I was wondering if anyone could help me decode any of these numbers I got off of my rear diff.I got under the car and cleaned all the junk off the rear when I put on my umi lcarcb`s and found these numbers.The rpo codes in my center console tell me it`s g80 which is limited slip if I`m not mistaken and I think gu2 which I believe is 2.73.Just curious what these numders mean.ThanksThe best I could decifer on the passenger side axle tube is 4hdc2882.On the bottom of the diff cover,GMN 22622676.

 

Assuming the cover has never been off in 20 years, it's time to change the oil in the diff. Pull the cover off and count the teeth. If the cover has been off in the past, anything could be inside so the numbers will mean nothing.

 

Stephen87 does make a couple good points.If you haven't changed the axle fluid then there's no telling how long,if ever,since it was changed.And you can either count the number of teeth on the ring and pinion or get the numbers off them.

On the numbers you have off the SPID decal G80 = positraction and GU2 = 2.73 gear ratio.The numbers/letters off the rear axle tube 4HD also indicate the 2.73 ratio with positraction.The C is the plant code(Cleveland I believe)and the 2882 is the build date.When you change the fluid you will need to add the GM positrac fluid additive along with the gear oil.

 

Yeah thats kinda the problem.I just had a bad leak from the pinion seal and it looked like the seal on the diff cover was leaking a little.I took it to the shop I`ve used for years now and asked them to check it out.I asked them to either count the teeth for me or let m e know when thet started the work so I could come look at it myself.Well they did neither.The guy who usually does all my work wasnt there so anyway it didnt get done.They did change the gear oil but said it looked like a peg leg.They replaced the pinion seal and the yoke.Showed me where a groove was cut in one side of the shaft.Said that was weird.I guess it was wobbeling or something.Now seems like my car doesnt spin as easy.Could just be me though.Now I`ve noticed a gear oil type smell after I drove it the first few times.I guess I`m gonna have to pull the rear diff cover again just to find out for sure what it is.Thanks