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Rear Frame Crossmember Replacement

by Jeff Heidman
 

Jeff is restoring a 1953 CJ-3B as an M606 military Jeep, and in 2011 he was restoring a replacement frame. He described his project and got some input from the CJ-3B Bulletin Board and the Willys Military Jeeps Forum.
 

FrameJeff: "Two years ago I picked up this prize and needed to replace the crossmember (150K JPEG). I found Midwest Military had the best kit for a replacement crossmember. This is a replacement M38 not a CJ-3B crossmember, but with my intentions of adding bumperettes and a pintle for my M-606 conversion it works great! It was $115 from Midwest Military and comes with rivets as a kit. It is beefier than stock. Keep in mind the only difference between a CJ-3B bumper and M38 is the bumperette holes and lack of licence plate bolt slots."
 

Rivets"I drilled/chiseled off the heads of the rivets, and cut the small factory welds to be able to "free" the monster. I test fitted the MWM parts and found they fit great. The replacement rivets were 3/8" diameter but the holes are 7/16" I thought I needed to get larger rivets but they smashed and filled up the holes when I shot them."

Wes on the Willys Military Jeeps Forum said, "This discrepency has been addressed in the past and has been explained as a manufacturer's deliberate attempt to make the crossmember easier to fit with many frames that may not be in perfect alignment."

John of MWM clarified: "The holes in the crossmember were measured from an original M38A1 part. The hole diameter is not supposed to be the same size. They compensated for the expansion of the rivet to take care of this. We have recently dissected an 1952 M38 and the holes on that crossmember match the one we made."
 

Jeff: "Here's a few pics of what the rivets looked like."

Prep"I used a friend's torch and a rivet gun and set from work, to "buck" the steel rivets. It worked great. I used a rust inhibitor spray called 'The Must for Rust' to treat the parts before assembly and painting. I have since painted the frame with "Zero Rust" paint to keep it from rusting, and shot it with a coat of rustoeluem gloss black. It has been hanging under my deck ready for service when I get ready to swap it over.
 

Nick commented: "I just cut the rear crossmember out of my frame yeserday. I cut all of the rivet heads off and popped the rest out with a puch. Unfortunately, mine was badly mangled when I backed up over a tall stump at a steep grade and became stuck between the diff cover and the cross member. It's not a good predicament to be stuck in and the crossmember proved to be inadequate in that place at that time. I'm going to upgrade to something beefier. Yours looks very good."

Prep

Rus Curtis added: "Nice work. I do feel obligated to point out a few things that may be specific to the differences between the M38 and CJ-3B on this. You've already pointed out the extra holes but it goes a bit deeper than that. I'm glad that, as you carefully disassembled the rear cross member, you not only took pictures but also preserved the pieces.

"You will note that there is a brace that fits inside the rear cross member. I believe that part to be identified in the Parts Manual as:

Group 35-04 - DRAW BAR
804131 1 Reinforcement, frame cross member, rear.
 

"I notice a difference in the outer edge of this reinforcement member between the two (original and replacement) that specifically will alter the attachment of that piece.

"Note your picture of where the original draw bar had been detached and the rivet heads cut off. You can see that the vertical attachment of the drawbar bolted directly through both pieces. Additionally, from the inside, you can see that reinforcement was attached to the frame "C" channels as well - on the bottom using a bolt. I also noted on mine that there was a center bolt attachment on the bottom too. I can see the remains of that hole on your original but it seems to be missing on your replacement.

"Are these differences a problem? I don't know. These differences may be due to the location of the pintle attachment (and how loads would be registered and dissipated) and the fact that there should be bumperettes on the M38. Those bumperettes may provide the additional bracing needed.

"I would only advise anyone looking to use this excellent kit to either plan on altering the inner reinforcement or shopping around to compare other kits for differences. Otherwise, using a standard draw bar may (emphasis on may) put unnecessary stress on the rear cross member if towing or pulling. That outer draw bar attachment, in my opinion, will need the additional bracing.

"When I did that part of my rebuild, I ordered a rear cross member (that came without the reinforcement) and took the pieces to a machine shop and had one made."

PrepJeff replied: "Not pictured are two additional 3/16" plates that bolt on both the rear crossmember and the drawbar plate to secure both together; it's just in the garage attached to the future pintle hitch to prevent loss. Thanks for pointing that out.

"And yes, the doubler is different on the ends and will need to be welded to the frame on the ends to strengthen it. I still have it hanging under my patio deck waiting for installation."

Rus Curtis: "Yes! Look at your old insert to see how it ties into the frame. I suspect all those contact points via nut/bolt attachement gave the rear frame crossmember the needed rigidity to make pulling a load safer."
 

Tools

Bob: "I'd be curious to know how you got in there with a tool to swedge those rivets down so nice! And what kind of tool you used."

Jeff: "I used a rivet gun (aircraft) and a bucking bar that I used to use during airframe overhauls. Shot the rivets with the help of a friend's torch and a rivet gun with a flush set and a heavy bucking bar (one of the perks of aircraft maint.) I used the rivets included with the crossmember -- I didn't think they were the right size for the hole size drilled in the crossmember, but they turned out fine."

Rivet gunWes: "This is the riveting pneumatic gun. You'll need at least a 4X or larger gun.
 

Rivet set"The flush rivet set is placed in the gun and used to strike the front of the rivet.
 

Bucking bars"These bucking bars are used to get into those tight places. They would be placed against the back end of the rivet that will mushroom out. Links for tools: Brown Aviaiton Tool and Aircraft Tool Supply.

"I am an aircraft mechanic and use these tools very often. In fact a lot over the past 45 years. We seldom used more than a 3X gun and rarely have to heat or use steel rivets. Howver when you start talking 3/8" steel rivets and 5X or 6X gun and a torch you must heat these rivets cherry red to set them adequately."
 

Bucking barJeff: "I used this bar for the upper and lower rivets. For the rear facing rivets I used a flat bar clamped to hold the rivet head against the frame, and shot the tail of the rivet with the flush set. Could have been done the other way."

Wes: "An extra set of hands is always a good idea. Especially with the large bore 4X and bigger rivet guns. It can be quite difficult to keep the flush rivet set where you want it and work the bucking bar on the other side of the rivet by yourself. If that rivet gun walks, you will get some serious deep sharp dents on the adjacent steel."
 

Other Options

A 2006 discussion on the CJ-3B Bulletin Board raised a few other questions and answers.

Classic EnterprisesEd Wilson had a problem: "I ripped the rear crossmember (bumper) in half yesterday, right next to the pintle hitch. You can do this with a military trailer full of wood when it jackknifes on an old mountain logging road. I would appreciate any tips on replacing this piece, or sourcing a quality replacement. I haven't looked yet, but I would think it is a fairly straightforward procedure."

Meanwhile, Walt Snelling was thinking about restoring his bumpers to original condition: "My 1954 CJ-3B has a steel reinforcement inside the rear bumper sheet metal. The holes and how it is attached all seem original. This Jeep had the standard drawbar. My 1955 CJ-3B does not have this reinforcement, but was a Navy Jeep with a pintle hook. My question is, was this reinforcement just used with the drawbar, or is the Navy Jeep missing the reinforcement? Secondly, if one elects to replace either the front bumper or rear bumper, what is the best way to replace the rivets that hold both items to the frame? My bumpers are not perfect, but they are good enough that I would not want to use a replacement bumper if that meant bolts in place of rivets."
 

RivetingRight: Frank Porfidio rivets with a "heat wrench" (torch).

Buck Toenges: "My two CJ-3Bs both have an inside channel rear crossmember that is riveted between the frame. I think that this inside rear crossmember is welded to the outside rear crossmember. Classic Enterprises makes a repro inside crossmember."

Bob Christy: "This thing is a two-piece deal, one inside, one outside. I think all CJ-3Bs had the inner reinforcement on the back bumper. The bumper is tack welded to the frame and another flange from the 'A' frame is welded to it also. I don't think the inner bumper was welded at all, but it's hard to tell as mine was pretty much gone. I would definitely get something in there to prohibit rust.

"I ordered one from Classic. The thing looks nice but still needed a few holes drilled in the right places. I used stainless steel caphead screws to put it back on. Don't do like I did and put it on centered to the frame. It looks right, but it's not. It is supposed to stick out on thedriver's side more than on the passenger's. I don't know why this is, but I had to take mine off and start over. I paid $85 for it. I think if I were not out for the original look, I would just make one... it'd be stronger."

Leslie Moore suggests another source: "There's a guy in Branford, Connecticut who makes an exact replacement. He owns Brian's 4WD Parts, phone 203-481-5873."
 

Hubbard's Halfcabs: "The right side is shorter to get the tailpipe up and out of the way.

"Sounds like a lot of pressure on that pintle. Not so much weight, but the leverage from the jackknife must have done the damage. Can you open your tailgate with the pintle in that position?

HH's bumper"The standard OEM straps (from the drawbar) usually only have the top four holes drilled. On mine if I had used those top four I wouldn't have been able to open the tailgate without ramming it into the top of the pintle hook, so I drilled 2 more holes in the straps to correspond with the holes in the rear cross member (bumper). I put the two safety chain eyelets in the top 2 holes and the pintle in the bottom four holes.

"This setup in one way is stronger, in that the force through the pintle is taken by the rear cross member and the v-brace. With the pintle in the upper position the full force is taken by the v-brace and only indirectly by the rear cross member, since the v-brace is usually welded to the rear cross member (bumper) and has a plate welded in there to tie them both together.

"My trailer is level due to the addition of the add-a-leafs in my Jeep spring packs -- i.e. the Jeep sat up higher."
 

Haley frameAlan Haley: "I had to replace the crossmember when I rebuilt my 3B as it had rotted out completely. I used a piece of channel iron. I believe it was 6-inch but in any event it has to be slightly larger than the original crossmember as there is a slight radius in the inside of the channel and you want to be able to bolt it up flat against the frame. To get the recess in the middle I cut a slice out of the channel that was 1/8 inch larger then the contour on the original piece. I then welded a piece of 1/8-inch strap iron that was as wide as the thickness of the channel to one end of the cut, heated the strap and pounded the first few inches into the cut channel and welded it there. I then heated a few more inches and welded and continued with this process, until I got to the end of the cut that I had made in the channel.

"After the process was done I ground the welds down and rewelded any places that I screwed up. I clamped the piece up to the frame and bored holes, using the original bolt holes in the frame as a guide. I am not much of a metal fabricator or welder but I was amazed at how well the piece came out. It took me about 2 hours to do the whole thing. I can also guarantee that no jackknifed trailer will break this cross member in half. Of course you may prefer that to ripping out your whole rear end because of an overbuilt crossmember."
 

Ed Wilson: "I went to the local machine shop with the pieces of the old crossmember and measurements. We determined standard 4" channel would work. They duplicated the cross member, right down to the elongated license plate holes for $100. I have done much the same thing as HH describes with the two extra holes in the pair of center straps, except I am simply bolting the two straps to the new cross member for added strength.

"I primed and painted the new piece and the drawbar assembly, and the installation was fairly straightforward. I used grade 8 bolts in all assembly. I am confident the 4" channel is stronger than the original at near the same price. I have a new respect for the trailer and a much stronger 'hard point' for the hitch. At 10 feet you can't tell it from original, and all the other components are intact should I want a full resto in the future. The tailgate is bolted through the chain eyes for... uh... structural integrity, so opening the tailgate is not a factor for me."


Thanks to Jeff Heidman, Ed Wilson and the other contributors. -- Derek Redmond


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Last updated 30 November 2015 by Derek Redmond redmond@cj3b.info
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