Question on Major Differences

[SourTooth307]

So, aside from the number of wheel lugs, what are the major differences between a K/10 and a K/20? Advantages? Disadvantages? I wanna know what/if I'm missing out on anything......

[Keith Seymore]

K20 has
Heavier duty frame
Bigger brakes
Heavier duty suspension
Bigger wheels and tires
Higher payload rating

[andrewmp6]

K10 could be long bed or short bed k20 was long bed only.It depends how you want to use the truck.A off road toy i would go k10 short bed,As more of a work truck/tow pig k20 or k30 depending what you need to pull/haul with it.

[SourTooth307]

My K/10 is pretty much an off-roader and generic pick up whenever I need one. Is there anything from the K/20 that is popular to carry over as sort of an off-roading advantage?

[kevinr1970]

Originally Posted by Keith Seymore

K20 has
Heavier duty frame

I have read/heard different things on this; c-k/10-20 used the same frame, c-k/30 went to a heavier frame.
I have also heard that 10/20 frames were dimensionally the same, but that the 20 used thicker material.
Another one is that certain 20's used heavier gauge frames (or was the same as the 30's?), like an HD version vs. a standard version?

Yo', what is really goin' on?!?

[andrewmp6]

The k10 and k20 used the same front axle besides the lug pattern.The rear axle can be a 14 bolt but you want a full float don't waste your time on a semi float.Besides that most of the parts are the same thing you have on your truck now.If your looking for upgrades then k30 is what you want to look for.The k30 had a dana 60 front the rear will be a full float 14 bolt or a dana 70 i think if its a dually.And the k30 used the np205 t case you could swap it in your truck with a adapter kit.

[Keith Seymore]

Originally Posted by kevinr1970

I have read/heard different things on this; c-k/10-20 used the same frame, c-k/30 went to a heavier frame.
I have also heard that 10/20 frames were dimensionally the same, but that the 20 used thicker material.
Another one is that certain 20's used heavier gauge frames (or was the same as the 30's?), like an HD version vs. a standard version?

Yo', what is really goin' on?!?

I hear that a lot.

Here's the Frame Specification chart from a random generic info packet from the GM Heritage Center archive. (I happened to choose the 1979 model year).

You can readily see the differences between a C10903 and C20903, so it is not possible for them to be the same.

The K10903 and K20903 have the same section and modulus criteria so it is possible. I did look up the part number in the engineering release and there are different part numbers shown, so there is some physical difference between the two (but I can't tell you how significant it might or might not be).

There was no 2500HD like there is today. Back then a 10 was a 10 (...other than a "heavy half"...), a 20 was a 20 and a 30 was a 30 series.

K

[kevinr1970]

So looking at the PDF from the GM Heritage Center archive for model year 1985, for a regular cab it lists different section modulus from a C20/2500 vs. a C20/2500/C6P (3.57 vs. 4.53).
And a similar difference on the K10/1500, K20/2500 vs. K20/2500/C6P (3.88 vs. 4.53).
All of which is less that the C/K30/3500 (6.14).

Is it possible that in '79 there was no HD 20 series truck, but here was in '85 (C6P)? I goggled GM C6P and it brings up a lot of chatter about a heavier duty version of a 20 series truck, maybe a precursor to the HD trucks? They all seem to mention SF vs. FF rear, heavier spring packs, etc. I didn't see any mention of a frame difference. But this was almost all about the '88-98 body trucks.

Bottom line(??) on the frames is C10's frame unique, C20 unique, K10/K20 share frame, and a C6P version being unique for both C and K?
Or something close to that?!?

Originally Posted by Keith Seymore

I hear that a lot.

Here's the Frame Specification chart from a random generic info packet from the GM Heritage Center archive. (I happened to choose the 1979 model year).

You can readily see the differences between a C10903 and C20903, so it is not possible for them to be the same.

The K10903 and K20903 have the same section and modulus criteria so it is possible. I did look up the part number in the engineering release and there are different part numbers shown, so there is some physical difference between the two (but I can't tell you how significant it might or might not be).

There was no 2500HD like there is today. Back then a 10 was a 10 (...other than a "heavy half"...), a 20 was a 20 and a 30 was a 30 series.

K

[whiskeydented]

andrewmp6, some 1/2 ton and 3/4 ton trucks came with 205s.

[andrewmp6]

Yeah the np205 came in some 1/2 and 3/4 ton but most was used on a stick and not as easy to find as one from a 1 ton.If you want a list http://www.chuckschevytruckpages.com/73-87specs.html

[donut]

andrewmp6, the np 205 was standard on the older K-20's (maybe even the 1/2's). If you wanted auto and 4wd, you got the tbh 350/ np 205 combo, iirc the turbo 400 was not an option till later years (much like a big block) Spline counts are different on the transmissions, so you can't easily do a mix and match. I think the 465 was 10 spline, the turbo 350-27, turbo 400-32

[cadillac_al]

You're not missing out on much. I used to drive a K20 and now I drive a K10 and I like my highway friendly 3.08's. The only time I would miss the K20 is towing a large vehicle and mud bogging. I retired from mud bogging but my mostly stock K20 brought home a lot of trophies. The K10 is doing everything I need now and the K20 would be overkill for my light duty work.

[Keith Seymore]

Originally Posted by kevinr1970

So looking at the PDF from the GM Heritage Center archive for model year 1985, for a regular cab it lists different section modulus from a C20/2500 vs. a C20/2500/C6P (3.57 vs. 4.53).
And a similar difference on the K10/1500, K20/2500 vs. K20/2500/C6P (3.88 vs. 4.53).
All of which is less that the C/K30/3500 (6.14).

Is it possible that in '79 there was no HD 20 series truck, but here was in '85 (C6P)? I goggled GM C6P and it brings up a lot of chatter about a heavier duty version of a 20 series truck, maybe a precursor to the HD trucks? They all seem to mention SF vs. FF rear, heavier spring packs, etc. I didn't see any mention of a frame difference. But this was almost all about the '88-98 body trucks.

Bottom line(??) on the frames is C10's frame unique, C20 unique, K10/K20 share frame, and a C6P version being unique for both C and K?
Or something close to that?!?

I suppose you could look at it that way but C6P just designates the 8600 lb GVW.

The two typical (historic) GVW ratings within the 3/4 ton models were 7200 lbs and 8600 lbs.

If we had developed a "2500HD" back then I would have pushed for more than the typical 8600 lbs GVW.

K

[andrewmp6]

Donut the np203 and np205 look a like and people mix them up,On the older trucks more came with a np203 then a np205,Check the link i posted that will give you the break down of what came in what years.

[kevinr1970]

What exactly does "section modulus" refer to or mean?
If it is different on the C/K20's for the C6P, doesn't that mean that the frame is different/stronger? The page you posted from the manual for the '79 lists the frame thickness, but it didn't for the '85 I looked at. At least not anywhere near where the spec's I was looking were.

Thanks for taking the time to answer these questions!

Originally Posted by Keith Seymore

I suppose you could look at it that way but C6P just designates the 8600 lb GVW.

The two typical (historic) GVW ratings within the 3/4 ton models were 7200 lbs and 8600 lbs.

If we had developed a "2500HD" back then I would have pushed for more than the typical 8600 lbs GVW.

K

[Keith Seymore]

Originally Posted by kevinr1970

What exactly does "section modulus" refer to or mean?
If it is different on the C/K20's for the C6P, doesn't that mean that the frame is different/stronger? The page you posted from the manual for the '79 lists the frame thickness, but it didn't for the '85 I looked at. At least not anywhere near where the spec's I was looking were.

Thanks for taking the time to answer these questions!

"Modulus" is shorthand for "Modulus of Elasticity" - or a generic measure of how "rubbery/bendable" the raw material is.

"Section Modulus" takes that measure of the raw material and adds the effects of the geometry, specifically the vertical section of the rail and the width of the top and bottom flange, to define the frame stiffness as designed.

A higher number means more stiffness.

K

[donut]

Originally Posted by andrewmp6

Donut the np203 and np205 look a like and people mix them up,On the older trucks more came with a np203 then a np205,Check the link i posted that will give you the break down of what came in what years.

Thanks for the correction. I knew my '73 the 205 was standard and thought that didn't change until '75. my bad. I do know the junkyards I hit had many more 27 spline units than the more popular turbo 400 models.

Hence the reason the old K-20 stayed with the turbo 350 instead of the turbo 400 I had in the shed.

[andrewmp6]

The reason a 32 spline is harder to find is all the doubler kits 205/203 use those.You can change one over its about 135 bucks but if your going to open the case might as well rebuild it.