Axle codes

I'm sure this has been posted somewhere, but I'm looking for an axle code decoder. Specifically, my axle code is 1.

2.50?

78 LTD II sports touring package (blue), father original owner
67 Mustang (5.0)
69 Mach 1 428 SCJ Drag Pack

i looked in my 74 manual and it starts at a "2" no #1 shown Confused

JOHN
74 GRAN TORINO S&H CLONE
74 VETTE CUSTOM
90 S10 BLAZER 4X4 LIFTED
77 CELICA CUSTOM
75 V8 MONZA SUPERCHARGED
79 COURIER VERT. SLAMMED
75 VEGA V6 5 SPD
70 CHEV C10 P/U
68 MUSTANG FB CONVERSION

We have tons of info on the site, but not as much for the 77 to 79 cars. If you check this link:

http://forum.grantorinosport.org/detailed-data-and-reference-material-by-model-year_topic17833.html

we have all the info year by year including door data plate. The data plate info isn't there for 77 to 79 but 1976 shows a 2 is an open 2.75:1 diff. The 1978 info shows only a 2.50:1 and a 2.75:1 were the only ratios available.

Vince

1972 Ford GTS Sportsroof - Survivor, One Family car

GTS.org Admin

and if the tag is not present from Day 1 there's a reason, anything can be in there

there's always the old fashioned way ...

trans in Neutral, jack 1 rear tire off the ground

can you turn the tire very easily? if yes it's an open differential

if No it may be a Trac-Loc and you'll need to jack both rear tires off the ground

rotate a tire until the valve stem is at 6:00 (bottom) or 12:00 (top) whichever is your preference

now mark the driveshaft in such a way that you can determine when it has completed 1 full turn,

a simple horizontal line 1/2 way between top & bottom will do

now rotate the tire slowly counting how many rotations the driveshaft makes,

stop the tire after 1 complete rotation

how many rotations did the driveshaft make, and how much of a partial rotation?

did it stop exactly on a complete rotation or is it over or under 1/2? how much?

for a Trac-Loc or other Limited Slip that holds the rear tires together solidly (not totally whipped out) the revolutions you counted are the gear ratio

for open diff's or whipped out LS units with only 1 tire off the ground divide your driveshaft revolutions by 2 to find your ratio

the last remainder of an incomplete revolution is the decimal fraction of the ratio so try to be accurate in estimating the partial revolution

72 GT Ute

I suspect your are correct, that it's likely a 2.50:1 rear gear. Rock's method would work to check the ratio, or if you pull the third member at some point, count the teeth and do the math.

If you have a tag on the diff, post it here and I will see if I can decode it for you.

When you upgrade, don't junk the 2.50 or 2.75 gears. They are no longer available new.

Vince

1972 Ford GTS Sportsroof - Survivor, One Family car

GTS.org Admin

i have an "S" code 400 parts car and the door tag says it has a 3.00 in it ...

JOHN
74 GRAN TORINO S&H CLONE
74 VETTE CUSTOM
90 S10 BLAZER 4X4 LIFTED
77 CELICA CUSTOM
75 V8 MONZA SUPERCHARGED
79 COURIER VERT. SLAMMED
75 VEGA V6 5 SPD
70 CHEV C10 P/U
68 MUSTANG FB CONVERSION

On the later cars (77-79) 2.5 was standard axle for the 400.

Some Brainiac at ford said "Let's give 'em the big engine, a C6, and then add 2.5 gears to take away any semblance of performance"

Apparently a practical joke on their buyers.

Wanna see a 78 T-bird with a 400 really wake up? Swap in a 3.5 chunk.

"What we do in full frontal view, is more honest than your cleaned-up mind."
Randy
1979 T-Bird
2005 F-150 STX RCSB 4.6, 3.55 LSD
How the Heck does a REGULAR CAB SHORTBED weigh over 5200 pounds?

not sure on the later cars but 72-76 had mostly 9" but some had 8"
several ways to tell...... the back of the housing is curved with just 2 dimples it's an 8", if it has an extended area for the ring gear on the back it's a 9"
also looking at the front 3rd member 8" has more of a grid pattern on the reinforcing webbing than the 9"
also if you can remove all the nuts with a socket and extension it's an 8" if 1 or 2 are behind the pinion bearing part of the housing it's a 9" Wink

JOHN
74 GRAN TORINO S&H CLONE
74 VETTE CUSTOM
90 S10 BLAZER 4X4 LIFTED
77 CELICA CUSTOM
75 V8 MONZA SUPERCHARGED
79 COURIER VERT. SLAMMED
75 VEGA V6 5 SPD
70 CHEV C10 P/U
68 MUSTANG FB CONVERSION

that 74 4dr i parted had an 8"

JOHN
74 GRAN TORINO S&H CLONE
74 VETTE CUSTOM
90 S10 BLAZER 4X4 LIFTED
77 CELICA CUSTOM
75 V8 MONZA SUPERCHARGED
79 COURIER VERT. SLAMMED
75 VEGA V6 5 SPD
70 CHEV C10 P/U
68 MUSTANG FB CONVERSION

BadHabit351 wrote:

Did you ever determine your ratio? My calculator says that 70 mph @ 2720 rpm with 26" tall tires and a C-6 (1:1 high gear) says 3.00 rear gear.

2.50 gear = 2260 rpm

2.75 gear = 2490 rpm

3.55 hear = 3210 rpm

Yes--my Marti report revealed an axle code 1 is a 2.50. The axle tag was no longer on my differential.

As part of the complete restoration I will be putting in limited slip 3.25.

78 LTD II sports touring package (blue), father original owner
67 Mustang (5.0)
69 Mach 1 428 SCJ Drag Pack