Frame Swap: k1500 4.3l -> k2500 Frame

strikk · Nov 14, 2017

Do I dare ask this question..

My trusty '98 4.3l k1500's frame is on its way out. Back in 2014/2015 I had put a reman'd 4.3l motor in it. It is currently at about 25k miles and running minty fresh. The frame on this truck was repaired last year some time but it was only considered a temporary to get me through a winter or two.

Now I've got a lead on a 97' k2500 8600 gvw rolling frame that I will absolutely be purchasing for one use or another or even to resell. Would it be a waste of my time to swap over the 4.3l motor/trans cab and body on to this k2500 frame? ~~k2500 RCLB were offered with the 4.3l so I'm expecting things to match up pretty well~~ but of course I don't know what I don't know.

I will for sure need to get better information on the axels and transfer case of this new frame but at the end of the day what kind of compatibility is there with the outputs on the transmission to transfer cases of these two configuration (k1500->k2500)?

BowtieBrody · Nov 14, 2017

I've never seen or heard of an 8600 GVW, or even a 7200 GVW C/K2500 being optioned with a 4.3; body panel wise for the front clip, cab, and bed all the mounting points should match up.
What engine did the 8600 chassis have in it originally?

strikk · Nov 14, 2017

I am 100% mistaken on the k2500 being optioned with a 4.3l according to our vehicle dimension sticky: http://www.gmt400.com/threads/gmt400-vehicle-dimensions.13725/ and the GM 'up fitter' manual the only trucks with 4.3l optioned from factory are indeed c/k1500 models only

From my very limited understanding cabs are cabs. motor mounts are motor mounts, is it sufficient to think thats more than half the battle?

skylark · Nov 15, 2017

Actually, I had a 91 sclb light duty 4.3/700r4/3.42 C2500. It also had a 14 bold semi float rear end. It was an ex school district truck. I've purchased several ex fleet vehicles over the years and the always seem to have weird options. Either way you will have to swap the frame side engine mounts for the 4.3. The V8 used a different mount.

gstubbz · Nov 15, 2017

From what I've heard you could get a "light duty" 2500 with a 4.3 and a GVWR of 7200, but a truck with a GVWR of 6600 GM classified as a half ton. My 94 K1500 with a 6.5 and factory Z71 package was rated at 6600 (so half ton) when most of those lower class 6.5 trucks were badged as a 2500. Some grey area exists, my friend just purchased a 91 K1500 ECSB with a 4.3/5spd that has a factory 14b semi float rear axle and a 6600 GVWR.

Anyway, to answer your question, yes you can put your K1500 stuff on the K2500 frame. I would just reuse the actual 8 lug axle that was under that new frame you are buying.

You can reuse your driveshaft although you will more than likely need a 447 or 448 conversion U-Joint for the rear axle if you decide to go with an 8 lug axle.

Transfer cases between both trucks will be a NP241 unless for whatever reason your truck was optioned with electronic shifters, in which case you'll have a NP243. You should be okay to reuse your front driveshaft for the diff.

Like mentioned above you will need to swap engine mounts on the k2500 frame to fit the V6.

Output shafts:
4L60e - 27 spline
4L80e - 32 spline
NV3500 - 32 spline
NV4500 - 32 spline

So basically, if your truck is a 5 speed it will have the bigger output shaft already. If it's a 4L60e you'll need to swap slip yokes with a conversion u joint. I don't know exactly what you want to use and mix and match between both k15/k2500 trucks so there is a rough idea.

strikk · Nov 16, 2017

I love the information guys, thank you very much!

I'll be keeping the 8 lug drive train, no reason not to in my eyes. I'm currently running the 4l60e on the original truck with floor shift np241. I'll have to find a drive shaft as the original truck is a short box and the new truck is a long bed. I will look further into the conversion u joint in the rear.

I am getting super excited to finally have a solid base for my truck, living in the northeast the current frame im using has already been cut in half once and i'm looking forward to finally replacing it to have a solid platform going forward

jdla140 · Nov 18, 2017

gstubbz said:
From what I've heard you could get a "light duty" 2500 with a 4.3 and a GVWR of 7200, but a truck with a GVWR of 6600 GM classified as a half ton. My 94 K1500 with a 6.5 and factory Z71 package was rated at 6600 (so half ton) when most of those lower class 6.5 trucks were badged as a 2500. Some grey area exists, my friend just purchased a 91 K1500 ECSB with a 4.3/5spd that has a factory 14b semi float rear axle and a 6600 GVWR.

Anyway, to answer your question, yes you can put your K1500 stuff on the K2500 frame. I would just reuse the actual 8 lug axle that was under that new frame you are buying.

You can reuse your driveshaft although you will more than likely need a 447 or 448 conversion U-Joint for the rear axle if you decide to go with an 8 lug axle.

Transfer cases between both trucks will be a NP241 unless for whatever reason your truck was optioned with electronic shifters, in which case you'll have a NP243. You should be okay to reuse your front driveshaft for the diff.

Like mentioned above you will need to swap engine mounts on the k2500 frame to fit the V6.

Output shafts:
4L60e - 27 spline
4L80e - 32 spline
NV3500 - 32 spline
NV4500 - 32 spline

So basically, if your truck is a 5 speed it will have the bigger output shaft already. If it's a 4L60e you'll need to swap slip yokes with a conversion u joint. I don't know exactly what you want to use and mix and match between both k15/k2500 trucks so there is a rough idea.

6600 GVWR trucks are just a 1500 with the heavy duty chassis option, RPO code F44. It could be had on any 1500, and it always included a 14b semi floater except on some very early trucks. I believe all diesel 1500srequired the option, both of my trucks have it. 7200 GVWR is a light 2500, which is very similar to the "f44 1500". From what I've read, if it had 6 lugs a 4.3 was available.

williebee · Nov 20, 2017

The 4.3 engine is actually a 5.7 engine that has been cast with only 6 Cylinders.
The internal components (pistons, rods valve train) are all the same parts.
All of the accessories on the front of the motor will bolt up to either block.
That being said, The motor mounts that worked for a 5.0 or a 5.7 will work with your 4.3.
I did an engine swap on an older model S/10 truck from a 4.3 to a 5.7 and it was virtually plug and play except for the space between the motor and the radiator.
Hope this helps

skylark · Nov 20, 2017

williebee said:
That being said, The motor mounts that worked for a 5.0 or a 5.7 will work with your 4.3.

This definitely isn't the case with a 400. You absolutely have to change the frame side mount when going from a V6 to a V8.

strikk · Nov 20, 2017

I went and picked up the frame with a little bit of a surprise. Originally the deal was for a rolling chassis but the seller didn't spend the time to pull the motor/trans/tcase. The final deal ended up being $500.

'97 ECLB k2500
14 bolt, 4.10 gears
5.7l, 4l80e
Floor shift tcase
Engine harness and ECU are all in place

It's in great shape for anything I can find in the northeastern, New England area. It is missing the rear cross member and could use a new rear gas tank cross member but I consider that an easy fix!

I will begin pulling it apart over the next few months as time permits and hope to have it all blasted and painted by spring time!

I am super excited! I can't wait to get some updates on my build thread!

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Frame Swap: k1500 4.3l -> k2500 Frame

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