OK....Just am finguring this out today when I replaced my axle seals and bearings:

I have a 1991 camaro Convertible Z28 that should have:
28 spline axles
2.73 rear
posi rear

This is what I found:

Axle tube (1st 3 letters): 6HT which should be a 88 or 89 with a 2.73 posi

This is what I found:
26 spline axles
3.42
0pen rear

And too make it more confusing, on the top of the carrier above where the gear oil drain plug is I have a little plastic fitting that I can pull out reavealing a little port in the top. I have no idea what the little plastic port is for. I almost think it might be an ABS sensor port.......

What the hell???

 

That little plastic "top hat" on mine is the breather hole.

 

Sounds to me like your car's rear has been swapped out at some time or other.

Pretty common actually.

No point in getting all worked up over how it "should" have this or that. The car has what it has now. Period. Buy stuff that fits it now that you know what it is.

This is why all of that "codes" BS is just that.... BS. People change stuff out. NEVER EVER buy parts for something like that, until you place your eyeball upon the parts in question and verify what they are. Especially when you know perfectly well, as you obviously do, that there's a possibility for variation.

 

Yeah....I was just freaked out yesterday. I'd been under the car all day in the rain....replacing bearings/seals when I noticed I lost a side gear shim in the diff. I just wanted to get the correct parts and finish.....

Actually I think its cool that I have 3.42 rear. Good to know when I buy a posi unit for a 3-series carrier.

 

I gotta agree!!

That's a WHOLE LOT BETTER than your "codes" telling you it's 3.42, but finding 2.73s.

Sux that it's 26-spline instead of 28 though. Oh well.

 

haha someone lucked out! BTW, have any pics of your car? I'm a sucker for the 'verts