K20 pulling 19k lbs...

[Hunter79764]

I'd be less worried about turning the frame into a taco immediately with 2800 on a 5th hitch, but if you do it very much for very long, things like shock mounts, spring eyes, sway bar mounts, air bags, etc all will take a pounding that they never were meant to take with 2 tons on top while pushing/pulling/stopping 10 tons behind it, not to mention the torsion forces trying to twist it with big block power and low gearing to get it all moving well...

Like they said above, the K20 frame isn't much beefier than a K10, mostly the torsion is a little stiffer iirc. The 1 ton was significantly stronger in bending by being taller C channel, CC 1 ton stronger yet, and I think all of those are probably less stiff than a 2001 2500HD if I had to guess (don't quote me on that, just an offhand swag). If you boxed the frame, ran reinforcing pads on all mounts, swapped 1 ton running gear with sway control etc, and did it without destroying the heat treat of the steel, I'm sure it could handle it. But that would be item #1 and the rest would follow, and still leaves you open for other issues of going overweight, without at least looking into getting a commercial license and putting the truck in an LLC in case things go sideways, literally.

In other news, everything you have talked about would make a great tow pig for something like a travel trailer. Maybe this one becomes the lake house and you look into a smaller one for camping use? Of course it depends on family size etc. I know with my family (5 kids), we had a catch-22 on RV size. Any trailer big enough for the family was going to require a tow vehicle that didn't fit the family. The biggest tow vehicle we could get that fits the family (Excursion or 2500 Suburban) had tow ratings right around the limit for bumper pulls big enough, and add the kids and luggage and we were way over. Drive a second vehicle, and now every trip will start with an angry wife (she doesn't like to drive on road trips). Our solution was a driveable MH, and one with enough capacity to bring the family, the gear, and the extra vehicle behind it comfortably. If you can fir the family in a double cab truck, a more reasonable 5er or bumper pull fits everyone, stays in the comfortable weight ranges, and still keeps you in a reasonable rig for running to town etc.

 

[Frankenchevy]

The rated payload capacity on an '84 K20 is nowhere near 3500-4000lbs. It's a 3/4 ton... that would be an expected bed capacity in the 1500lb range. The rated towing capacity on these things back in the day was like 6,000lbs... maybe. I have carried 3000lbs of stuff in a squarebody bed but it is spread out over the entire bed, like gravel, wood, etc... I have fully rebuilt suspension, drivetrain, and heavy duty rated components and it gets super mushy and sketchy with that kind of weight in the back.

You are talking about putting a constant, dynamic, 2800lb load on two single points of the frame through a 5th wheel mount. A modern 1 ton that is designed for this kind of thing will have a fully boxed frame in that area that is probably 2-3x the strength of even a crew cab squarebody, which is itself about twice as strong as a single cab K20. I wouldn't even be too concerned with the braking part, except to consider if you happen to lose your trailer brakes you will be completely hosed at that kind of trailer weight. There really isn't anything you can do to help that though. You already have the biggest brake package available and they used that same one all the way through the early 2000's on 3/4 and 1-tons.

The price of admission for regularly hauling that kind of weight is going to start at a 1-ton if you don't want it folding in half. The braking and power side of this is the least of your concerns.

This is a very good point, put 3000 lbs in the bed and drive around. That only represents tongue weight; let alone all the other physics involved with a large trailer that will weigh 3x the original rating of the truck. I still think loaded, your tongue weight will be over 3k.

To put it into perspective, I have a CUCV (k30) with a d60/14ff combo. It was 1-1/4ton rated , which is higher than other squares. I’ve since put ORD springs on, but with the springs pictured below I’ve had 20 bales of alfalfa in it, I’ve had a yard of gravel, a unit of lumber, etc. You know it’s back there.

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[Dano500]

@Dano500
Yes sorry I got a kind of cynical in my replies. I should work on that….
But the same message I think applies.
I have had the fortunate experience of being around/repairing, managing the fleet or being behind the wheel of a whole lot of light duty trucks doing work.
Including back when the 80s squares were just going out of production and still fairly “new” trucks.
And what I’ve learned is there would be a LOT that would have to go into a 30-50 year old pickup to turn it into something that would pull a 13’ tall, 8.5’ wide, 40’ long safely, effectively and enjoyably.
Back when that truck was new, a box trailer the size of a 5ver like yours was at a minimum a med duty or even a small class 8 load.
Being in Houston I’ll assume that your intended use is basically near sea level and relatively flat ground. That does make a huge difference when it comes to power and braking. But it’s also hot AF there and keeping a 500-600hp big block cool and together at consistently the upper end of its duty cycle will also be a big challenge. Case in point, even the newest most powerful gasser pickups out now are only in the low 400s for HP. In an era where there are dozens of car models right off the assembly line with 500-800/900 streetable factory warranty horsepower. Why? Heat and duty cycle.
Yes you can build a 4L80 to be pretty dang bulletproof. But again starting with “inferior” components for the task requires infinitely more time and $ to make them say 100% stronger than what they were originally designed for.
Then add brakes, suspension, and yes the frame. The pounding that an estimated 4klb or more pin weight would put on an old truck is something you’d have to experience towing those loads to understand I think.
And once you get all that in line, you still have an old truck with an upright bench seat and few creature comforts by todays standards.
Oh and wheelbase and weight. Not as much of an issue for handling a stinger steered trailer but instead of the trailer being twice as heavy as the tow rig it’s now 3x + as heavy. And the “semi trucks do it” argument doesn’t hold water in this context. There’s 10x more strength and capability built into a 10 wheel semi tractor even though it only weighs as much as 3 squarebodys.
I think it would be awesome to see and done right, almost an engineering marvel. But there’s a long expensive road to how between now and that future.
Also the “$60k for the right truck” argument is also flawed. By that logic it’s like saying, to get out of this apartment I need to spend $1 million on a house.
Suffice it to say I’m in the (much) smaller camper or much newer more capable truck camp.
Cheers
Good discussion. I can imagine building the ultimate square tow rig but I would never attempt it. Simply out of lack of practicality on most all fronts.

Hey, man, thanks for continuing to shed some light for me.

So, talking about the duty cycle.. the 500cid I was talking about earlier hits 550ft lbs by 2k rpm and stays up there well into 4500 rpm. So, with that being said and a good 4l80e and the right gears, it shouldn't shouldn't have to rev so high to maintain speed if it is 550+ torque at 2k rpm, right?

As far as the pin/tongue weight, it isn't 4k+, it is 2.8k, which should be well within payload for the truck, or am I missing something there also?

It has the 14 bolt rear and 8 pack leaf springs and I have no idea of those ratings so as to add auxiliary springs, or air bags, but I think the biggest concern is if there is an adequate brake upgrade, which I haven't seen much in the way of big-ger brakes and sway factor on the highway. IDK

 

[Dano500]

I'd be less worried about turning the frame into a taco immediately with 2800 on a 5th hitch, but if you do it very much for very long, things like shock mounts, spring eyes, sway bar mounts, air bags, etc all will take a pounding that they never were meant to take with 2 tons on top while pushing/pulling/stopping 10 tons behind it, not to mention the torsion forces trying to twist it with big block power and low gearing to get it all moving well...

Like they said above, the K20 frame isn't much beefier than a K10, mostly the torsion is a little stiffer iirc. The 1 ton was significantly stronger in bending by being taller C channel, CC 1 ton stronger yet, and I think all of those are probably less stiff than a 2001 2500HD if I had to guess (don't quote me on that, just an offhand swag). If you boxed the frame, ran reinforcing pads on all mounts, swapped 1 ton running gear with sway control etc, and did it without destroying the heat treat of the steel, I'm sure it could handle it. But that would be item #1 and the rest would follow, and still leaves you open for other issues of going overweight, without at least looking into getting a commercial license and putting the truck in an LLC in case things go sideways, literally.

In other news, everything you have talked about would make a great tow pig for something like a travel trailer. Maybe this one becomes the lake house and you look into a smaller one for camping use? Of course it depends on family size etc. I know with my family (5 kids), we had a catch-22 on RV size. Any trailer big enough for the family was going to require a tow vehicle that didn't fit the family. The biggest tow vehicle we could get that fits the family (Excursion or 2500 Suburban) had tow ratings right around the limit for bumper pulls big enough, and add the kids and luggage and we were way over. Drive a second vehicle, and now every trip will start with an angry wife (she doesn't like to drive on road trips). Our solution was a driveable MH, and one with enough capacity to bring the family, the gear, and the extra vehicle behind it comfortably. If you can fir the family in a double cab truck, a more reasonable 5er or bumper pull fits everyone, stays in the comfortable weight ranges, and still keeps you in a reasonable rig for running to town etc.

Yeah, I'm beginning to think you are correct and I can't find tow/ payload capacity anywhere for this thing, so for some reason, I thought I had read somewhere that based on amount of leaf springs, was a heavier payload, but that info must have been incorrect. You guys know better than me, so thanks for the input.

I'm still going to do the 500 & 4l80e though. lol Going from 175/275 to 400/550 sounds pretty good to me.

Thanks again,
Dan

 

[Grit dog]

Oh hell yeah 400/550 makes that a fun truck!

 

[Grit dog]

So let’s see the truck and the parts you’re working with here!
There’s a guy who put a 455 olds in his old slammed dually on here.

 

[Grit dog]

This is a very good point, put 3000 lbs in the bed and drive around. That only represents tongue weight; let alone all the other physics involved with a large trailer that will weigh 3x the original rating of the truck. I still think loaded, your tongue weight will be over 3k.

To put it into perspective, I have a CUCV (k30) with a d60/14ff combo. It was 1-1/4ton rated , which is higher than other squares. I’ve since put ORD springs on, but with the springs pictured below I’ve had 20 bales of alfalfa in it, I’ve had a yard of gravel, a unit of lumber, etc. You know it’s back there.

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OMG. Jeffrey’s truck rides like an old wagon with 30psi in the back tires and it’s only the heavy 3/4 ton, lol.
Prolly couldn’t even drink a beer in your truck before the new springs without that yard of gravel in the back!

 

[Dano500]

This is a very good point, put 3000 lbs in the bed and drive around. That only represents tongue weight; let alone all the other physics involved with a large trailer that will weigh 3x the original rating of the truck. I still think loaded, your tongue weight will be over 3k.

To put it into perspective, I have a CUCV (k30) with a d60/14ff combo. It was 1-1/4ton rated , which is higher than other squares. I’ve since put ORD springs on, but with the springs pictured below I’ve had 20 bales of alfalfa in it, I’ve had a yard of gravel, a unit of lumber, etc. You know it’s back there.

You must be registered for see images attach

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Those are some serious leaf springs. Yeah, I don't know if tongue weight would be more than what is documented, so you may be right.

 

[bucket]

I've pulled 13-14k with my C20 Suburban a few times and it did just fine. But it's certainly not ideal since there is not the stability needed to avoid a kid in the road or some idiot that pulls out in front of you. I've also pulled 15k+ behind modern trucks with single wheels many many many many... MANY times and, yeah it does ok with the better brakes and stronger frame, but it's just not comforting. The same loads behind a dually truck just feels so much more stable. Especially the '03-'09 C4500-5500 trucks, as they are reliable, drive nice and can pull 30k with no trouble. As far as modern trucks go, they are more like a squarebody than anything else. They were even built as 4x4's (although a bit spendy).

Also, those folks that say they put X amount behind their truck and "can't even feel it" are 100% full of sh¡t. Or just plain aren't observant.

 

[HotWheelsBurban]

I've pulled 13-14k with my C20 Suburban a few times and it did just fine. But it's certainly not ideal since there is not the stability needed to avoid a kid in the road or some idiot that pulls out in front of you. I've also pulled 15k+ behind modern trucks with single wheels many many many many... MANY times and, yeah it does ok with the better brakes and stronger frame, but it's just not comforting. The same loads behind a dually truck just feels so much more stable. Especially the '03-'09 C4500-5500 trucks, as they are reliable, drive nice and can pull 30k with no trouble. As far as modern trucks go, they are more like a squarebody than anything else. They were even built as 4x4's (although a bit spendy).

Also, those folks that say they put X amount behind their truck and "can't even feel it" are 100% full of sh¡t. Or just plain aren't observant.

My truck knows it's there, it just doesn't bother it much till you want to stop! But I have noticed a slight bit more effort is needed to get off the line with the load and trailer, than without it.
My friend's '19 Suburban with a 5.3 is plenty peppy with no load, and he swears it tows his trailer just fine. My seat of the pants feel tells me otherwise though....it does it, but his '08 with a 6.0 did it better.

 

[Dano500]

So let’s see the truck and the parts you’re working with here!
There’s a guy who put a 455 olds in his old slammed dually on here.

I'm still working on getting the truck running. lol BUT, I have the 500cid already from a 71 cadillac, and still shopping for 4l80e. I'll take some pics once I get it home.

 

[Dano500]

So let’s see the truck and the parts you’re working with here!
There’s a guy who put a 455 olds in his old slammed dually on here.

This is all I have on my phone. lol I took it when I was trying to get info on springs/ brakes. Does 8 springs mean the camper package? lol

 

[Frankenchevy]

This is all I have on my phone. lol I took it when I was trying to get info on springs/ brakes. Does 8 springs mean the camper package? lol

I’m not sure if it was whoever installed the lift block, but they inverted square U bolts when doing a flip kit. I’d look really good at that whole situation back there.

 

[Dano500]

I’m not sure if it was whoever installed the lift block, but they inverted square U bolts when doing a flip kit. I’d look really good at that whole situation back there.

I wouldn't even have known. Thanks for letting me know.

 

[Grit dog]

Factory C6P K20 from the 80s is 8 leaf’s plus the overload. 9 total.
Agree, no bueno on the square bolt, round axle scenario.