frame differences

is there any difference in the frames of the 73-87 chevys as far 1/2 ton, 3/4 ton/ and 1 tons? and which frames are truly better the 73-87, 88-98, or the newer ones?  

1/2 ton and 3/4 ton basically had same frames from 67 to 87. GM had some what they called CP6 3/4 ton that had 1 ton frames but the only real difference was in rear and in the "hats" on the C channel were a bit wider. THickness was the same. Starting in 88, GM lightened the frame up a lot on 1/2 tons and they no longer shared frames. Not even the 9.25 IFS fit begin to fit in a 1/2 ton frame without a LOT of cutting and fabbing. Years ago I used to know a guy that used to haul/deliver new trucks to dealers for GM. He told me that when he first started hauling the new 1/2 tons, he racheted them down like he had in the past and when they were unloaded it was found that the frames had bent on most of them.(3/4 tons did not have a problem) They had to devise a new method of securing them to the car hauler deliver trucks.  

i have a 1974(i guess its a 74 it seems to be pieced together it has a front 10 bolt and 14 bolt ff in the back with a sm465 and np205) is there any way to tell if that frame is a CP6? my dad has a 1986 gmc k15 and the frame on it is thinner than on my k20.  

There was no CP6 option in 74. It came out around 79 to boost GVW and get around some emission regs.  

oh ok. that was the reason i bought the truck bc i love chevys and it had such a heavy chassis and drivetrain(exept for the 10 bolt up front)  

The best frame GM ever used in a modern truck back then was 67 to 72. It was a little stouter and frame rails in front were bigger because beginning in 73 that had to notch out the tops of them in front to provide clearance for new emissions style exhaust manifolds.  

well you obviously know more then i do about them lol but iv compared frames and my framje rails are thicker then any half ton from 67 and on but like i said thats why i bought it and with a 14 bolt ff, sm465, np205, good interior with rust free and dent free body for $1300 i couldnt pass it up. i will be looking to box the frame in the future with either tube or 2x4 crossmembers and add to the bottom rear rails to make them the same size as the front and middle sections.(i want to make this a a seriously hd truck lol)  

I have mixed opinions on boxing frames old style frames. Those frame were designed to flex a bit and If I did anything to they I would gusset weaker areas and maybe add some hat sections. Nice thing about C channel is that it has no hidden areas to collect mud, snow and salt and rust inside unseen. Consider this, big HD dump trucks and semi's have C channel frames and there is nothing LD about the frames in those things.  

yes i agree with sno on jus gusseting or boxing in the weaker sections of the frame. n technically i think the frame becomes weaker wen fully boxed i kno it doesnt seem logical but they are made to give. i would box in the rear n front sections for about a foot at both bends for the rear end n maybe weld in a x across the center section.  
'76 k 10 scottsdale

well i dont like to see my frame twisting up like it does and i have heard that in some cases the rivets would start to come out. but i've only heard positive things about boxing the frame like how it makes it stronger and more rigid.  

The problem with boxing is that it increase strain on frame in a lot of areas as flexing does relive stress. Also what a box frame reaches yield point it is weakened and can fail massively. There is more to this than meets the eye. As far as rivets loosening up, you can simply drill them out and replace them with grade 8 bolts and problem will not return.  

i have heard about replacing rivets with bolts and i may do that since it would be alot cheaper and easier then boxing. but i do plan on a roll cage probably just a 4 point in the cab and have a set of roll bars made by auto weld chassis(they have excellent prices as far as i can tell).  

Roll cage is sometimes not a bad idea but then is also raises CG too and increases the odds of a rollover.  

well the only vehicles i have ever drove have had high CG's so i kinda know how to handle them and it wouldnt bother me that much.  

just aquick question i was wondering that since the newer 1/2 tons are lighter duty why arethey rated to tow more than say an older hd? and how much could an older truck tow without having to worry about safety or reliability issues?