Extending rear of frame on 72 CJ5???

Hi All,
I searched on this topic and found alot of info. That only led to more questions. I am considering extending my rear frame and adding 8" or so to the body of my CJ5. This will gain me the needed driver's seat room and also allow me to extend my wheelbase a bit. Extending the body is easy and for the frame I intend to use 2x4x3/16 wall. My questions are regarding what to do where the 2x4 and the original frame meet. I am expecting that I would need to sleeve the original frame with the 2x4 but what happens at that point where it meets. When welded will it create a point of failure for the chassis? Meaning the original frame flexes alot and now it is going to have a more rigid area of 2x4 frame. Is this going to cause the original frame to crack at that point? Will I need to box the whole length of the frame to make it as stiff as the new 2x4 section? Any suggestions?

Again I read all the posts I could find but didn't see a specific answer. I saw a few posts where it was said that boxing the frame around the spring mounts causes failure at that point so I am assuming this would be the same but wanted to check it out.

Mike

 

Not an expert on this, but here's my understanding. Most of the stress on the frame is on the top and bottom rails, with the top rail in compression (usually) and the bottom rail in tension (usually). Welding across the rail, perpendicualr to the frame, is bad. The strongest weld is along the length of the frame, so that tension and compression are parallel to the weld rather than perpendicular to it.

One example of this is the strap along the bottom of the frame of a CJ-6, where it is in tension, and is stitch welded along its length. I believe the ends of the strap are not welded.

Welds used for repair of the web of the frame (vertical part) are often cut with a long V, called a fish-mouth, that make the normally vertical welds more horizontal. The same principal could be applied to the welds joining the rails together, but I think it would be more advisable to join them with a strap or similar shape with welds only running parallel to the frame.

 

Another suggestion - instead of using 2x4 tube, why not recycle parts of another frame? That is, make the extension of similar material to the original frame. The CJ-6 frame is the same as the CJ-5 frame except for the strapping. Wouldn't even have to be a Jeep frame - just a frame with similar cross-section.

 

i have streched many semi trucks,now i no that they arent the same but the big truck fame has to flex alot also.i always used frame rails from a donor truck to do the job and dont just cut it of from top to bottom cut down the frame in an angle. and then you will need no sleeve.it will be strong as new.just my nickles worth.,jared

 

I have been doing some more research on how to best attach the new rear pieces to the existing frame. Searching the PBB turned up the following piece that was done for extending a TJ frame. Looks like the welds would spread the stress out in a diagonal instead of a vertical. This would seem to be a better solution with less chance of a stress crack forming from frame flex. Make sense?

Timgr and Jcarson----I don't know of any frames or parts rigs kicking around so getting a piece of CJ frame to extend it with might not be as easy as just picking up the 2x4. Thanks for the suggestions.

 

I would build a new frame from the 2x4 box. The original frame is c-channel, and I don't think that the box-to-c joint would be worth the risk. I guess it also has to do with how big of tires and what motor you want to run.

Might be easier to cut the frame, add a crossmember and build a 4-link. Similiar to this:
http://www.rockymountainextreme.com/showpost.php?p=100155&postcount=24

 

For insight, I would get on the internet & search the frame rail sectioning technique for frame rails on a unibody construction auto and or frame end sections on a full frame truck or SUV. They are remarkably similar to the photo you posted & most have been crash tested to prove strength & durability. They crash the cars, do the repair & crash 'em AGAIN to see how it worked. Then they send the tested results out to body shops & insurance company employees to insure proper/correct technique. Tech-Cor (Chicago, IL) is a company owned by a MAJOR insurance company that does a lot of this type of testing...There maybe something there on line to guide you.

 

Thanks for the replies guys. I am hoping to start on this soon. I cut the body and extended it 12" last night. So once that is finished I'll be starting the chassis. I'll do some searching on unibody frame sectioning.

Mike

 

just got done streching my cj5 20 inches,we used round tube. 2 1.5 inch tubes fit the frame rail perfect.went to full width truck axles and leaf springs.new wheelbase is 103"


dave

 

Got any pictures? I think I have seen some pics on the net somewhere of extending a toyota frame that way or maybe it was a TJ.

Mike

 

i will shoot some pics and try to post them

dave

 

Thanks! You can send them to me if you have problems posting them.

Mike

 

mike here are some pictures sorry for the delay took me a while to figure out.
dave

 

Dude! that's just plain cool!. Way good job on it.

 

Thanks for the pictures General. That looks really good.

mike

 

hey guys im gonna do the same thin to my 52. extend,full width,sm465 and a 205 case i just blew the tranny out i figured i would i got about 350 hp lol. i got an old farm truck with a bad engine dad give it to the neighbor boy i had to buy it back buttttt,its got a 60 front:twisted: . i just wonder if i could get some pics of the genralsjeep and jeepdriver if you got yours done think i could see it thanks alot,jared

 

Jared,
I have posted all the pics of the stretch in this post. My signature also has my website info with more pics. Hope they help.

http://www.earlycj5.com/forums/showthread.php?t=20438&page=6

Mike