Eaton Rearend - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Madbomber88 · 04-01-2006, 03:43 PM

I just picked up a 72 K20 and it supposedly has an Eaton rearend (big and round). What does this mean? Pros/Cons? I have heard that this means I have very limited ring and pinion options. I would love to swap out what I have, (think they are 4.56) for some 3.73s or something so I can at least drive it on the highway. I am having a very hard time finding any info about these rearends. Any info is appreciated.

1969 GMC · 04-01-2006, 03:58 PM

Try searching this site, especially the 4x4 page. You should find everything you need.

*wolfthing2000* · 04-01-2006, 04:25 PM

you can find a 4.10 rear center section and bolt her in. I don't believe there are any higher geared than that. Remember, it is a tuck axle.

1969 GMC · 04-01-2006, 04:58 PM

there is a 3.90 aftermarket gearset available.

Madbomber88 · 04-01-2006, 05:02 PM

I saw something about the 3.90 ring and pinion, but I can't find it for sale anywhere. The one place that did, had it listed as no longer being made. How would the 3.90 work with the front differential? Do they make a 3.90 for that too?

Maybe it's better to swap in a Dana 60?

wibilly · 04-01-2006, 10:56 PM

i'v been told that 14 boltff caierers will fit the eatons but you must use the 14 bolt axels which will need to be shortened an inch or inch and a half then some machining is require for outer axel bearings more info is avalibale on pirate 4x4 message board.

**special-K** · 04-01-2006, 11:58 PM

4.10 to 3.90 ain`t worth it in my book.It`s a small difference.I`ve been driving trucks with HO52s for over 30 years on the hiway.I`d go with o/d to drop the rpms.

Madbomber88 · 04-02-2006, 08:14 AM

ok, I think it is 4.56 right now. It's a 4x4 with a 350 SM465. Is overdrive even an option?

Steelawork'n · 04-02-2006, 08:31 PM

You can keep your same rearend and tranny and go with a GearVenders Over/Underdrive unit.

*wolfthing2000* · 04-02-2006, 08:40 PM

bigger rubber!

JAKES 68GMC · 04-02-2006, 09:07 PM

IIRC, Jim carters truck parts has the 3.90 gears, but they are a good chunk of change.

I'd probably go with a D60. Parts for them are common, and if you look around, I think you can find 3.21 and numerically lower ratio's.

Madbomber88 · 04-02-2006, 09:39 PM

You'd really go with a D60 over the 14 bolt? I have 8 lugs right now. Pros/con for D60 and 14 Bolt?

JAKES 68GMC · 04-02-2006, 10:13 PM

A Dana 60 is a 8-lug full-floater rear. I don't know much about the 14 bolt though.

04-01-2006, 03:43 PM	#1
Madbomber88 Active Member Join Date: Mar 2004 Location: Virginia Posts: 169	Eaton Rearend I just picked up a 72 K20 and it supposedly has an Eaton rearend (big and round). What does this mean? Pros/Cons? I have heard that this means I have very limited ring and pinion options. I would love to swap out what I have, (think they are 4.56) for some 3.73s or something so I can at least drive it on the highway. I am having a very hard time finding any info about these rearends. Any info is appreciated. __________________ 71 Blazer CST 72 K20 Capt USAF

04-01-2006, 03:58 PM	#2
1969 GMC Registered User Join Date: Feb 2003 Location: The Rubber City Posts: 5,498	Re: Eaton Rearend Try searching this site, especially the 4x4 page. You should find everything you need. __________________ 1969 GMC K2500 1996 Honda Accord 2007 Kawasaki KLR 650

04-01-2006, 04:25 PM	#3
wolfthing2000 Account Suspended Join Date: Oct 2004 Posts: 1,276	Re: Eaton Rearend you can find a 4.10 rear center section and bolt her in. I don't believe there are any higher geared than that. Remember, it is a tuck axle.

04-01-2006, 04:58 PM	#4
1969 GMC Registered User Join Date: Feb 2003 Location: The Rubber City Posts: 5,498	Re: Eaton Rearend there is a 3.90 aftermarket gearset available. __________________ 1969 GMC K2500 1996 Honda Accord 2007 Kawasaki KLR 650

04-01-2006, 05:02 PM	#5
Madbomber88 Active Member Join Date: Mar 2004 Location: Virginia Posts: 169	Re: Eaton Rearend I saw something about the 3.90 ring and pinion, but I can't find it for sale anywhere. The one place that did, had it listed as no longer being made. How would the 3.90 work with the front differential? Do they make a 3.90 for that too? Maybe it's better to swap in a Dana 60? __________________ 71 Blazer CST 72 K20 Capt USAF

04-01-2006, 10:56 PM	#6
wibilly Senior Member Join Date: Nov 2005 Location: northwestern wi Posts: 2,111	Re: Eaton Rearend i'v been told that 14 boltff caierers will fit the eatons but you must use the 14 bolt axels which will need to be shortened an inch or inch and a half then some machining is require for outer axel bearings more info is avalibale on pirate 4x4 message board. __________________ common sense isn't so common anymore

04-01-2006, 11:58 PM	#7
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,852	Re: Eaton Rearend 4.10 to 3.90 ain`t worth it in my book.It`s a small difference.I`ve been driving trucks with HO52s for over 30 years on the hiway.I`d go with o/d to drop the rpms. __________________ "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 ~

04-02-2006, 08:14 AM	#8
Madbomber88 Active Member Join Date: Mar 2004 Location: Virginia Posts: 169	Re: Eaton Rearend ok, I think it is 4.56 right now. It's a 4x4 with a 350 SM465. Is overdrive even an option? __________________ 71 Blazer CST 72 K20 Capt USAF

04-02-2006, 08:31 PM	#9
Steelawork'n Just hang'n around Join Date: Nov 2005 Location: Camano Island WA Posts: 248	Re: Eaton Rearend You can keep your same rearend and tranny and go with a GearVenders Over/Underdrive unit. __________________ Driving a '68 Chevy C20 and a '93 Astro Van. Lots and lots of mileage that I deduct each year.

04-02-2006, 08:40 PM	#10
wolfthing2000 Account Suspended Join Date: Oct 2004 Posts: 1,276	Re: Eaton Rearend bigger rubber!

04-02-2006, 09:07 PM	#11
JAKES 68GMC Aluminum slot wheels rule... Join Date: Jan 2006 Location: Maine Posts: 6,212	Re: Eaton Rearend IIRC, Jim carters truck parts has the 3.90 gears, but they are a good chunk of change. I'd probably go with a D60. Parts for them are common, and if you look around, I think you can find 3.21 and numerically lower ratio's. Last edited by JAKES 68GMC; 04-02-2006 at 09:13 PM.

04-02-2006, 09:39 PM	#12
Madbomber88 Active Member Join Date: Mar 2004 Location: Virginia Posts: 169	Re: Eaton Rearend You'd really go with a D60 over the 14 bolt? I have 8 lugs right now. Pros/con for D60 and 14 Bolt? __________________ 71 Blazer CST 72 K20 Capt USAF

04-02-2006, 10:13 PM	#13
JAKES 68GMC Aluminum slot wheels rule... Join Date: Jan 2006 Location: Maine Posts: 6,212	Re: Eaton Rearend A Dana 60 is a 8-lug full-floater rear. I don't know much about the 14 bolt though.

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