (Post 7288635)

Either side -- as long as one tire is up & the other is on the ground, you're good to go.

Originally Posted by LockDoc (Post 7288605)

It will work with an open but you only jack up one wheel, not the whole rear end.
LockDoc

Originally Posted by Stocker (Post 7288635)

Either side -- as long as one tire is up & the other is on the ground, you're good to go.

Originally Posted by BLT gmc (Post 7295054)

Because your center section is open or non- posi, you will need to rotate the tire two complete rotations while counting the number and fractions of rotation of the driveshaft to find the approximate ratio . In an open diff, when you hold one wheel solid the action of the spider gears will cause the non-solid wheel to travel at an increased rate. This is not the case in a locked diff or a properly functioning posi. In a posi you rotate the tires one revolution while counting the driveshaft rotations. This will give the ratio directly. Bruce
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Originally Posted by Stocker (Post 7295110)

^^ What he said.... rotate the tire two times and count the approx. rotations of the driveshaft.
I was not told the tire needed to go around twice, Thanks.

This link says the same thing, with a bit more detail: http://www.how-to-build-hotrods.com/gear-ratio.html

"If your car has an open rear, jack up only one rear tire and leave the other on the ground. Now put a jackstand under the lifted side. Turn the tire and again count the number of turns of the driveshaft, but this time you must turn the tire two full rotations.

So:

Posi: Jack both wheels off the ground. Turn one wheel 1 complete turn.

- Count the turns on the drive shaft.

Non-posi: Jack one wheel off the ground. Turn the wheel 2 complete turns.

- Count the turns on the drive shaft.

If it takes about 2 and three-quarters turns, it's around a 2.73 gear ratio. If it's a little more than 3, you have 3.08s. If it takes about 3 and a quarter turns of the driveshaft, you have 3.23 or 3.25 gears. Very close to 3 and three-quarter turns, 3.70 or 3.73 gears. This method won't work very well on a posi that's worn-out and won't spin both tires equally.

This method is very handy when looking through junkyards or swap meets. It's good to be able to figure what gear ratio you have without tearing anything apart.

This is a quick and easy way to tell what gear ratio is in your rearend. You might not be able to tell exactly what gear you have, but you'll be very close.

If you want to be accurate, then count the teeth."

Originally Posted by BLT gmc (Post 7295158)

This is a bit of key info and why Stocker and I mentioned it. Keep us posted.
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