3/4 Ton rear end question

[koolky]

I have a 1968 C20 and a 1970 C20 Longhorn with the eaton rear ends in them. I think they both have 4.57 gears, My question is if my trucks dont have an option that says 'posi' or 'no-spin', do they have posi's in them or was that option only???

[uncle]

Option,unless someone changed it through the years.

[72armyswbtruck]

Exactly as UNCLE said,
? Do you know how to check if it is posi rear end or not?

[koolky]

jack it up, turn one wheel, if the other turns the same way, its a posi?

[factorystock]

Unless you physically spin the wheel and count the drive shaft rotations it is difficult to determine the axle ratio on C 20 trucks sight unseen. The SPID,(glove box decal) usually is not helpful. In 1968 the sales brochure lists 4.57 (eaton) standard, with 4.11 (eaton) and 3.54 (dana)as options. In a 1970 sales brochure, it list 4.57(eaton) as standard, and 4.10 (dana) 3.54 (dana) 4.56 (dana) as options. The 4.11 and 4.57 is a eaton axle and the 4.10 and 4.56 are dana axles.So the question is did they make a 4.11 eaton after 1968? There is a 69 c-20 being parted out in a local wrecking yard with a eaton rear end and coil springs and the SPID decal has no mention of the ratio but it has a LS9 350 option and a M49 turbo hydramatic option.When sitting on its wheels, it is a little fustrating trying to figure out the ratio. Iam assuming it is a 4.57, according to sales brochures, since there is no listing of a 4.11 ratio in C 20 series in 1969.

[Longhorn Man]

All small blocks with autos were 4.10 unless optioned otherwise in the C/20 series. My observations (and dealer books confirm) have indicated this across the board 67 - 72

[Green Machine]

I used to have a 71 Custom Camper C20 350/350 - it had 4.56(7) Eaton rear, but it had the tall split rim tires too. Our current 71 C20 has the 4.10 eaton,this one has (had) the 16.5 wheels.

[special-K]

Pull the covers off and both questions will be answered,positively.
I don`t think the sales brochures got into the nitty-gritty on gearing options.At least,not the differences between the Dana and Corporate rears,since they are virtually the same ratios(except the 3.54 Dana).That was more a matter of coil or leaf rear suspension preference.

[kris's66lwb]

what # would be on the ring gear on a 410

[factorystock]

Koolky, Did you figure out your gear ratios on your eaton rear ends yet? Please let us know.

[koolky]

It'll be another week before i can take the cover off and have a look, but acording to my book I got here they should both be 4.57