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help axle tag ID

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gotfords

help axle tag ID

ok
so i understand the tag means 2.75 with locker...also know the 9 mans 9"
what i want to know is what the
"S315A" means

supposedly oem rear end in 80 f100 with 300 and manual trans but 5x5.5 bolt pattern???
oh and it says locker but when i jacked up rear off the ground I rotated one tire and the other side rotated the opposite?? did not think that was a sign of a locker??? thought if it was a locker both wheels would spin in same direction? or should i have spun drive shaft???? make a difference???
thanks

TOMMY SIDES
KINGMAN AZ

1986 F150 SWB 2WD REG CAB INLINE 6
4BBL CARB OFFY INTAKE SPLIT HEADER LOWERED 3" F AND 4" R

1984 F250 LWB 2WD REG CAB 460 CARB CALIFORNIA TRUCK
IT PASSES SMOG...LOL

1980 f100 REG CAB SHORT BED 2WD...NO MOTOR OR TRANNY YET!!! FACTORY 300 W/MANUAL IN FLOOR AND A/C

Rembrant

Re: help axle tag ID

gotfords wrote

what i want to know is what the
"S315A" means

Assembly plant code I think. I don't think it's a useful number for your purposes. Somebody can correct me if I'm wrong.

1994 F150 4x2 Flareside. 5.0 w/MAF, 4R70W, stock.
1984 F150 4X2 Flareside. Mild 302 w/ 5spd. Sold.
1980 F150 4X4 Flareside. 300i6 w/ 5spd. Sold in 2021.
1980 F100 4X2 Flareside. 351w/2bbl w/NP435. Sold in 1995

gotfords

Re: help axle tag ID

hoping to find exact production date

Rembrant

Re: help axle tag ID

gotfords wrote

hoping to find exact production date

That would be the 9L21. The 9 indicates 1979, the L indicates December, and the 21 is the 21st day of the month.

What is the build date on your 1980?

gotfords

Re: help axle tag ID

it says dec. 1979....close enough i guess...my marti report says built dec. 12th 5 days late actually they say...close enough i guess

gotfords

Re: help axle tag ID

In reply to this post by Rembrant

thanks for the help...kinda weird a 2.75 came with a locker...lol

gotfords

Re: help axle tag ID

also kinda odd they would have been working on dec 21st tooo...it was a friday.....ususally they shut down for Christmas and for inventory for most of the month...

myrl883

Re: help axle tag ID

S315A is the part number for the differential assembly, S indicates it was built at the Sterling axle plant.

9L21 is NOVEMBER 21, 1979...

Ford Parts Monkey since 1985
1981 F100 Flareside - Black, 302-4V Roller/AOD
1986 F150 Flareside - Medium Fire Red 302/AOD
1989 F150 Standard Cab 4x4 - Dk Shadow Blue 302/AOD
1993 F350 4x4 Crew Cab - 7.3 IDI/ZF-5
I think it's a sickness...

gotfords

Re: help axle tag ID

thanks...i see how "L" is Nov. now...makes better sense for my build date of 12/12

Rembrant

Re: help axle tag ID

gotfords wrote

thanks...i see how "L" is Nov. now...makes better sense for my build date of 12/12

That certainly makes more sense. I did see somewhere before the M=December, but how do the months correlate with the letters?...since I got it wrong.

myrl883

Re: help axle tag ID

Yes, months are A-M = January-December. I is not used, because it is too easily confused with 1. This applies to build dates and VIN numbers - I and (letter) O are never used.

Rembrant

Re: help axle tag ID

myrl883 wrote

Yes, months are A-M = January-December. I is not used, because it is too easily confused with 1. This applies to build dates and VIN numbers - I and (letter) O are never used.

I was today years old when I learned this interesting fact. Thank you sir!