3.73 for eaton rearend? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

eke82 · 03-27-2008, 01:07 AM

my dad and i have a 72 3/4 4x4 4spd with 4.10 he wants to put 3.73 in it for hiway but i dont thinK 3.73 are available for the eaton rearends but he tought they were

desertPOS · 03-27-2008, 01:09 AM

pretty sure that's what I have in my '69 C20 ho52

stllookn · 03-27-2008, 01:23 AM

3.73 is the ratio in my Dana. Coincidence?

**special-K** · 03-27-2008, 01:25 AM

4.10 was the highest gear GM offered.There were 3.90s made at one time by outside sources.You can get 3.73s for the Dana44 and swap-in a 3.73 14-bolt.`72-earlier GMC trucks could have Dana60s with a higher gear,3.54?,or something like that.Whatever it is,that`s what my`72 Sierra has and it rolls along nicely with 12.50/33s(TH350).But,it gets the same mileage as my`72 Highlander with 4.10s and 12.50/35s(SM465).

mnunn454 · 03-29-2008, 02:54 AM

I ordered and installed 3.73's and a new Eaton posi carrier a few years ago. Parts all easily obtainable.

However, it you're after improved fuel mileage in a 4X4, dropping the ratio by 10% (4.11 down to 3.73 is about 10%) will net you a little savings, but not nearly enough (IMO) to pay for the gear swap costs.

Said another way, if you spend $200 a month now in fuel and can reduce that by 10% with a gear swap, it'll take about 30 months (2.5 years) of driving before you've paid back the upgrade cost and start "saving" any money.

Food for thought...

**special-K** · 03-29-2008, 03:53 AM

Where did you find 3.73s for a Corporate rear?I`d like to talk to them.

Longhorn Man · 03-29-2008, 05:16 AM

I think he installed an eaton built assembly in his 1/2 ton 12 bolt. If you look at his siggy, he has a C/10.
We are talking about the corperate rear/eaton diff rear that came stock in the C/20 & 30trucks.
4.10 will be all you'll find unless you are a real lucky SOB.

03-27-2008, 01:07 AM	#1
eke82 Registered User Join Date: Dec 2006 Location: stromsburg ne Posts: 62	3.73 for eaton rearend? my dad and i have a 72 3/4 4x4 4spd with 4.10 he wants to put 3.73 in it for hiway but i dont thinK 3.73 are available for the eaton rearends but he tought they were

03-27-2008, 01:09 AM	#2
desertPOS Registered User Join Date: Sep 2007 Location: Arcadia, CA Posts: 78	Re: 3.73 for eaton rearend? pretty sure that's what I have in my '69 C20 ho52

03-27-2008, 01:23 AM	#3
stllookn Saving 1 truck at a time! Join Date: Aug 2001 Location: Kent, WA Posts: 6,465	Re: 3.73 for eaton rearend? 3.73 is the ratio in my Dana. Coincidence? __________________ '68 C20 Longhorn 50th Anniversary 400/TH400 '68 C20 Longhorn 50th Anniversary 468/TH400w/buckets '72 C20 Halfhorn (Longhorn w/o cab and front clip) '69 Flxible Cruiser (look up ugly in the dictionary)

03-27-2008, 01:25 AM	#4
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,851	Re: 3.73 for eaton rearend? 4.10 was the highest gear GM offered.There were 3.90s made at one time by outside sources.You can get 3.73s for the Dana44 and swap-in a 3.73 14-bolt.`72-earlier GMC trucks could have Dana60s with a higher gear,3.54?,or something like that.Whatever it is,that`s what my`72 Sierra has and it rolls along nicely with 12.50/33s(TH350).But,it gets the same mileage as my`72 Highlander with 4.10s and 12.50/35s(SM465). __________________ "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 ~ Last edited by special-K; 03-30-2008 at 05:35 AM.

03-29-2008, 02:54 AM	#5
mnunn454 Registered User Join Date: Dec 2006 Location: Rhode Island Posts: 602	Re: 3.73 for eaton rearend? I ordered and installed 3.73's and a new Eaton posi carrier a few years ago. Parts all easily obtainable. However, it you're after improved fuel mileage in a 4X4, dropping the ratio by 10% (4.11 down to 3.73 is about 10%) will net you a little savings, but not nearly enough (IMO) to pay for the gear swap costs. Said another way, if you spend $200 a month now in fuel and can reduce that by 10% with a gear swap, it'll take about 30 months (2.5 years) of driving before you've paid back the upgrade cost and start "saving" any money. Food for thought... __________________ 69 C-10 SWB Fleetside 454/TH400 (For Sale) http://67-72chevytrucks.com/vboard/c...ct=1299&cat=12 70 El Camino 454 TH700 29 Model A 4-DR Sedan Deluxe

03-29-2008, 03:53 AM	#6
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,851	Re: 3.73 for eaton rearend? Where did you find 3.73s for a Corporate rear?I`d like to talk to them. __________________ "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 ~

03-29-2008, 05:16 AM	#7
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: 3.73 for eaton rearend? I think he installed an eaton built assembly in his 1/2 ton 12 bolt. If you look at his siggy, he has a C/10. We are talking about the corperate rear/eaton diff rear that came stock in the C/20 & 30trucks. 4.10 will be all you'll find unless you are a real lucky SOB.

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