4x4 Guru's....I need some help

[superchevy]

I've got my '72 K25 down to the frame/susp and am trying to determine what is going on with this truck. First, is the front track supposed to be wider than the rear? Asking, because the front track on this truck is about 3" wider than the rear track. This leads to my next question....I'm wondering if the Dana 60 rear currently attached is the original one to this truck. Wondering, because the rear springs are not original...notice the rear hangers have been moved rearward, and welded...not riveted...to the frame....spring eye to spring eye is 56"...cleaning the frame today with degreaser, I ound that written on each leaf spring in salvage yard ink was " 74 C20 Chevy "...so the original 52" springs were replaced with these 1974 56" springs. The D-60 measures 53 1/2" from backing plate to backing plate....is this a stock '72 width, or do I have a '74 D-60. See the pics.
Appreciate any help on this issue.
Casey

[Dieselwrencher]

Casey, I have a 72 C20 I can measure the rear axle width tomorrow if that will help. I think ,ost of these 67-72 4x4 trucks were like you state, front wider than the rear. I don't know if it was due to the engineers thoughts of track and 4wd operation, or if it was an after thought. It might have been for turning radius as well. IDK But I think the 74 rear axle would be wider if anything. Unless it came from a cab chassis type truck. I bet it is the OE rear axle but I have been wrong before. I am guessing the spring hangers were moved to get the 56" springs in place. And instead of drilling new holes, they just welded the hangers back on.

[msgross]

4WD rear axles are always narrower on chevy's. Into the 80's they still did it even.... why? don't know for sure but i've heard the same (turning radius, tracking etc..)

3" sounds about right, 1.5" for each side...

[og350]

your right the front is correct for the truck. my 71 k20 is the same way. if i were you i would keep the 56" springs in the rear! they are longer and will ride better. good looking start keep us updated!!! good luck!

[desertrat]

I don't have any measurments but I had a 72 k20 and I replaced the Eaton rear end with a '76 14 bolt.
The rear track width ended up to be almost the same as the front, which looked nice.
I agree w/ og350 keep the longer springs on there.

[Stocker]

Maybe the front track is slightly wider to allow a tighter turning radius without the tires contacting the leaf springs?

[lowe137]

as far as i have read the reason for the track diffrence is for off road purpose...its so the rear tires wont ride in the ruts of the front tires... all chevys ive had have wider front track width

[fun in dirt]

If it is a Dana 60 rear, it is not O.E. to this truck. Are you sure it is not a Dana 70? The reason I'm asking is that single rear wheel 1-ton trucks and Dually trucks used these axles and this length springs. I know you said the junkyard had written 74 C-20 but these trucks in either 2 or 4 WD didn't use this axle. You can look on one of the gussets on the housing and look for "D70" casted into it. If you are sure it is a 60 then it probably came from under a Ford The only D60's Chevy used was in front. Look to see if there evidence of the rear spring perches being cut off,moved and re-welded and that would tell you if it was borrowed from another truck. I cannot comment on the track width as i've never paid attention to that measurement. Hope this helps.

[superchevy]

Thanks for all the info guys. I scraped off the D60 axle tube where the date code and BOM numbers are, and according to a D60 site I found, the 4 20 2 C, date code reads as April 20, 1972 3rd shift...so it is the original axle (fun in dirt, the D60 was available on the '72 3/4 tons). The tag on one of the diff cover bolts reads "4.10", which is also correct for the year. As for the longer springs, I am definitely keeping them.
Thanks again for all the help. It's good to know what I have.
Casey

[msgross]

This is a GMC not a chevy right? wouldn't that explain the dana60?

[Dooley]

GMC assembly definitely did some things different from Chevrolet, especially in 1972. Most all of us wish that they had documented their parts usage as well as Chevrolet did.

[Dieselwrencher]

I have parted out a few 69-72 K20 chevys and 2 had D60's and one had an eaton in the rear. Also, my Longhorn truck, which is 2wd, has a factory D60 in the rear.

[fun in dirt]

Originally Posted by superchevy

...so it is the original axle (fun in dirt, the D60 was available on the '72 3/4 tons).

Oops I had no idea...well, learn something new everyday!

[LONGHAIR]

Originally Posted by lowe137

as far as i have read the reason for the track diffrence is for off road purpose...its so the rear tires wont ride in the ruts of the front tires... all chevys ive had have wider front track width

That is what I have always understood to be the reason.

[1969 GMC]

My '69 GMC K2500 came stock with a D60 rear. It seems like the GMC's usually had them.