Jeep TJ Rear Bumper Project

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Patterned after the Bulletproof rear swing out tire carrier bumper, our rear bumper project is not as hard as it appears as long as you have some good metal fabrication skills and tools.  At a bare minimum you will need a good welder, 1/2" drill (a drill press is even better).  A small 4" or 4.5" hand grinder is a must for cleaning up the welds.  You also need a way to cut metal such as a bandsaw or cut off saw.  You might find it easier to get all your metal pre-cut at your metal supplier.  Most shops charge $1.00 per cut and it can be well worth it if you have limited cutting ability.

Mounting bolts & tabs

We start with a 3" x 4" x .188 steel tube cut at 56" in length for the body of the bumper.   We first bevel cut each end.  Most of the time we choose to just cut a 45 degree angle on each end however you can do just about anything you want.  Once the bevel cuts are made the tube is marked at the center point.   We also make a mark at the center point of the rear cross member on the Jeep.  Aligning the two marks the tube is then clamped to the cross member and we make sure that the top of the tube is flush with the top of the cross member.  A Sharpie marker is then used to mark the location of the original bumper mounting holes on the back of the bumper tube.   Make sure to double check the marks you made and take some good measurements to insure that you have them in the right position. When you are satisfied, remove the bumper tube from the Jeep, use a center punch for each hole and then drill the 4 - 1/2" holes for the mounting bolts in the back of the bumper.

We usually prefer to use bolts that match the factory nuts however you can just as easily use 1/2" bolts of an appropriate length.   The bolts are then inserted  through the newly drilled holes from the inside of the bumper and into the rear cross member of the Jeep.  It is nice to have someone to help you hold the bumper in place while getting the bolts in place.  Nuts are placed on the bolts and secured in place.  With the bumper tube securely bolted in place you can then reach into the tube and weld the heads of the bolts to the inside of the tube.

While the tube is secured to the back of the Jeep we cut  (2) 4" long pieces of flatbar and drill 1/2" holes in one end of each.  These tabs are then secured in place under the Jeep into the frame with the original bumper bolts.  The tabs are then welded to the bottom of the bumper on each end.  This secures the bumper to the frame in 6 places which we have found to be more than enough.

We then move on to the hinge spindle.  We like to use the 1" spindle and matching bearing set along with a pre-machined hub from Jeeptubes.com.   The spindle has a 1 1/4" shank and a 1" bearing surface.   We measure in from the end of the bumper on the right side (passenger side) 6" and mark a line across the top of the bumper.  This will be the location for the hinge spindle.  The hub is then placed so that it is centered on this line and is flush with the face of the bumper.  You can then put a sharpie maker down the middle of the hub and mark the fore/aft spot for the spindle on the center line.  Since the hub is 2.25" outside diameter then the mark should fall at 1 1/8" back from the front of the bumper.  Center punch this location and using a 1.25" bi-metal hole saw cut a hole in the top of the bumper for the spindle.

Drop the spindle in the hole and square it up using a combination square or a welders magnet.  Weld the spindle on top of the bumper around it's circumference, then weld as much as you can of the spindle on the inside of the bumper.   If you are worried about the spindle moving you can drill a hole in the bottom of the bumper into the bottom of the spindle, tap it and insert a bolt from the bottom up.

The picture at right shows the assembled hinge.  It will more than likely look different than yours however as we machine our spindles on a lathe to different specifications,  however it shouldn't look too much different.  There is a bearing race inserted both top and bottom on the hinge hub and tapered roller bearings are used both top and bottom.  This setup is said to be good for around 1200lbs, much more than you will ever put on the arm with gas, highlift and spare tire.

 

With the hinge assembled you can then set up the swing arm.  The swing arm is constructed using 2" x 3" x .120 tube.  One end of the arm is notched using a 2 1/4" hole saw so that it fits nicely around the hinge hub.  The notch is usually made offset to the rear a bit so that the face of the swing arm is fairly flush with the face of the bumper when it is aligned with the hub.

Once we have the arm notched, we place spacers on top of the bumper to lay the arm on so that we can tack weld it to the hub.  The outer end of the arm near the end should be raised about 1/8" to 3/16" higher than the hub end to add "preload" to the arm as the weight of the spare tire, gas cans and High lift jack will cause the arm to "sag" a bit.   Be sure that the nut on top of the spindle is tightened down as much as you can.  You should hardly be able to turn the hub.  After tacking the arm to the hub we then remove the arm so that we can complete the welding.

Rear bumper build Page 2