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#1 |
Registered User
Join Date: Feb 2018
Location: Cannon Beach, Oregon
Posts: 13
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1972 K20 rear end question
Hey guys, so I'm a fairly smart guy, but when it comes to rear diffs...I don't know squat.
![]() I have an Eaton open diff in the rear of my 1972 K20. I've been told if I'm interested in a locking/posi/etc rear diff, I should consider a Dana 60. I have pretty tall gears (4.56) in the Eaton, I'd like something a little more road friendly - 4.11 or 3.86 maybe? So, what do I look for? What year range with what gears, etc.? What are the details I need to know to buy the right thing? Thanks in advance for any guidance! I appreciate it. -Retro |
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#2 |
Registered User
Join Date: Nov 2014
Location: Southwest Kansas
Posts: 306
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Re: 1972 K20 rear end question
DANA 60 is a great choice, wide range of gears and pretty much bolt in up to '72 after that they changed spring perches and shock mounts, I think, but that can be changed with a little fab work. Another option would be a 14 bolt SF out of 70's and 80's 3/4-ton and 1-ton trucks, again lots of different gears and spring perches and shock mounts need to be changed. Both are great axles and parts are readily available.
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'64 C10 LWB, 283, 5speed '68 C20 LWB, 327, 4speed '69 C20 Custom Camper Longhorn, 350, 4speed '72 C20 Cheyenne Super, 396, TH400 '66 C60, 292, 4speed |
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#3 |
Registered User
Join Date: Dec 1999
Location: Austin, TX, USA
Posts: 7,721
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Re: 1972 K20 rear end question
4.10 were available for the Eaton but not as common as the 4.57. They were available with a Maximum Traction rear diff which was a true Locker. You can swap a Detroit into the case if you use 30 spline 14 bolt full float axle shafts.
There is an HO52/72 thread at Pirate4x4.com that is loaded with info on the Eaton. If I was swapping, I would just get a newer 14 bolt. Full float if you really work your truck hard, but the semi-float 14 from a 3/4 ton 4x4 Suburban can be a good choice. It is rated same as the HO52 in terms of GAWR and was used in vehicles up to 8600# GVWR which was higher than any of the C20’s which maxed at 7500#. I did this swap in my Jimmy years ago to get rid of the 12 bolt grenades I kept throwing. We just swapped another into my kid’s Jimmy project. My Suburan donor had 4.10 gears and his had 3.73. We swapped the 10 bolt front into his truck as well with a TransAm posi traction, but I just bolted the hub and brake parts from the 10 bolt onto my Dana 44.
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44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax |
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#4 |
All about them K’s
![]() Join Date: Jun 2014
Location: Land of Entrapment
Posts: 6,401
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Re: 1972 K20 rear end question
I put a 14 bolt full floater into my 72 K20. My truck has 4:11’s so it wasn’t hard for me to find a matching rear end. If you go this route you’ll have to strip the factory perches and shock mounts from the 14 bolt and re-weld everything back in the right locations for the narrower 72 spring locations. If you can find a square body 1 ton 4x4 srw, that axle will bolt in minus one shock mount.
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Tyler '57 3100 http://67-72chevytrucks.com/vboard/s...d.php?t=813888 '72 K20 Cheyenne: 5” lift, 35’s, front dana 60 blah blah blah… http://67-72chevytrucks.com/vboard/s...d.php?t=662879 ‘69 K10 SWB: 4” lift 33”s… in a million pieces http://67-72chevytrucks.com/vboard/s...d.php?t=805206 '98 Silverado LT K2500HD ECLB Vortec 454/4l80E: 6" lift 35x12.5x20’s |
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#5 |
Registered User
Join Date: Feb 2015
Location: Schaefferstown, PA
Posts: 202
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Re: 1972 K20 rear end question
I would go with a 14 bolt full floater. I have 4.10 gears in my 1970 k20. Well worth the work of cutting and remounting spring perches and shock mounts. 14 bolts are a dime a dozen and are strong rears. I work my truck really hard and prefer the 14 bolt over the Eaton. I Had 2 Eaton’s in my truck before I got smart and decided to do the swap.
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1970 Chevy K20 pulling truck 406 small block 1967 Chevy K20 daily/street truck My daily 1970 k20 - http://67-72chevytrucks.com/vboard/s...=1#post7568564 |
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#6 |
Special Order
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Location: Mt Airy, MD
Posts: 85,858
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Re: 1972 K20 rear end question
4.10 was the best hiway ratio offered by GM in the Dana 60, same as HO52. So no advantage going to Dana 60 unless you find a Ford rear with 3.73 to swap gear set or convert housing for GM mounting. Add to that the brake parts are getting hard to find, same as HO52, I would consider going 14-bolt. There were even 3.42s available.
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"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 ~ |
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#7 |
Registered User
Join Date: Feb 2018
Location: Cannon Beach, Oregon
Posts: 13
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Re: 1972 K20 rear end question
Thanks guys! Great info! I'm heading to the Portland Swap Meet on Friday morning and will start hunting (besides looking for a tailgate). I appreciate the data!
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#8 |
Registered User
Join Date: Apr 2011
Location: Klein Texas
Posts: 3,852
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Re: 1972 K20 rear end question
Since you have a K20 you will want the front and rear axle ratios to match.
4:56 in front and 4:10 in rear no bueano PO put a 14 bolt in my K20 but it had a 3:73. I decided to change the front to 3:73 also. I like it.
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My Classics: '72 K20 Suburban + '65 Dodge Town Wagon '72 Corvette Roadster +'67 Corvette Roadster '73 Z-28 Camaro '63 Ford SWB Uni Pickup '50 Ford Coupe |
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#9 |
Registered User
Join Date: Feb 2018
Location: Cannon Beach, Oregon
Posts: 13
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Re: 1972 K20 rear end question
Thanks, Dave. Very good point.
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#10 |
Registered User
Join Date: Nov 2014
Location: Southwest Kansas
Posts: 306
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Re: 1972 K20 rear end question
Special-K, with all due respect, but I'm pretty sure the 3/4-tons with big block and th-400 had 3.54's in the Dana 60 as standard equipment, at least in '72.
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'64 C10 LWB, 283, 5speed '68 C20 LWB, 327, 4speed '69 C20 Custom Camper Longhorn, 350, 4speed '72 C20 Cheyenne Super, 396, TH400 '66 C60, 292, 4speed |
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#11 |
Senior Member
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Location: Godley, TX
Posts: 17,963
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Re: 1972 K20 rear end question
While C20s indeed required a 3.54 D60 when a 402 was ordered (and a D60 was also possible when rear leafs were ordered on a C20, even with a small block), K20s came only with 4.57 standard or 4.10 optional. There were no big block K's and there are no 3.54s available for the front D44, at least not that I'm aware.
But if there are, that might be a pretty nice setup assuming tires aren't much bigger than stock and you are only planning on highway driving - in which case I'd direct you to the "C" line of 2WDs that GM offered ![]() ![]() Last edited by jocko; 04-04-2018 at 10:02 PM. |
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#12 |
Registered User
Join Date: Feb 2018
Location: Cannon Beach, Oregon
Posts: 13
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Re: 1972 K20 rear end question
Thanks, Jocko. I have the standard 4.56 front/rear and the TH350. I was kinda thinking 4.10 might be my target. Right now the truck has a 2" soft ride lift from Tuff Country and 33's. I'm thinking the 4.10s might be a good compromise - street/trail.
I really appreciate all the comments - this is learning curve. Thanks everyone! |
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#13 |
Special Order
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Location: Mt Airy, MD
Posts: 85,858
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Re: 1972 K20 rear end question
Yeah, I was talking about K/20s with rear ratios. The big block C/20s came with 3.54s but no 3.54 for the front axle.
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"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 ~ |
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#14 |
Carpe manana
![]() ![]() Join Date: Dec 2010
Location: Eau Claire, WI
Posts: 12,401
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Re: 1972 K20 rear end question
Minor point but wasn't a 4.10 ratio standard on AC equipped K20s?
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1972 K5 CST Highlander Blazer: http://67-72chevytrucks.com/vboard/s...d.php?t=708547 1972 K20 Cheyenne Super: http://67-72chevytrucks.com/vboard/s...d.php?t=528308 ![]() |
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#15 |
Registered User
Join Date: Jan 2011
Location: Townsend MT
Posts: 1,725
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Re: 1972 K20 rear end question
My '72 K20 came factory with 4.10's and nothing listed on the SPID pertaining to gear ratio...
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#16 |
All about them K’s
![]() Join Date: Jun 2014
Location: Land of Entrapment
Posts: 6,401
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Re: 1972 K20 rear end question
There might be something to this Pete. My 72 has factory 4:10s and ac, with no ratio call out on the spid. Honestly I just assumed that 4:10 was standard with a small block.
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Tyler '57 3100 http://67-72chevytrucks.com/vboard/s...d.php?t=813888 '72 K20 Cheyenne: 5” lift, 35’s, front dana 60 blah blah blah… http://67-72chevytrucks.com/vboard/s...d.php?t=662879 ‘69 K10 SWB: 4” lift 33”s… in a million pieces http://67-72chevytrucks.com/vboard/s...d.php?t=805206 '98 Silverado LT K2500HD ECLB Vortec 454/4l80E: 6" lift 35x12.5x20’s |
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#17 |
Registered User
Join Date: Apr 2011
Location: Klein Texas
Posts: 3,852
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Re: 1972 K20 rear end question
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My Classics: '72 K20 Suburban + '65 Dodge Town Wagon '72 Corvette Roadster +'67 Corvette Roadster '73 Z-28 Camaro '63 Ford SWB Uni Pickup '50 Ford Coupe |
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#18 |
Registered User
Join Date: Feb 2018
Location: Cannon Beach, Oregon
Posts: 13
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Re: 1972 K20 rear end question
I'm probably the one clouding this up. My truck is a CE - started life as a C20 Custom Deluxe. Came to me as a 4x4 - and given the larger front axles/u-joints, appears to be a '73 or later front end. It was a small block 350, but someone dropped a small block 400 in it. Still has the TH350. So, I'm ASSUMING the rear end was the original Eaton w/ 4.56s. However, my truck is an AC cab, so the AC and 4.10 comment makes me wonder if someone swapped the rear end too. Anyway, the result is an Eaton open diff rear end w/ 4.56 and the front ratio matches. I always call it a K20, but in truth it's a C20 (for factory options considerations). Sorry if I misled.
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'72 K20 Custom Deluxe '95 2500 Suburban 454cu in |
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#19 |
Senior Member
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Location: Colfax-California
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Re: 1972 K20 rear end question
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#20 |
Registered User
Join Date: Apr 2011
Location: Klein Texas
Posts: 3,852
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Re: 1972 K20 rear end question
The chart I posted above says 350 got a 4.10 standard and 307 got 4.57 standard
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My Classics: '72 K20 Suburban + '65 Dodge Town Wagon '72 Corvette Roadster +'67 Corvette Roadster '73 Z-28 Camaro '63 Ford SWB Uni Pickup '50 Ford Coupe |
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#21 |
Moderator
![]() Join Date: May 2007
Location: Southern Cal
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Re: 1972 K20 rear end question
Mine is 4:10 with a power lock, ac equipped. Power lock is called out on spid, gear ratio is not. I verified physically after checking one of sstims power team charts.
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1972 C/10 Cheyenne Super SWB. Restored, loaded, slammed. 1968 C/10 50th Anniversary LWB. Unrestored, stock, daily driver/work truck. RIP ElJay RIP 67ChevyRedneck RIP Grumpy Old Man |
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#22 |
Registered User
Join Date: Dec 2007
Location: Van Buren Arkansas
Posts: 137
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Re: 1972 K20 rear end question
72 K20.....no ac 410 eatons
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1972 Cheyenne Super..owned since 1978 1972 Surburban 4x4 1972 Cheyenne 4x4 3/4 ton.....sold 1972 Cheyenne 2wd...named Death Row |
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#23 |
Registered User
Join Date: Dec 1999
Location: Austin, TX, USA
Posts: 7,721
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Re: 1972 K20 rear end question
3.54 are certainly available for the Dana 44 through aftermarket if wanting to go to lower gear. And I’ve looked at a couple of different K10 ‘67 GMC V6 powered trucks that had 3.54 gears. Not only that, they had Dana 44 in both ends.
Cheapest thing to do would be find donor K20 Suburban with 3.73 and swap both axles in to your truck. But the option of just sourcing a rear and then changing gears in front is another option. Any problem can be solved by throwing enough $ at it!
__________________
44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax |
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#24 |
Special Order
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Location: Mt Airy, MD
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Re: 1972 K20 rear end question
I was sticking with K/20 information. There are all sorts of possibilities for gear ratios through gear set swaps and/or complete axle swaps from other vehicles or aftermarket.
I don't know about the A/C thing with 4.10s, but I have never seen a K/20 with 350/TH350 that didn't have 4.10s.
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"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 ~ |
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