Greetings and Salutations all....

Ok - 2 questions. I am in the process of upgrading to disc brakes, so I finally got around starting the job. :hurray:

I believe I read here that on one of the gears (large one?) the gear ratio should be stamped somewhere. I have spun that darn thing about twenty times and my finger are close to bleeding and I don't see anything. Where is it? :clonk:

Also, How can I tell if it is posi-traction? The one I have, there is the large gear and 3 or is it 4 smaller gears going around in a circle. :confused:

thanks for your imput.

There is a part number stamped on the outer edge of the ring gear which can be referenced. They didn't actually stamp on the ratio. You can mark a tooth of the ring gear with a crayon and count teeth as it rotates. Do the same for the pinion. Divide pinion tooth count into ring gear tooth count for the ratio.

If you have a posi it will have a metal cage with four springs per side holding clutches inside the differential case (visible through the inspection hole). If all you see are spider gears it is an open rear end (unless it is an aftermarket Auburn rear end which uses two cones, but it will be marked with their name not the GM casting you should have).

I have seen them with the tooth count stamped on the edge of the ring gear, such as 41 10. Divide 10 into 41 and you have a 4.10 ratio. I've also seen them with no stamping at all.

Agree with Dave - sounds like no posi.

And dependent upon gear manufacturer, there is also "37 9" equaling 4.11:1 ratio.

The only # or info I saw stamped was A 45 on the gear that is attached to the driveshaft and on the large one. ( sorry, not good with what each individual gear is called) Thanks for the help.

The only # or info I saw stamped was A 45 on the gear that is attached to the driveshaft and on the large one.Manufacturer's id to keep the two gears as a set. GM did stamp a number and tooth count on the ring gear. ( sorry, not good with what each individual gear is called) Thanks for the help.The gear attached to the driveshaft is called pinion gear. The large gear it meshes with is the ring gear. Those gears at the end of the axle shaft are axle gears. The two gears interfacing with those are the differential pinion gears and they turn about a differential pinion shaft.

The action of the carrier, the case, the ring gear and those gears inside, allow the outside wheel to spin faster than the inner wheel in a turn, hence the name, differential.

http://thumb7.webshots.net/s/thumb3/1/4/61/55410461hkgqKB_th.jpg (http://rides.webshots.com/photo/1055410461041712107hkgqKB)
This is what the 12 bolt Eaton posi looks like. If it has no springs in it then it is probably the standard differential. Some people leave the springs out when they rebuild a Eaton, but that is rare. As for the gears, you probably have after market gears if they have no numbers stmped on the ring gear.

Ok here is why if you have factory gears in the early years GM stamped the or etched the info (part number date code and ratio) on the machined back surface that mounts to the ring gear flange...If you remove the ring gear from your carrier you will see the FACTORY stamping of all the info you need. Now that was really helpful of GM...??? DAH. They did this with the early drop out 8.2 rears and put it on the back machined surface but the ring gear diameter went past the carrier mounting flange and was still visable. But when the 12 bolt came out the flange was a larger diameter for more strength and coved most all of the machined surface making the number NOT visable.

I would say some one at GM realized this after people started to service them and could not quickly reference the ratio and changed it in late 1970 cause 1971 1970 and 1972 they are all on the side edge of the ring gear even some 1969 gears I have seen on the edge of the ring gear too.

There is another way too. If you get at the correct angle and really clean the diff out check the machined flat of the head of the pinion gear, that will also have the part number and date code and ratio stamped/etched into it.

I hope this info help you out. Please you can get this information from J D Race .com anytime Or any other differential question you might have. Take care, Jim - J D Race and Restoration

Jim,

Thanks for the information. My Camaro is a 1970. I have it on Jack stands so it is hard to get a good look in there. I would have to remove the sway bar? in order to get my nugging up there and not end up hanging myself.