Hello, pulling rear from the parts car to put into my driver.

I jacked up the rear from the frame and spun the driveshaft by hand and both tires started spinning, first one then the other. I turned one tire but it would spin without spinning the other tire. Turning the driveshaft I think it went 1 and 3/4 turns before the tire went around once. I might have done something wrong here but this just doesnt feel right to me. I did a sand covered asphalt burnout and both tires spun up pretty good under load so Im just confused.

The casting seems to be
NF
X 3917124

I cant find any stamped numbers on this rear. I could never find them on my old 10 bolt either are many just not stamped or maybe I just dont know how to look for one right?


{EDIT}
One more thing, parts car was originally a 4 speed but now has a th400 in it Can I swap driveshaft over from parts car to mine if I have a powerglide now 2004R in near future?

Thanks and please let me know what you all think is going on. Waiting to get a 12 bolt cover seal and the right posi oil would napa have the posi correct stuff?
I will pull the cover and take a picture if that will help once I get whats needed to seal it back up.
Thank you very much.

Both 1968 el caminos, driver is a 307/powerglide/10 bolt open Parts car is a 400 small block th400 12 bolt

Hello, pulling rear from the parts car to put into my driver.

I jacked up the rear from the frame and spun the driveshaft by hand and both tires started spinning, first one then the other. I turned one tire but it would spin without spinning the other tire. Turning the driveshaft I think it went 1 and 3/4 turns before the tire went around once. I might have done something wrong here but this just doesnt feel right to me. I did a sand covered asphalt burnout and both tires spun up pretty good under load so Im just confused.

The casting seems to be
NF
X 3917124

I cant find any stamped numbers on this rear. I could never find them on my old 10 bolt either are many just not stamped or maybe I just dont know how to look for one right?


{EDIT}
One more thing, parts car was originally a 4 speed but now has a th400 in it Can I swap driveshaft over from parts car to mine if I have a powerglide now 2004R in near future?

Thanks and please let me know what you all think is going on. Waiting to get a 12 bolt cover seal and the right posi oil would napa have the posi correct stuff?
I will pull the cover and take a picture if that will help once I get whats needed to seal it back up.
Thank you very much.

Both 1968 el caminos, driver is a 307/powerglide/10 bolt open Parts car is a 400 small block th400 12 bolt

What is your question?

Other than the question about the driveshaft and availability of Posi Rear Lubricant from Napa there apppears to be nothing other than statements of what you did and where the parts came from.

What is your purpose in spinning the rear wheels? Are you trying to determine if you have a posi? Are you trying to determine what the gear ratio is? Do you suspect that there is something wrong with the rearend because one wheel does not immediately spin when you turn the other one?

I am sure you know what you are asking but it is a little bit difficult to determine what you are asking for help with. Try rereading your posts to see if they clearly ask the question you want answered before you submit the post.

it sounds like you have an open rear. also if the other tire didn't spin at all while you turned the one, and the driveshaft turned 1 3/4 times, you just double the 1 3/4 and come up with 3 1/2 or 3.5. the closest ratio to that would be 3.55:1. positraction was standard with 3.73 on up. you are able to get an open with 3.55.
the only way to really tell is to open the cover. the filler plug is shaped differently to hold the posi lube tag. if someone changed it though, you can't be sure. also if the clutches are that worn out that only one wheel turns, also you can't be sure. so pulling the cover and looking at the carrier may be the only way to be positive.
take some pics and post them. plenty of guys here will be able to help you out.

I thought if I spin one tire both should go. Just wanted to see if all that sounds right or if theres something wrong with this rear.

if it is an open rear, then there is no problem. you also won't need posi lube then either.
still to be sure of all this, you should open the rear.
also won't hurt to put fresh oil in it anyway. don't forget the new gasket when you get the oil.

Allen it would be best to pop the cover and check out inside to be sure what you have. The driveshaft spin test you done doesn't sound correct. You can put a piece of tape or chalk mark on the tire and driveshaft and try it again.....Example 3 1/2 revolutions of the driveshaft to 1 revolution on the rear wheel will indicate a 3:55 gear.....If you remove the cover you can just count the teeth on the ring and pinion for verification. It would be best to install some new gear lube/posi additive in a used rear anyway....As far as markings for ID they are normally on the passenger side upper half of the axle tube and could be covered with paint or dirt. With the age of these rear housings the gears could have been changed anytime thru out its life. The driveshaft from the 400 turbo will not work with your glide (length&yoke). I once abused a open 12 bolt open so much the spiders froze I believe and spun posi while on jack stands and on the street.......Good Luck

If you look on the passenger side tube right next to the differential there should be a stamping that identifies what was installed in the axle, where and when and also what kind of posi it came with if it got it. You might need to clean off the area with a brush to see it. Heres a pic with my axle code. turns out I had a posi with 2.73gears. If theres a letter at the end of the stamping that would indicate its a posi. heres a pic

http://i78.photobucket.com/albums/j99/daminature/monteposi008.jpg

http://i78.photobucket.com/albums/j99/daminature/monteposi006.jpg

Thanks folks guess I will do pictures in a couple days when I get out to the field where I store my parts car.

Allen it would be best to pop the cover and check out inside to be sure what you have. The driveshaft spin test you done doesn't sound correct. You can put a piece of tape or chalk mark on the tire and driveshaft and try it again.....Example 3 1/2 revolutions of the driveshaft to 1 revolution on the rear wheel will indicate a 3:55 gear.....If you remove the cover you can just count the teeth on the ring and pinion for verification. It would be best to install some new gear lube/posi additive in a used rear anyway....As far as markings for ID they are normally on the passenger side upper half of the axle tube and could be covered with paint or dirt. With the age of these rear housings the gears could have been changed anytime thru out its life. The driveshaft from the 400 turbo will not work with your glide (length&yoke). I once abused a open 12 bolt open so much the spiders froze I believe and spun posi while on jack stands and on the street.......Good Luckif both wheels are spinning, the you would count the actual revolutions, if only one wheel is spinning, then you double the revolutions of the drive shaft.

if both wheels are spinning, the you would count the actual revolutions, if only one wheel is spinning, then you double the revolutions of the drive shaft.

Tom it doesn't matter if 1 or both spin.......you count the revolutions of the driveshaft to 1 revolution of the tire preferably the passenger side....:thumbsup:

Tom it doesn't matter if 1 or both spin.......you count the revolutions of the driveshaft to 1 revolution of the tire preferably the passenger side....:thumbsup:if you hold the passenger tire from turning, and you turn the drivers side one turn, and the drive shaft turns 1.5 times that would equal a 3:1 ratio. of course if you do the same with the other side, hold the drivers side and turn the passenger side, you will achieve the same result. if you have a posi, both tires will spin, and it is hard to hold one still, so you let both tires spin, but now if you count the rotation of the driveshaft, with both tires spinning the same direction, you see the driveshaft turn 3 times, you still have a 3:1 ratio. the reason the driveshaft turns at a different amount when you hold one wheel is because the differential pinions give you the 2:1 ratio that makes the doubling of the amount of revolutions of the propellar shaft needed. there is no preferred tire to hold still on an open differential, either side will give you the same result.