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Old 09-28-2008, 08:20 PM   #1
Jtrux
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1972 GMC 3/4 ton rear axle ????

A friend of mine (72LEVI) picked up a 72 3/4 ton GMC with a Dana rear axle. My question is, which one is it, a 60, 70 or ??? I don't know them a part by looking at them. Also I always hear of 3.54 gears in these axles, are those the only ones they came with?? Are they worth keeping in a truck?? If it's a 60 or 70 it should have lots of aftermarket support right??
Thanks.
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Old 09-28-2008, 10:45 PM   #2
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Re: 1972 GMC 3/4 ton rear axle ????

Should be stamped on one of the webs as viewed from the rear.
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Old 09-28-2008, 10:57 PM   #3
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Re: 1972 GMC 3/4 ton rear axle ????

Being a GMC it should be a leaf sprung Dana 60. 3:54 cogs is all I have ever seen but I am sure there were other gear ratios available.
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Old 09-28-2008, 11:06 PM   #4
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Re: 1972 GMC 3/4 ton rear axle ????

I might need to jack it up and turn wheels, mark driveshaft, etc... Jtrux is right its a Dana and other guys tell me its a 3.54 but Longhorn Man says it has rear suspension mods and most likely used as tow rig. The gears may have been changed, i will look. The leaf springs looked modded and it even has coils on shocks. See parts section, I am thinking Dana 60.
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Old 09-29-2008, 04:49 AM   #5
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Re: 1972 GMC 3/4 ton rear axle ????

You`d know a Dana70 from a D60 if you saw one.That would be a way big rear.Like comparing a D44 front to a D60 front.The D60 came in the lower 4.10 and 4.56 as well.You hear alot about the 3.54 because it`s unusual for back then and great for today`s needs.Was that a big block originally?I saw the pics you sent,nice truck for the money,and noticed a later small block was dropped in and it has alot of options.The 1/2t big blocks trucks with automatics only came with 3.08s.I`d assume a big block/auto 3/4t would only come w/3.54.
You`ll find a "60",as mentioned,on the lower web in the center section.
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Old 09-29-2008, 05:01 AM   #6
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Re: 1972 GMC 3/4 ton rear axle ????

tim, if you look at the photoi, it's a 3/4 ton (no 3.08 gears) and the truck has the remote power steering deal.
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Old 09-29-2008, 05:33 AM   #7
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Re: 1972 GMC 3/4 ton rear axle ????

Gotcha,but I already knew that and it shows in my post.I only mentioned the 1/2t BBC ratio as part of my reasoning for assuming it would be 3.54s "if" it was in fact a BBC originally.
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"BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed"......

'67 C1500 SWB Wideside Super Custom: 327/M22/3.42 posi...project 'Driver Quality'
(ground-up used truck)
'72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 PowerLoc...project 'Beefy Stock'-ish
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Old 09-29-2008, 02:31 PM   #8
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Re: 1972 GMC 3/4 ton rear axle ????

my bad man... I was scanning posts quickly before work.
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Old 09-29-2008, 02:39 PM   #9
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Re: 1972 GMC 3/4 ton rear axle ????

If that truck was originally a BB with a 4 speed transmission, it was probably a 4:10 (4:11) ratio. That's how my 72 Chevy longhorn BB was configured, with not option on spid IIRC. Granted mine was a 1 ton SRW so your mileage mary vary.
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Old 09-29-2008, 03:55 PM   #10
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Re: 1972 GMC 3/4 ton rear axle ????

I dont want to hijack , but i have the same problem .68 gmc 1/2 ton 250 six
im sure its a dana it has 354 gear. But i don't know which dana ? can someone post pictures of the different ones . My spid is gone .
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Old 09-29-2008, 04:12 PM   #11
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Re: 1972 GMC 3/4 ton rear axle ????

Quote:
Originally Posted by Longhorn Man View Post
my bad man... I was scanning posts quickly before work.
gettin old...bud
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Old 09-29-2008, 04:20 PM   #12
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Re: 1972 GMC 3/4 ton rear axle ????

My 72 GMC (model noted as "wideside pickup" on title), 402 BB/T400 equipped C 3500 pickup had 3.73 Eaton rear gear. This was a special order truck with factory tach, spotlight, passenger side underbed toolbox, drivers side underbed fuel tank, rear overload springs and was a 8.5' bed. It was Fleet yellow with black interior. I had owned a 69 C20, 396/T400 Longhorn previous to this truck.

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Old 09-29-2008, 06:54 PM   #13
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Re: 1972 GMC 3/4 ton rear axle ????

3.54 Dana 60; yes there's some lube on the inside as well. At one time, it had a metal tag with 3.54 stamped on it.
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Old 09-29-2008, 07:51 PM   #14
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Re: 1972 GMC 3/4 ton rear axle ????

3.54 was the standard gear on all big block 3/4 tons, 3 speed, 4 speed, or auto. It was not even avalible on one tons.
Dooley, do you have a spid showing your 3.73 gear? Or was that simply what you found in yours? Now granted, yours is a GMC, and there is little to no documentation on them, but chevy doesn't show 3/73 anywhere for any 3/4 or one ton trucks at all in the 67 - 72years.
dfosh, can you show a pic of your diff? If it's a dana, it should be a 60 (assuming 2 wheel drive here) and I've only heard of one 3.54 that was not in a big block truck... claimed to be original (a respected member, the ONLY reason I believe it is true)
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Old 09-29-2008, 08:03 PM   #15
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Re: 1972 GMC 3/4 ton rear axle ????

For some reason, Chevy never offered the 3.73 ratio on the C-20 Dana 60 3/4 tons between 68-72, while Dodge and Ford used this ratio in their Dana 60 3/4 tons.
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Old 09-29-2008, 09:13 PM   #16
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Re: 1972 GMC 3/4 ton rear axle ????

our trucks never got dana 70's, either. to visually id a 60 from a 70, the lip on the casting sticks farther down past the diff cover on a 70 than the 60, if for some reason you can't see or find any numbers.
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Old 09-29-2008, 09:32 PM   #17
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Re: 1972 GMC 3/4 ton rear axle ????

My`72 K2500 has 3.54s and a 350.There were 1/2t Dana60s in some GMCs.

Andy,no problem.I hope I didn`t come off wrong there.Besides,it`s not like I make sense all the time.We should get together and check out rears sometime.
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"BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed"......

'67 C1500 SWB Wideside Super Custom: 327/M22/3.42 posi...project 'Driver Quality'
(ground-up used truck)
'72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 PowerLoc...project 'Beefy Stock'-ish
(Still original)
'85 K5/25 Jimmy Sierra: 6.2/700r4/4.10 Locker/8-lugs...project 'Jimmy'
(li'l helper,peeps hauler,& fun machine)
Tim

R.I.P. East Side Low Life ____________ R.I.P. El Jay__
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Old 09-29-2008, 09:35 PM   #18
Longhorn Man
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Re: 1972 GMC 3/4 ton rear axle ????


OK, 2 ppl that I trust about these trucks that have 3.54 rears in non big block trucks.
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Old 09-29-2008, 10:20 PM   #19
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Re: 1972 GMC 3/4 ton rear axle ????

To your credit,I always thought they were 3.73s until you told me GMC didn`t offer that and did offer 3.54s.I never knew that.I checked mine and there they were.So,if you hadn`t corrected me you`d be right.(now,about what I said about me not making sense sometimes)
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"BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed"......

'67 C1500 SWB Wideside Super Custom: 327/M22/3.42 posi...project 'Driver Quality'
(ground-up used truck)
'72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 PowerLoc...project 'Beefy Stock'-ish
(Still original)
'85 K5/25 Jimmy Sierra: 6.2/700r4/4.10 Locker/8-lugs...project 'Jimmy'
(li'l helper,peeps hauler,& fun machine)
Tim

R.I.P. East Side Low Life ____________ R.I.P. El Jay__
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Old 09-30-2008, 07:50 AM   #20
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Re: 1972 GMC 3/4 ton rear axle ????

I will post pic tommrow night . My son will have to do it for me . I did look at it again after seeing the above pic. Mine had a 4 on the web maybe a 44 as i could not make out the second # .tag on the cover was 46-13 3.54 . It also still had the paper sticker around the axel tube next to the backing plate .It was covred in dirt kinda brittle when i was cleaning .Number on it was 3903540 . Hope it showes in the pic when i post them. This truck was from the person that bought it new .
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Old 09-30-2008, 09:58 AM   #21
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Re: 1972 GMC 3/4 ton rear axle ????

46 and 13 are the tooth counts on the ring and pinion, respectively.

46/13 = 3.538 or your 3.54:1 ratio.
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Old 09-30-2008, 12:03 PM   #22
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Re: 1972 GMC 3/4 ton rear axle ????

3:54 definitely was the standard gear as Longhorn man stated. Come to think of it I have never owned a single 67-72 two wheel drive that didn’t have 3:54 gears… Here is a few of the junk I have owned or still own.

1968 GMC C1500 305 V6/SM435 Dana 44 3:54 (parted). This truck’s rear axle is temporarily in my other ’68 GMC when the Dana 60 broke.

1968 GMC C1500 396BB/TH400 Dana 60(semi-floater: Rare) 3:54 (still have) Still have the broken semi-float Dana 60 as well. Something about those hard 1-2 TH400 shifts will a full race shift kit that tends to knock teeth off ring gears

1970 Chevy C10 402BB/SM465 Dana 44 3:54 (sold)

1972 Chevy C20 350/TH350 Eaton not sure of the gear ratio but the highway RPM’s are consistent of 3:54 (still have). I’ll have to chisel off the axle grime and look for a tag someday.

1972 K5 Blazer 3:73....4x4's were a different ball of gear wax anyway.
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