65 K20 4x4 axle/differential replacement

[Submariner616]

My '65 K20 has the original stock 455/456 gears in the two differentials. Two local well known shops in Phoenix area have said there is nothing available to reduce the gear ratio to, say, 373. The suggested option is to swap out the axles with ones from maybe a '69 through '80. Has anyone done this or know what year trucks have comparable axles to use?

[350TacoZilla]

Your not going to find gears new on the shelf to get 3.73 or 4.10 setup but there are 4.10 versions of your old axles if you were really wanting to keep it original. That being said if you dont care about that part of it then yeah you can always just bolt another full set of axles in from a newer truck. Almost any of the 67+ 3\4Ton 4x4 axles will be an upgrade in the braking and also in parts availability but my first choice would be to use a set from a 73-87 K20 and to avoid the 9.5 SF 14 bolt rear, its not a bad axle really but the more common 14 bolt FF rear is much stronger with better parts availability which is what got you into this swap in first place. If you want a big upgrade in strength up front you could go with K30 axles instead and get a dana 60 front but the K20 dana 44 or 10 bolt front is fine for most people.

73-77ish 3\4 ton will be dana 44 front and 14bolt FF.
78ish-87 3\4 ton (78-91 suburban) will be 10 bolt front and either 9.5 14bolt SF or 10.5 14bolt FF rear.
1 ton 4x4's till 87 (or 91 chassis cabs) should be dana 60 front and 14bolt FF rear unless it is a dually pickup then it is common to be a dana 70 FF rear though their have been some that had a wide 14 bolt FF in there.

The "ish" is because the D44 was replaced with 10 bolt front starting in 77 but some 78 trucks still had the D44 so might have been a special order or just using up their stock of a certain ratio. Other oddity about the years will be the front hubs on the K20 axles, 73-76 or so has what they call external hubs that are larger in diameter and look like a 1 ton dana 60 hub. They are thought to be slightly weaker design then the later internal hub D44 or 10 bolt but I wouldnt worry too much on either hub design. Side note is you can take 73+ dana 44 front either a k10 or k20 and swap in over to the later internal hubs by using the spindle\backing plate\wheel hub and brakes from a later D44 OR 10 bolt.

[Submariner616]

And I thought it was complicated! Thanks for all that info. Are the axle widths and leaf spring mounts the same or will I be having to make modifications?

[aotte1]

One other item to consider, is the change in steering linkage geometry from your current front axle/steering linkage, etc., that will occur with a new axle and associated steering components. The steering geometry is different on your 65’ vs newer front axles. Your 65’ K20 ride height is much higher then newer K trucks, thus the linkages are set up differently. Suggest looking at your current steering arm, etc. and compare to newer axle you are considering, to see any differences, along with needed modifications.
Yes the axle alone can bolt in for Dana 44s and 10 bolts. Steering geometry can be an issue.

Will you also, transfer the accumping newer axle sway bar too, likely not a direct bolt on.

On your Qs, newer axles are likely wider, and you would use your old springs for Dana 44s and 10 bolts.

Hope this helps.

Les

[350TacoZilla]

The axles are bit wider but its not really noticeable when you change them out as a pair, especially if you are running stockish tires that dont stick out currently. The front should plop right in, the rear is harder to say because GM did few different pad widths and shock placement but really its all pretty simple stuff to relocate if needed.

This is also one of those projects that can snowball since this is also the time some people go ahead and swap to the newer style suspension at same time to upgrade the springs\bushings.

To add to what aotte1 is saying the steering can either be kept stock style or go to a crossover if wanted but not required. about sway bar I have ran almost all of my stock height trucks with and without the sway bar before and noticed very little difference with my driving style, even my bigger and heavier crew cab diesel I had years ago.

[Submariner616]

Great information. Thanks. So, does any have, or know someone who has, on of the following options suggested by 350TacoZilla:

73-77ish 3\4 ton will be dana 44 front and 14bolt FF.
78ish-87 3\4 ton (78-91 suburban) will be 10 bolt front and either 9.5 14bolt SF or 10.5 14bolt FF rear.
1 ton 4x4's till 87 (or 91 chassis cabs) should be dana 60 front and 14bolt FF rear unless it is a dually pickup then it is common to be a dana 70 FF rear though their have been some that had a wide 14 bolt FF in there.