Decoding rear differential casting number

[Kateye_Kenzie]

Jumping on this old thread... I'm currently trying to figure out what differential is in this 1974 GMC C6000 truck we're working on so I can get a new differential for it. The VIN is TCE624V556692 and the casting number is 987355. I've talked to just about everyone locally I can find and I'm losing sleep at night over this! If I can get ANY directives from someone who would have half an idea of what might be in this truck I would appreciate it! Thank you!

[BigBird05]

Casting # don't mean much. On the RH axle tube, either on the front or on the bottom will be a stamp letters and numbers. Those will give more info as to year and gear ratio as originally made. Post those and maybe we can help.

[Kateye_Kenzie]

Just spoke with the boss... there are none of those numbers on the axle and that's why he only gave me the casting number... And the pinion is broke out of it and missing so I can't rely on that either. Does anyone know what was in these trucks out of factory? I'm talking to the GM Heritage Center right now but they take weeks to reply...

[C10 - C90 Bill]

Check out the info on the SPID.

[Bob B.]

Yes, check the SPID label, should be in the glove box. Problem is these trucks were available with many rear axles, GM, Eaton, Spicer, ect.. Good news is most medium truck axles were common and used in many makes of trucks, so parts availablilty is usually not a problem.

[Kateye_Kenzie]

Originally Posted by Bob B.

Yes, check the SPID label, should be in the glove box. Problem is these trucks were available with many rear axles, GM, Eaton, Spicer, ect.. Good news is most medium truck axles were common and used in many makes of trucks, so parts availablilty is usually not a problem.

I feel kind of ridiculous asking but what's the SPID label? How would I read something like that? What does it look like? And why have I never heard of it before?

[C10 - C90 Bill]

SPID is short for Service Parts Identification.

It's a label that tells the info on your truck when it was built. I didn't indicate where it would be on a '74, as my knowledge pretty much stops at '72. But like Bob has indicated check the inside of your Glove Box Door. They can be a little hard to decipher, but look for the info for the rear. If necessary, try to post a picture of it. Hopefully it is still there.

[C10 - C90 Bill]

Double post

[Pick121]

Originally Posted by Kateye_Kenzie

Just spoke with the boss... there are none of those numbers on the axle and that's why he only gave me the casting number... And the pinion is broke out of it and missing so I can't rely on that either. Does anyone know what was in these trucks out of factory? I'm talking to the GM Heritage Center right now but they take weeks to reply...

Hello, not to challenge “the Boss” but, the rear axle stamp numbers are different from the casting numbers, are easy to miss if covered in road dirt & grime. They may be on the axle tube itself. Might find them with a closer look, wire brush/degreaser. See attached photo for example. It is possible they might not be on the axle, or unreadable, but if he can find them it will be way easier to determine the rearend

[Kateye_Kenzie]

Originally Posted by Pick121

Hello, not to challenge “the Boss” but, the rear axle stamp numbers are different from the casting numbers, are easy to miss if covered in road dirt & grime. They may be on the axle tube itself. Might find them with a closer look, wire brush/degreaser. See attached photo for example. It is possible they might not be on the axle, or unreadable, but if he can find them it will be way easier to determine the rearend

I've also thought of that and the problem with that method is that..... those numbers are nonexistent! They're nowhere to be found, which is why I'm struggling so darn hard. Thank you, however.