J truck body swap question

[Auburnmark]

I have a chance to pick up a 72 J4000 with good body/sheet metal, but not much else. My 77 J10 frame and drive train are in very good shape.
Does anyone know if the 72 J4000 body would direct swap onto my 77 J10 frame? Both are LWB/manual 4 speed. I know the cabs changed slightly but don't know about the body mounts or whatever else might be a problem. Thanks in advance.

[threepiece]

All four cab mounting locations changed in 1976. The two rear locations changed in "Z" axis (up and down) and the two front mounts changed in both Z and "X" axis (front to back).

[Auburnmark]

Got it

Thanks threepiece.. just what I was looking for.

Next question would be has anyone out there done this and what is involved moving body mounts? Can a DYI'r with a drill and welder make this work... or are we talking major surgery here? This would be my first body swap so any advice appreciated.

[NeverKnowsBest]

ditto

Very intrested in the responses as well as this is what i'm trying to accomplish as well atm, 73 cab / bed onto a 77 j-20 frame. i currently have the 77 frame bare, but might take another week to get the 73 one bare so i can have them side by side. anything to help with pre-emptive planning would be great.

[threepiece]

Although I have never non this, it could be done without, what I would consider too much trouble.

Modifying the frame is the way to go here, it is less work and you will end up with a cleaner job. With both frames visible, take note of a few common features like holes and surfaces. You can use these to measure from. The bottom straight surface of the frames between the front and rear spring mounting is your datum. You can clamp a straight piece of wood or other stock on the bottom surface from one side to the other and position it anywhere you need to measure your Z height. You can then place a square on the piece of wood to measure other axis dimensions. Be sure to check the bottom for dents or weld buggers, these could affect your measurements. Take notes and draw or pictures.

You can cut off the original support structure and transfer it or make new ones. In either case I would create a hole size and metal thickness that will accommodate an off the shelf "RUBBER" insulator of your choice. Search "universal mount" or "vibration insulator" These are, in my opinion much better than the polyurethane "transmitters". That are commonly used.

[TexasJ10]

I put a 73 cab on an 83 frame. The rears bolted up and the front required me to drill two new holes in the cab directly forward of the old ones. The more forward location meant the the holes were right where the cab support channel starts to curve upwards. I took a piece of 14 gauge steel about two and a half inches wide and about 3 inches long and bent the last 1/2" end up at a 90 degree angle so that the edge accommodated the curve of the support channel. I drilled a hole through this new bracket for the hold down bolt to pass. The new bracket was then welded to the cab support channel. This gives you a flat surface for the stock rubber body mount to sit against,like it is on a stock 83. I really didn't notice the up and down difference in the mount locations and the body lines seem to match up fine.

[threepiece]

I failed to insert the word "not" in the first sentence of post number five. I would consider this swap to be "not" too much trouble.

TexasJ10, what you did looks to be a good way to go. I just looked at my 1981 cab that is exposed on a body dolly. I can see the flat area provided by Jeep for the new design. You didn't notice any change in height because the two cabs share the same mounting surface location, it is the frames mounting structure that are different.

I have reconsidered my position. Rolling the cab on its back side would bring the area to a comfortable place to work. Adding structure to the body and adding a hole would be less work than cutting off frame brackets and remounting them.

The thickness and shape of the new structure is important. It looks like the section of hat channel that curves up on the firewall was changed. I might consider swapping that section or a portion of it if they are in good shape.

[Auburnmark]

Great info ..
Sounds like my plan may be a little work but not to bad at all.
Now I just gotta get this 72 purchased at a price I can live with. As of now, the seller is a bit to optimistic with his asking price for a non running truck. I'm going to have to wait him out a bit but I think he will come around. Its been for sale a while now.
It would be nice to be able to register my truck as a 72 and not have to worry about passing smog every two years. Post 75 in this state has to stay bone stock (with a few exceptions) in order to pass visual inspection. It is very limiting if you want to do any kind of performance upgrades on one of these old relics (even if it actually improves the emissions out the tail pipe!). Its a stupid law but.. it is what it is. Thanks again guys.

[threepiece]

I'm confusing myself here. I did word the first sentence in post number five correctly, it does make the point. I did however spell "done" wrong, I spelled it "non".

Another reason to modify the body as opposed to the frame is the load distribution. Jeep moved the front mount forward in 1976 for a reason. I suspect it may have something to do with distributing the weight of the cab, perhaps to reduce stress in some areas. It looks to me like a better design.

[NeverKnowsBest]

apologies for the bad photo's but its something right ?
this is my 1973-j4700 that i will be pulling the cab and box off of. also the transmission, transfere case out of this are currently on the 1977 frame. Pictures are from drivers side. i thought about trying to take some cardboard and cutting it to match the frame to compare from crossmember mounts but not sure i want to spend that much time in the cold atm lol



1977 side view of drivers side (somewhat prepped frame ) also is it normal for a second set of crossmember holes to be there? i notice its not on the 73...



I took very general measurements from the bottom crossmember bolt just for a basic refrence to the outside of the bracket. *note there is a plate welded of the frame which throws measurements off a bit*

[TexasJ10]

Your frame pictures clearly show the movement of the cab mount to a more forward position. The second set of crossmember holes is normal and were used in the rear position for certain combinations of engines, granny's and transfer cases.

[Heep-J4000]

Mark ,
Isn't it easier to swap the id plate on fire wall and sticker in the door pillar?

[Auburnmark]

for sure

Yes it would be much easier for sure. Problem there is that your actually committing a felony doing so. Don't really want to go there. It is legal to swap a frame/body. The sticky part here is what you register it as (the frame or the body). Every state is different in this regard but I figure with an unmolested cab/body no one would even question it. I could be wrong though .