XJ body on K5 Blazer frame

[GrimmJeeper]

there are two construction guys out here in socal that had 59 and 62 caddilac limos put on early 70s 4x4 suburban frames, lengthened 4 ft to fit the limo body. they have 500ci caddy motors in em its a blast to watch em playin in the desert down in glamis.

 

[beaterjeepjoe]

Did it happen to look anything like this one?

I can't seem to remember where I found the pic, but just thought it was oddly interesting, so I saved it.

 

[96Yeepster]

After starting this floor pan replacement and finding all kinds of rust in areas I do not want it, like the pinch seam tube... and knowing full well that there is no way in hell I will be replacing all the frame structure in this damned thing...
I would not mind mounting mine on a sold frame.
Fab notched mounts that straddle a 1/4" plate reinforced sub frame and add bushing and bolt 'er down.

 

[GRIMUS99XJ]

Here is a pic that a dude sent me from alaska

 

[Blaine B.]

Hmmm

 

[KSXJ]

Here is a pic that a dude sent me from alaska

Thats one big sled!!! people have way to much time on there hands and no common sense...

 

[GRIMUS99XJ]

Thats one big sled!!! people have way to much time on there hands and no common sense...

X2

 

[outlander]

Don't get me wrong I wouldn't own/wheel it but if its geared right and built halfway decent that thing would be a mud slut!!!
It sure in hell wouldn't make a good trail/rockcrawler....

 

[MaXJohnson]

Why do this?

The XJ body was designed as a unit body assembly - and therefore will be too rigid for a ladder frame (since it's designed to bolster the frame members, while itself being bolstered by them.)

A ladder frame vehicle tends to be a bit more flexible - since the frame and body are separate engineering units, a little "give" at the interface between the two has to be allowed (which is why they use bolts/nuts to connect them - there's just a little "give" there.)

A unit body assembly is designed to be rigidly attached (read: welded) to a frame composed of units of lesser overall strength - since the frame is itself stiffened by the unit body assembly. Removing either from the other makes both considerably weaker - and the "give" designed into a ladder frame would allow an attached unit body to start structural cracking in short order (since the unit body assembly, overall, is designed stiffer than a "box and frame" vehicle.)

Even with considerable engineering going into the attachment of the unit body to the ladder frame (which I doubt happened...) you're still going to get a mismatch - kinda the same effect you'd get using a fire hose to water your rose garden. It will get the job done, but it's not the best way to do it.

Short form - it's mixing two decent things to make one bad thing. Sort of a reverse gestalt - in this case, the whole is less than the sum of the parts.
I could be wrong (it happens a lot... :doh: )
Hope this helps.

no one can pull answers out of their butt better than you.

remove some flimsy rails from the unibody and replace them with the stronger ladder frame and you'll end up with a stiffer assembly. The stiffness of the unibody is definitely not a hindrance; the added weight is (unless you're building a mudder). The separate body and frame are joined with nuts, bolts (and rubber mounts) to isolate NVH, not to accomodate "designed in give". Engineers don't design "give" into ladder frames, their goal is to make the frame as stiff as possible.

 

[bjoehandley]

I believe they did at one time, the thought was that the flexible nature of a truck frame intended to make it work properly in rough terrain, but when the Cherokee and Comanche came out and made that look like questionable logic IIRC. Plus on top of the advantages a stiffer overall body structure the Uni-Body/uni-Frame design brings to the plate, it's also lighter and allowed for a lower CG and greater stability when compaired to trucks like the S-10/15 Blazer/Jimmy, but moreso the Bronco II and Explorer.

 

[5-90]

no one can pull answers out of their butt better than you.

1) I said I was could be wrong (it happens. More often than I'd like, but it happens...)

2) I've said time and again that I'm not a formally-trained engineer - just a mechanic who has decided to try to break into engineering. Most of what I've learned has been by doing and what I've read - and I'm leaner on the theory than I'd like (but I'm working on that.)

Note the second from last line - "I could be wrong." I'll readily admit when I'm wrong - as long as you can prove to me that I am wrong, and tell me how to correct that.

However, I've long been given to understand that a primary advantage of the unibody design was higher torsional stiffness with significant weight savings, that and a few other things I've picked up are what I based my answer upon. If I'm wrong - show me the error of my ways! (Please do - you don't learn from someone telling you you're wrong, unless they show you why they're right.) I am keen to learn...

 

[vetteboy]

Engineers don't design "give" into ladder frames, their goal is to make the frame as stiff as possible.

Respectfully disagree.

As stiff as necessary, as cheaply as possible.

 

[cdhowell]

Maybe it has to do with lift laws, some states measure from the frame. Stacking frames has been done for a long time. Not that its the best idea but a way to get it street legal.

 

[MaXJohnson]

Respectfully disagree.

As stiff as necessary, as cheaply as possible.

Surprising that someone with the handle "vetteboy" would disagree since the evolution of the Corvette chassis is a perfect example. Each rendition of the Corvette chassis has been stiffer than the one before it. This is the primary goal of the hydroformed frame rails. Within the constraints of cost, weight, packaging, manufacturing process, collision energy management, etc. the goal is as stiff as possible. This is necessary to allow suspension components to function as designed and in a predictable manner.If you want to argue semantics, you're on your own.

 

[vetteboy]

Surprising that someone with the handle "vetteboy" would disagree since the evolution of the Corvette chassis is a perfect example. Each rendition of the Corvette chassis has been stiffer than the one before it. This is the primary goal of the hydroformed frame rails. Within the constraints of cost, weight, packaging, manufacturing process, collision energy management, etc. the goal is as stiff as possible. This is necessary to allow suspension components to function as designed and in a predictable manner.If you want to argue semantics, you're on your own.

I was just being a bit of a smartass.

But do you really think that a weak, un-boxed K5 Blazer frame represents the GM engineers' best attempt at stiffness?

I will agree that the Corvette has traditionally been the forefront of GM's design ability. It is a rather semantic argument but I'll still hold to the idea that the frame was only as stiff as necessary to meet the demands of the market in which that car was placed, and evolved over time as the market and its competitors did the same. One of the main reasons I decided not to pursue an engineering job at one of the major auto companies is because the design potential for many things is limited by the market and the accountants, not what's necessarily the best for performance. Irrelevant in this thread though.

5-90's correct in that most of the weight it adds would be low, however most of the folks that attempt this sort of thing end up with a rig much taller than it really has to be, so I guess that kind of balances out.

 

[87manche]

the difference there is that hydroformed vettes are a brand new technology.
He's talking about stuffing an XJ body onto a 20 year old c channel K5 frame.

Half the flex that comes from a K-5 is in the chassis. Ever see one flexed out and then go look at the body mounts? They're screaming for mercy.

 

[XJeremy23]

Did it happen to look anything like this one?

I can't seem to remember where I found the pic, but just thought it was oddly interesting, so I saved it.

It did look similar to that. The one I saw had more streetable tires, mud flaps, and bushwacker fender flares, probably to make it street legal. Interestingly it was the same color as that one it just had chevy and K5 emblems on it. HMM, I wonder if it is the same vehicle with some changes made to it after that photo was taken? Too bad I didn't get a photo of the one I saw.

 

[87manche]

I do like that guys windows sticker though....


You need to understand.

 

[Zifos]

"Each rendition of the Corvette chassis has been stiffer than the one before it. This is the primary goal of the hydroformed frame rails." -maXJohnson

The reason GM is putting so much work into making the Corvette frame stiffer is because they are trying to get the vette to be as stiff as all the uni-body competition. Because it is a fiberglass body a steel frame is necessary. This gives really low center of gravity (light fiberglass body, heavy steel frame)

maXJohnson:
You seem to be into the technical stuff, try doing a torsional stiffness calculation on 4 inch high x 48 inch wide ladder frame and compare it to a 48 in x 48 in sheet metal tube (uni-body). To make it easy just estimate the frame as a 4x48x120 tube and do a cantilever deflection calculation. Now using the same load you chose for the frame, do the same calculation with a 48x48x120 tube (approximation of a cherokee body). See which one deflects more and then find the wall thicknesses needed to make them have equal deflections.

by the way...
I cut the top of my 88 Cherokee and drove it around for quite a while. The doors all opened and closed just fine and I never noticed any flexing of what was left of the body. I eventually put a roll cage in for safety.

 

[BlueCuda]

A K5 needs something attached to it to stiffen it up. A friend of mine used to have one with 33s on it and the chassis would flex so bad sometimes the fan would hit the shroud from the radiator moving to much.