3/4 Ton rear end question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

koolky · 04-15-2008, 11:13 PM

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** · 04-15-2008, 11:14 PM

Option,unless someone changed it through the years.

72armyswbtruck · 04-16-2008, 03:15 AM

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

koolky · 04-16-2008, 03:16 AM

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

factorystock · 04-16-2008, 04:25 AM

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 · 04-16-2008, 05:20 AM

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** · 04-16-2008, 05:46 AM

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** · 04-16-2008, 01:02 PM

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 · 04-16-2008, 09:05 PM

what # would be on the ring gear on a 410

factorystock · 04-30-2008, 02:32 AM

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

koolky · 04-30-2008, 03:24 AM

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

04-15-2008, 11:13 PM	#1
koolky 67-72 Addicted Join Date: Oct 2007 Location: Guelph Ontario Posts: 256	3/4 Ton rear end question 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???

04-15-2008, 11:14 PM	#2
uncle Senior Member Join Date: Aug 2003 Location: Conyers,Ga. Posts: 7,286	Re: 3/4 Ton rear end question Option,unless someone changed it through the years.

04-16-2008, 03:15 AM	#3
72armyswbtruck Registered User Join Date: Feb 2004 Location: Idaho Posts: 4,034	Re: 3/4 Ton rear end question Exactly as UNCLE said, ? Do you know how to check if it is posi rear end or not? __________________ "Remember, They can Kill You, but they can't eat You, That's against the law!!!!!!!!!"

04-16-2008, 03:16 AM	#4
koolky 67-72 Addicted Join Date: Oct 2007 Location: Guelph Ontario Posts: 256	Re: 3/4 Ton rear end question jack it up, turn one wheel, if the other turns the same way, its a posi?

04-16-2008, 04:25 AM	#5
factorystock Registered User Join Date: Feb 2007 Location: west coast Posts: 3,363	Re: 3/4 Ton rear end question 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.

04-16-2008, 05:20 AM	#6
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: 3/4 Ton rear end question 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

04-16-2008, 05:46 AM	#7
Green Machine Senior Member Join Date: Jul 2004 Location: Estherville, Iowa Posts: 3,371	Re: 3/4 Ton rear end question 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. __________________ 1968 C10 307 3spd Long Fleet ------ http://67-72chevytrucks.com/vboard/s...d.php?t=201103 1970 C10 305 Super T10 Long Fleet --- http://67-72chevytrucks.com/vboard/s...d.php?t=202285 1971 C20 383 TH350 Dana Posi ----- http://67-72chevytrucks.com/vboard/s...d.php?t=206894 2001 GMC Sierra 1500 C3 6.0

04-16-2008, 01:02 PM	#8
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,862	Re: 3/4 Ton rear end question 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. __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

04-16-2008, 09:05 PM	#9
kris's66lwb resident wrencher Join Date: Dec 2006 Location: ramona california Posts: 720	Re: 3/4 Ton rear end question what # would be on the ring gear on a 410

04-30-2008, 02:32 AM	#10
factorystock Registered User Join Date: Feb 2007 Location: west coast Posts: 3,363	Re: 3/4 Ton rear end question Koolky, Did you figure out your gear ratios on your eaton rear ends yet? Please let us know.

04-30-2008, 03:24 AM	#11
koolky 67-72 Addicted Join Date: Oct 2007 Location: Guelph Ontario Posts: 256	Re: 3/4 Ton rear end question 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



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