The Stovebolt Site Forums The Shop Area Engine Shop rear end identification #'s

I was given this rear but I don't know anything about it. The #'s I found are GM 30 and 125433. Can anyone give me info or tell me where to find it? Thanks

You are going to have to look inside for gear ratio number. I think you are looking at casting or mold numbers. Look on the ring gear for numbers and a date code. Or just count the teeth of each gear. Joe

1st Time53: Joe H has given you good advice on finding out the ratio of your rear end. Some times the numbers stamped on the ring gear are illegible. What you do then is drain the oil, take the rear cover off, look on the outside edge of the largest gear (ring gear)for the ratio stamped there. If you can't find or read it then take a marking pen or make a mark somehow in the large ring gear and count the teeth. Now look forward into the differential and you will see the pinion gear. Its the one that drives the large ring gear. Mark it on the back side of one of the teeth and count the teeth on that. For most older pickups you will find 10 teeth on the pinion and 39 on the ring making the ratio 39.10 or 3.9:1. Yours may have a different number of teeth.

More ways to identify the make and year of the rear end:
1. Is it a closed torque tube type or open type where you can see the U-joint yoke on the front of the rear end.
2. Is it set up for leaf springs or coil? If leaf spring how far apart are the spring perchs?
3. How many wheel mounting studs on the flange at the end of the axle? Most likely 6 but could be 5.
4. What is the shape of the rear cover? round or some other shape?
5. If the backing plate is still on the end of the axle housing and the wheel cylinders are on it they should have a number cast or stamped in them. If you take that number and go to something like the NAPA on line site and go to the brake area and type in the wheel cyl # it may identify it for you or the counterman at most auto parts stores might be able to look it up and you could infer the year and make of the vehicle the rear end came from. Not full proof but a very strong clue.
6. How many studs/bolts hold the rear cover on?
7. If you have a digital camera and can post pics of the rear end somewhere and provide a link to those pics that would be very helpful as some of the guys here are so good they can just look at it and tell you what it is. Don't send or attach a pic to a post on the forum. Its apparently a no-no as it takes up too much space.
7A If you don't have a place for posting pics go to Yahoo and get an album free and post your rear end pics there in an album and then make the album available for public viewing and send an invite to view along with the next post to this forum after you have checked to see that indeed you can get in to look at your album.
7B Take a fairly close up pic of the back cover, ea. side and the front and a full width pic showing the whole rear end including axle housings and a pic showing the axle ends with wheel mounting studs.
Hope this is helpful.
Jerry
I understand your frustration at not being able to identify the rear end but I just went through a similar thing to identify a first series 10 bolt rear end that turned out to be out of a 58 Chevy 1/2 ton.