well on the 84 Z28 that i just picked up a few weeks back im very confused about the rear end in it.

The RPO codes for the rear are GU5 and Y06

3.23 gears
9.5" saginaw

Correct me if im wrong but isnt the 9.5" a 14 bolt 33 spline rear?

I have never heard of a 14 bolt from the factory...

 

My truck has a 14 bolt 9.5" ring gear but it's a truck diff and was never offered in any car.

GU5 = 3.23 gears

Yes Y06 means a 9.5" ring gear but your car does not have that. You have a 7.5" ring gear 10 bolt diff.

 

Thats what i thought but why the heck would they put a RPO code for a 9.5" when its only the 7.5" ?

 

Don't believe everything on the rpo decal. Anything could have been changed although I have no idea why a third gen would have a Y06 code unless it's actually something else and just looks like Y06 or for some reason third gen's have a different meaning for Y06.

When in doubt, look at the actual part to see what's on the car. The axle code is at the front of the passenger side tube near the center. Some cleaner and a wire brush can pull the code out eventually but even then that doesn't mean someone else hasn't changed what's inside the diff.

My car originally had a 3.27 gear 9 bolt. The only codes listed in the glove box that were related to the diff are:

GW6 = 3.27 gears
G80 = posi

No other codes were specific to the diff however the 9 bolt diff probably fell under a group package code such as the IROC package or performance package. My car had no Y0x codes at all.

 

I should phone them up and raise hell because my RPO sticker says i have a 14 bolt truck rear in my car

 

lol

yeah the 9.5" was the semi floater 14 bolt in 81-up trucks

some 6 lug and most 8 lug

well GM was good with re-using RPO codes sometimes

its no wonder

lol

3.23 is the little baby 7.5" axle of course



good luck