[Bermudagto]

I’m trying to Locate the 2 letter stamp on my axle to verify it’s a 3:55. First letters I’ve found are possibly a PR that are stamped overlapping each other. I’m looking for a XV stamp next to a short date code? Gto 455ho no A/c 4-speed.

[F ROCK]

pop the cover and read the numbers on the ring gear or count the teeth.
I could never find the codes on my Pontiac rears but my chevy rear it is faintly stamped on the front side of the passenger side axle tube.
the only way to know for sure is to open it up.

[Bermudagto]

Ok. Thanks.

['ol Pinion head]

Cking gear dates isnt a sure fire way. Many original 72 12 bolt gear sets aren't stamped with date codes.

Looking at the rear cover view, in the lower RH webbing, in that recess, is there a cast date code?

The assembled factory ID coding should be inboards of the center hsg on the drivers side axle tube facing the back of the car. The XV will be stamped differently than the following assembled date stamp & K (for McKinnon). If needed, can text you examples from several original '70 -72 McKinnon produced 12 bolts to show details. The order of stamped codes changed slightly each year.

[Bermudagto]

Originally Posted by 'ol Pinion head

Cking gear dates isnt a sure fire way. Many original 72 12 bolt gear sets aren't stamped with date codes.

Looking at the rear cover view, in the lower RH webbing, in that recess, is there a cast date code?

The assembled factory ID coding should be inboards of the center hsg on the drivers side axle tube facing the back of the car. The XV will be stamped differently than the following assembled date stamp & K (for McKinnon). If needed, can text you examples from several original '70 -72 McKinnon produced 12 bolts to show details. The order of stamped codes changed slightly each year.

I’ll check today. Thank you

['ol Pinion head]

Looked at pics of your car, the 12 bolt center hsg appears to be an original McKinnon cast center housing. Earlier I mis spoke on the stamped code location, double cked several out in the shop today.

To see the original stamping look on the front side of the passenger side axle tube, aprox 2 1/2" to the inboard side of the passenger side coil spring mount. the stamped code will end about an 1 1/4 -1 1/2" before the axle tube goes into the center housing.

The coding system used on '72 model McKinnon 12 bolts, should read like the following:

XV K xxxx E

the xxxx represents numbers, which equate to the day of assembly.

the E at the very end of the string signifys the Eaton posi unit.

[Held for Ransom]

http://www.forums.maxperformanceinc....d.php?t=637541

Now I can agree with 'oPh.

['ol Pinion head]

Originally Posted by Held for Ransom

http://www.forums.maxperformanceinc....d.php?t=637541

Now I can agree with 'oPh.

First page, first picture in that thread shows the casting date of the center housing of a McKinnon cast 12 bolt down on the lower front lip. Occasionally, that casting date is indecipherable due to the last number being replaced by the impression of what looks like a rivet that held the date tag in the mold. Other times, surface rust has attacked that area on the lower lip & the small date code has been obliterated.

The '68, 69, & 70 McKinnobuses embed 12 bolts also have a different way they were coded than later assembled ones.

[Bermudagto]

Located It! Thanks

[Held for Ransom]

Looks like they changed it to a Julian date style.

['ol Pinion head]

Originally Posted by Held for Ransom

Looks like they changed it to a Julian date style.

yes, for '72 models, McKinnon axle plant had to differ the style of coding from '71 style coding.

[Bob Timmermans]

Just get the rear up off the floor and count how many times it takes to turn the driveshaft before a full turn of the wheel.

[AG]

Same marking convention as my 1972 XT rear.

[F ROCK]

Originally Posted by Bermudagto

I’m trying to Locate the 2 letter stamp on my axle to verify it’s a 3:55. .

In his original post he was asking about Gear ratio, not date code.
The only way to know for sure is to count the teeth or read the codes on the gear.