RPO codes

[linksvu]

I am trying to track down the RPO codes for my '88 Jimmy. Specifically, I tracking down if I have the 28 or 30 splines and whether or not it came with the limited-slip as I am thinking of getting lockrights both up front and our back. Any help would be great guys, thanks.

 

[dyeager535]

G80 is the gov-lock RPO (not limited slip, it will say locking differential IIRC) and the 28-30 spline was not an option, that was a year difference. You can search the forum for the year breakdown, I'm thinking '88 for some reason. I'm sure that the 28/30 spline difference is also somewhat arbitrary right when they started to use the 30's, some early of that year were probably still 28.

 

[linksvu]

The change year is 1988, that is why I am trying to find out if the RPO codes will tell me which one I have as my production date was middle of the year. I knew the G80 was the gov-lock as my Suburban has that however, I am not sure what the LSD code is. Another good thing to know before I order the lockrights as they are different for whichever housing I have. Thank you...

 

[dyeager535]

G80 is the same code for all of GM's LS diff's, even the gov-lock. Cars, trucks, I believe there is only one other LS diff RPO, G79 or something, that was used with RWD/4WD vehicles, but I've never seen it on any 1/2-1 ton truck.

Gov-lock is about all you see in the trucks with G80, although the service manual shows about 4 other diffsthat COULD be in there.

IMO you need to open them up and look, as they could have been changed anyways, or could be shot. Not only do you need to know the spline count, but you need to know what diff is in there. IF working right they can be somewhat discerned by spinning the wheels, but an eaton or auburn LS diff (for instance) would work the same way, but are quite different.

 

[linksvu]

Well, that should work, I might as well do it. I just had the diff fluids changed but oh well, I need to find these things out....

No other way of find the spline count you can think of?

 

[dyeager535]

Nope. If someone swapped a 1987 diff in there, I can't think of any other way to know.

Well, there IS a code that is stamped into the passenger side rear axle tube about halfway out (or supposed to be) but the codes changed EVERY year, (so the same code meaning 2.73 locking one year in a K5 could be a 3.73 open the next) and could be the same between cars and trucks, so unless you have those year specific codes, and know the exact year of the axles, they are pretty much worthless. Again, all it takes is for someone to swap them from stock and you could be screwed buying parts based on what SHOULD be in there.