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Old 03-04-2019, 10:32 PM   #1
72 k15
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78 axles in 72?

Will a 14 bolt axle and dana 44 out of a 78 fit in a 72 gmc k15? Wanted to buy them for the 4.10 gearing they have and put em in as a upgrade. Looks like i saw the front will go right in but the rear perches will need to be moved?

Last edited by 72 k15; 03-04-2019 at 10:37 PM.
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Old 03-05-2019, 04:31 PM   #2
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Re: 78 axles in 72?

I think your correct..the fronts will bolt right in...rear spring perches will need moved....just pull a tape on the rear center2center on both and it'll let you know...
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Old 03-05-2019, 05:02 PM   #3
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Re: 78 axles in 72?

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Originally Posted by mongocanfly View Post
I think your correct..the fronts will bolt right in...rear spring perches will need moved....just pull a tape on the rear center2center on both and it'll let you know...
I was wondering Beacuase the guy I am buying them from says they will just drop in.
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Old 03-05-2019, 05:31 PM   #4
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Re: 78 axles in 72?

I know my 91 k20 14bolt and my 67 k20 eaton are different width spring pads....
The front swapped with no issue...had to move the rear spring pads...I'd just git him to measure it to compare it to yours...moving spring pads isn't a big deal...just cut the old ones off and weld on a new set..
And the wms 2 wms is different as well...
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Old 03-05-2019, 07:42 PM   #5
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Re: 78 axles in 72?

The 3/4 ton14 bolt will require spring perch relocation and a 1 ton 14 bolt is a direct bolt in
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Old 03-06-2019, 09:43 PM   #6
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Re: 78 axles in 72?

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Originally Posted by mongocanfly View Post
I know my 91 k20 14bolt and my 67 k20 eaton are different width spring pads....
The front swapped with no issue...had to move the rear spring pads...I'd just git him to measure it to compare it to yours...moving spring pads isn't a big deal...just cut the old ones off and weld on a new set..
And the wms 2 wms is different as well...
Forgive me but what does wms mean? And could I just weld the perches to the angle on the old axle or do I have to do some double knot ciphering to get it rihgt?
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Old 03-06-2019, 09:53 PM   #7
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Re: 78 axles in 72?

wms = wheel mount surface .
srw = single rear wheel .
drw = duel rear wheel .
c&c = cab & chassis . narrowest width rear of the 14ff .
14ff = 14 bolt full floater axle .

there is srw and drw then drw c&c for 14ff axles .

so if you can post up pics before you buy so we can help you get the correct stuff .

and if no lift kit or stuff like that then yes you can weld the perches to the same angle as the old axle .

there is super beefy aftermarket leaf spring perches out there that work better than old and are cheeper than new stock style wimpy ones . and no need to save the old when there so cheep .

barnes 4x4 has them . sells a lot on ebay .
ruff stuff specialtys has them .
diy4x.com has them .
offroad design has them .

some places have axle swap kits with perches / spring plates / u-bolts / shock mounts all in 1 package deal .
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Old 03-06-2019, 09:56 PM   #8
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Re: 78 axles in 72?

I built a lightweight jig off my original perches to align the shock mounts then i just put the new perches on at the same pinion angle as the original setup at the original width.

No measurement origami.
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Old 03-06-2019, 10:17 PM   #9
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Re: 78 axles in 72?

Quote:
Originally Posted by sweetk30 View Post
wms = wheel mount surface .
srw = single rear wheel .
drw = duel rear wheel .
c&c = cab & chassis . narrowest width rear of the 14ff .
14ff = 14 bolt full floater axle .

there is srw and drw then drw c&c for 14ff axles .

so if you can post up pics before you buy so we can help you get the correct stuff .

and if no lift kit or stuff like that then yes you can weld the perches to the same angle as the old axle .

there is super beefy aftermarket leaf spring perches out there that work better than old and are cheeper than new stock style wimpy ones . and no need to save the old when there so cheep .

barnes 4x4 has them . sells a lot on ebay .
ruff stuff specialtys has them .
diy4x.com has them .
offroad design has them .

some places have axle swap kits with perches / spring plates / u-bolts / shock mounts all in 1 package deal .
Picture from the seller.
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Old 03-06-2019, 10:37 PM   #10
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Re: 78 axles in 72?

14 bolt full floater...I also see some front axle parts laying in the floor along with rear axle parts..are you buying them in the torn apart state?....I would be Leary of something somebody tore apart and stuck back together....unless I really knew the axle owner...
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Old 03-06-2019, 10:48 PM   #11
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Re: 78 axles in 72?

Quote:
Originally Posted by mongocanfly View Post
14 bolt full floater...I also see some front axle parts laying in the floor along with rear axle parts..are you buying them in the torn apart state?....I would be Leary of something somebody tore apart and stuck back together....unless I really knew the axle owner...
I am kinda Leary also he wants 350 for Dana 44 and 14 bolt only want them for the 4:10s would be cheaper than rebuilding mine. So I see I need to move the perches then?
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Old 03-06-2019, 11:06 PM   #12
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Re: 78 axles in 72?

I'm gonna say yes..spring perch needs moved..and probably the shock mounts as well...only way to know for sure what needs done is pull a tape on it.....
Something else I wonder about is the driveshaft length.....
also the total axle width will be wider (I think) than your axles...if you've got a Eaton axle seems like I saw that gears aren't being made for the anymore....( again,I think)... ..
350 is cheap enough...but it would scare me that he tore them apart..and why...
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Old 03-06-2019, 11:32 PM   #13
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Re: 78 axles in 72?

Quote:
Originally Posted by mongocanfly View Post
I'm gonna say yes..spring perch needs moved..and probably the shock mounts as well...only way to know for sure what needs done is pull a tape on it.....
Something else I wonder about is the driveshaft length.....
also the total axle width will be wider (I think) than your axles...if you've got a Eaton axle seems like I saw that gears aren't being made for the anymore....( again,I think)... ..
350 is cheap enough...but it would scare me that he tore them apart..and why...
I honestly donít think all that would be worth it I might just put some 4:10s in my axles instead. Who makes some rebuild kits and gears that wonít take my wallet unlike Yukon, although if they make good stuff might buy from them.
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Old 03-06-2019, 11:38 PM   #14
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Re: 78 axles in 72?

Do you know what axles you have...front and rear...?....Yukon makes great stuff
What gears do you have now?...also tire size and trans you have?
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Old 03-06-2019, 11:48 PM   #15
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Re: 78 axles in 72?

Quote:
Originally Posted by mongocanfly View Post
Do you know what axles you have...front and rear...?....Yukon makes great stuff
What gears do you have now?...also tire size and trans you have?
Danna 44 and 12 bolt Orginal Posi gearing tag says 3.07. Going to be running 33s and nv4500.
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Old 03-07-2019, 12:11 AM   #16
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Re: 78 axles in 72?

You'll have to change the rear diff/locker as well to go from 3.07 to 4.10s...12bolt series 3 to series 4..
Your close with your ratio choice...I'm running 33s with a nv but I went 4.56s
Youd be better off buying the axles already setup from another truck...
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Old 03-07-2019, 01:51 AM   #17
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Re: 78 axles in 72?

Installing the 14 bolt, aside from moving the spring perches, you will also have to move the shock mounts and mess with the parking brakes cables. You will also have to freshen up the rear driveshaft and install either a conversion joint or just go 1350 series with the driveshaft mod.
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Old 03-07-2019, 02:08 AM   #18
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Re: 78 axles in 72?

I have to second the Barnes4x4 stuff also. I used there jeep kit to install a Ford 8.8 in a Jeep TJ. Kit was outstanding other than the directions for locating the brackets. They also sell on Amazon. That is where I bought the kit at since it was actually the cheapest there.
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Old 03-09-2019, 06:00 PM   #19
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Re: 78 axles in 72?

Quote:
Originally Posted by mongocanfly View Post
You'll have to change the rear diff/locker as well to go from 3.07 to 4.10s...12bolt series 3 to series 4..
Your close with your ratio choice...I'm running 33s with a nv but I went 4.56s
Youd be better off buying the axles already setup from another truck...
You said I have to get different carriers I thought Yukon made 4.10s that fit the 3.73 and down carriers front and rear?
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Old 03-10-2019, 08:31 AM   #20
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Re: 78 axles in 72?

not sure about Yukon but I think Richmond makes what they call a thick gear 4.10 for a series 3....
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Old 03-10-2019, 10:16 AM   #21
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Re: 78 axles in 72?

Several manufacturers make the thick gears. But I would take advantage of the opportunity to upgrade to the 3/4 ton axles if it were mine. And I did with a set of 4.10 geared axles from an Ď86 3/4 ton Suburban. I used the semi-float rear though. After breaking 6 different 12 bolts one way or the other in my Jimmy this has been one of the better upgrades I have done. You may have to shorten the driveshaft if you arenít running any lift in your truck, but I would recommend drilling a new locator hole in the spring perch and moving the rear axle back one inch. That better centers it in the wheelwell any how. You will be paying to have custom shafts made for both ends anyhow when you swap the NV4500 in.
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Old 03-20-2019, 08:58 PM   #22
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Re: 78 axles in 72?

Quote:
Originally Posted by 72 k15 View Post
I was wondering Beacuase the guy I am buying them from says they will just drop in.
Like someone else said, you will have to move the spring perches and the shock mounts are different also,and have to be moved, I did this in my 72, not that big of a deal, but the shock bolt holes are bigger on the 3/4 ton axle, I just welded a washer on each side of the shock mount that had a little smaller hole in it....
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Old 04-08-2019, 04:18 AM   #23
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Re: 78 axles in 72?

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Like someone else said, you will have to move the spring perches and the shock mounts are different also,and have to be moved, I did this in my 72, not that big of a deal, but the shock bolt holes are bigger on the 3/4 ton axle, I just welded a washer on each side of the shock mount that had a little smaller hole in it....
The shock mount holes are often forgot on this swap.

I have both welded washers, cut hangers and replaced them as well as ordered them from a race car shop such as Stockcar products, etc..

Good call, the small details of the shock mount hole is often overlooked.

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