I just finished digging my way to my differential gear ratio on my '75 LT axle. Published specs show this should be 2.73:1, the axle reads PA 2.75:1 (even though I'm reading this sideways I swear it's 2.75). Did the line get creative with either their stamping tools or parts or has my rear been replaced?

Where is the other info: Plant, Date, etc.

Thanks,

KDL

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Red '75 LT
If I only knew more....:)

PA stands for 2.73 no posi

I know this is a limited slip differential. Why is it stammed 2.75:1 instead of 2.73:1?

How bout the other info.(date, place, etc.), where do I find that?

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Red '75 LT
If I only knew more....:)

PU would be a '75 posi 2.73. are you sure its not just rusted and youre seeing the 3 as a 5?

if youre positive its a posi rear end then someone probably swapped it along the way.

NoneToPass,

Are you sure it is a limited slip? Jack up the Rear, put the car in neutral. Turn either side tire forward. If the other one moves the same way it is a posi, if it doesn't it is not a posi.

Sometimes things are not what they appear to be.

Bob R

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1973 Z28 Original Owner
Full Restoration
Yes I am that old.
#'s match

This is getting out of hand. I do not think this is a posi rear, I know it's not cause 1) the stamp says so (PA) and 2) both wheels don't turn together.

My question was (is):

1) What do ya'll make of the stamp being 2.75:1 instead of 2.73:1 (forget PA vs PU)?

2) Where can I find the other info: date code, location, etc.?

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Red '75 LT
If I only knew more....:)

as far as i know the ratio was never stamped on the axel, and i have never heard of a chevy 2.75:1.
Oh, and posi is limited slip...

exactly. limited slip = posi, hence posi rear ends having a limited slip tag. they dont stamp the ratio on the housing AFAIK. every one ive ever seen has just the code.

Well now don't I look the ignorant FOOL. http://www.nastyz28.com/ubb/frown.gif I didn't know posi and limited slip were the same thing. K, I learned my 1 thing fer the day so I can start drinking now http://www.nastyz28.com/ubb/smile.gif http://www.nastyz28.com/ubb/smile.gif

Well maybe someone could educate me on rear types and their differences. I DO know what the ratio means. http://www.nastyz28.com/ubb/wink.gif

Still don't know where to find the production information. I did know where to look for the ratio thanks to Mad Mike's web site at http://www.nastyz28.com/decode.html#axle

Thanks Mike.


KDL

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Red '75 LT
If I only knew more....:)

Chev makes 2 different types. Theres posi, and open...
Open, when you spin one wheel, the other wheel will spin the other way. Posi, when you spin one wheel, the other will spin the same way. There are a couple different types of posi, but i dont know much about them.
Oh, and chill. Every one of us were ignorant fools at one time or other... I still am http://www.nastyz28.com/ubb/smile.gif

[This message has been edited by shawn81z (edited 02-16-2000).]

speak for yourself shawn http://www.nastyz28.com/ubb/smile.gif

i would assume either this was a weird factory occurrence(drunk line worker playing with the punches) or maybe a replacement occurrence(drunk dealer worker playing with the punches).

out of curiosity, how clean(rusty, heavily undercoated, etc...) is the axle tube. ive had some where i couldnt make out the letters to ever see what code i could look up.

Ya ya ya http://www.nastyz28.com/ubb/smile.gif
drunk patgizz is pounding on the keyboard http://www.nastyz28.com/ubb/smile.gif
eheh couldnt resist, sorry http://www.nastyz28.com/ubb/biggrin.gif

Well gents,

The axle was dirty enough that I couldn't read it (or even see a trace of it) without a cleaning. It looks as if they had poured some molten metal (lead?) on their punch location to make it easier to punch. A pretty quick sanding with rough sand paper revieled both the punch marks and the add-on metal pattern for the stamp (you can see how it ran!). The rest of the rear is either completely covered in grease (differential) or medium rust and peeling undercoating (axle tubes).

It may have been sloppy stamping at the factory, grabbed a 5 instead of a 3 by mistake (look TWICE, punch ONCE). Did GM ever make a 2.75:1 rear?

Where is the other build info: date, location, etc.???

Thanks,
KDL

The axle date code etc. are the numbers you have found.

The 1st two digits (PA) is a 2.73:1 open diff used in 1975. PU would be for a posi 2.73:1.

The next digit (another letter) would be the plant code.

The next 3 digits (275) is the build date. Yours being the 275th day of 1975.

The last digit (1) indicates first shift.

Hope this helps, after all, you asked this question a total of 5 times on this post & I figured that you might want an answer.

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70 & 1/2 RS Camaro
406 & M20 4spd
9" rear

70 Malibu
SB350 & TH400

Driveline Technician

WWWWwwwwwhhhhhhooooooo Scooter!!!!!

That explains alot. I thought the 275 1 of PA 275 1 was the ratio! So, since there's no second letter field the plant code ain't there? I'll look again when I get it up on stands. Also, can the 275 stand for the 275th day in 1974 (the car was purchased new in 11/14/74)?

My next attempt at this was going to be a digital picture posting. http://www.nastyz28.com/ubb/smile.gif

Thanks Scooter,
KDL

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Red '75 LT
If I only knew more....:)

DOH!!!!!!

275th day of 1974 is correct!!!!

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70 & 1/2 RS Camaro
406 & M20 4spd
9" rear

70 Malibu
SB350 & TH400

Driveline Technician