3.73 to 3.08

[bigtendude]

Now that I have exhausted my possibilities of getting freebie gear set for my truck, I need to know for sure if 3.08 gear set would fit in my 12 bolt rear end, there is 3.73 in it now. If I buy new set, then I will have it installed by a friend, but I need to know if it would work, my truck originally came with a 3.08, it got burned up from original owner hauling 5th. wheel with it, so he had 3.73 axle assembly installed. I have early 1978 C10 Big 10, 350cui., and TH350 2 wheel drive, I could swear that when I make wheels spin that I leave two cleaned pavement marks, or so I've been told...lol. Is it possible that I have posi? thanks in advance

[Pontiac1976]

Yes it should just buy the right one for the diff in your truck and all the shim's bearing or ( 3.08 gear in stall kit you still might need a few inner parts some time ) there a few company's to look at . You can call them most times on a tech toll free line .

[bigtendude]

I have some numbers from off of the outer part of the pig assembly, no numbers on either axle tube, though. I had posted these numbers somewhere on this site already, it didn't seem like anyone at that time knew anything about these numbers. They are on the right front part of the assembly, towards front of the truck. Close to the center. I saw a site in a link on this one, they want 225.00 for 3.08 gear set. Would I also need a carrier? I think that's what it is called.

[bigtendude]

The website is Jawsgear.com

[Pontiac1976]

well does not look to bad if it's close that would be better.
afew others I would shop around a little plus there any speed shop in your town. summit, jags, just two and they both have tech lines

[bigtendude]

Thanks for the reply, yes there are a couple shops in the area. How much do you think it would cost to have them installed, as I am a little cash strapped? And also, how do I tell if I have posi in there? When I mashed pedal to the metal from standstill, I leave two tracks on pavement....lol. Other than taking cover off of housing? Thanks in advance.

[bigtendude]

Also, will the numbers on the housing tell me anything?

[Pontiac1976]

some of the # will tell you the gear in your diff if it has not been swapped out., some are just caseing # of the diff caes.
here try this : GH2 76 87 AXLE,RR 2.29 RATIO
GH3 86 88 AXLE,RR 2.77 RATIO
GH4 76 81 AXLE,RR 2.28 RATIO
GL1 76 81 DIFFERENTIAL CARRIER,RA AXLE,ALUM
GM1 87 87 AXLE,RR 2.59 RATIO
GM3 85 88 AXLE,RR 3.45 RATIO
GM7 82 83 AXLE.RR 2.39 RATIO
GM8 76 88 AXLE,RR 2.56 RATIO
GN3 76 81 DRIVER CONTROL LEVELING
GQ1 REAR AXLE - STANDARD
GS4 85 86 AXLE,RR 3.70 RATIO
GT4 76 88 AXLE,RR 3.73 RATIO
GT5 76 88 AXLE,RR 4.10 RATIO
GT8 76 88 AXLE,H.D. RR 4.10 RATIO
GU1 76 87 AXLE,RR 2.41 RATIO
GU2 76 88 AXLE,RR 2.73 RATIO
GU3 82 85 AXLE.AR 2.93 RATIO
GU4 76 88 AXLE,RR 3.08 RATIO
GU5 76 88 AXLE,RR 3.23 RATIO
GU6 76 88 AXLE,RR 3.42 RATIO
GV4 82 87 AXLE,RR 3.36 RATIO
GV8 82 85 AXLE,RR 2.72 RATIO
GW4 84 85 AXLE,RR 3.31 RATIO
GW6 85 88 AXLE,RR 3.27 RATIO
GW9 76 88 AXLE,RR 2.93 RATIO
GX3 82 88 AXLE,FRT 3.33 RATIO
GX4 76 83 AXLE,RR 3.75 RATIO
GX5 76 83 AXLE,RR 4.09 RATIO
GY5 76 87 AXLE,FRT 3.65 RATIO
G44 85 87 AXLE,RR 3.07 RATIO
G50 76 88 SPRING,H.D. RR(VAR 1)
G51 76 87 SPRING,SPL H.D. RR(VAR 2)
G52 82 87 SPRING,EXTRA CAPACITY RR
G60 76 88 SPRING,AUX
G66 76 88 ABSORBER,AIR BOOSTER RR SHK
G67 76 77 ABSORBER,AUTO LVL CONT SHK SYS
G67 78 88 ABSORBER,ELEC LVL CONT SHK SYS
G72 80 80 AXLE,RR 2.14 RATIO
G72 81 81 AXLE,RR 2.14 RATIO (EXPORT)
G72 82 87 AXLE,RR 2.14 RATIO
G75 82 87 AXLE,RR 3.62 RATIO
G80 76 88 AXLE,RR LOCKING TYPE
G83 82 83 GEAR,RING 8.75 IN
G87 76 87 GEAR,RING 8.50 IN
G88 76 83 GEAR,RING 8,875 IN
G89 76 87 GEAR,RING 7.50 IN
G92 76 88 AXLE,PERFORMANCE RATIO
G95 85 88 AXLE,ECONOMY RATIO
HA3 82 88 AXLE,RR 5.29 RATIO
HC2 76 81 AXLE,RR 2.76 RATIO
HC4 76 88 AXLE,RR 4.56 RATIO
HC7 76 88 AXLE,RR 5.13 RATIO
HC8 76 87 AXLE,RR 3.21 RATIO
HD1 82 84 AXLE,RR 5.83 RATIO
HE3 76 84 AXLE,RR 3.07 RATIO
HE4 76 81 AXLE,RR 3.40 RATIO
HF7 76 88 AXLE,H.D. RR 4.56 RATIO
HF8 76 88 AXLE,RR 4.88 RATIO
HK1 82 86 AXLE,RR 2.87 RATIO
HK9 82 84 AXLE,RR 5.86 RATIO
H04 76 87 AXLE,RR 4.11 RATIO
H22 76 81 AXLE,RR 6.17 RATIO
H23 76 81 AXLE,RR 5.43 RATIO

[Pontiac1976]

your may be listed or not but it will give you idea.

Assembly Plant Codes Plant Code Plant Code
Buick B Warren, MI W
Buffalo C Oldsmobile O
Cadillac D Pontiac P
Detriot Gear & Axle G Pontiac/Canada M
GM of Canada K

Shift: D or 1 = Day shift | N or 2 = Night shift
Positraction Source/Code:
- = No positraction G = Chevrolet G&A Positraction Carrier
D = Dana Positraction Differential O = Oldsmobile Positraction Carrier
E = Eaton Positraction Differential W = Warren/Warner Motive

Positraction Casting Numbers
Due to the possible confusion with gear ratio descriptions... a HIGHER number is a LOWER gear.
In the below examples, 2.73:1 & down = 2.41, 2.56, etc... which is actually a HIGHER gear ratio.


8.2" 10 bolt 8.5" "Corporate" 12 bolt
Casting # Series Gearing
ED32118 2 2.73:1 & down
EDB30116 3 3.08:1 & up
Casting # Series Gearing
410408N 3 2.73:1 & up
410409N 2 2.56:1 & down
Casting # Series Gearing
ED32088 2 2.73:1 & down
30140PM1 3 3.08:1 to 3.73:1
EDB30174 4 3.90:1 & up

this shows on the center part of the diff. printed on flat spot edge

Rear Housing Casting Date
Example: D141 - (D = Month, 14 = Day, 1 = Last digit of year (1971)).

Month: A = Jan, B = Feb, C = Mar, D = Apr, E = May, F = Jun G = July, H = Aug, I = Sep, J = Oct, K = Nov, L = Dec






Ring & Pinion Gears
Axle Ratio Tooth Combination
2.56:1 41,16
2.73:1 41,15
3.07:1 43,14
3.08:1 40,13
3.08:1 37,12
3.31:1 43,13
3.36:1 37,11
3.42:1 41,12
3.55:1 39,11
3.73:1 41,11
4.10:1 41,10
4.11:1 37,9

[bigtendude]

OK here is what I finally found on right side of axle tube.. A D K M 0 0 6 1