For the better part of the past year I've been contemplating making a set of HDPE skids. The OEM skids had worked well but the gas tank skid had a crease that was pressing against the gas tank. That and the fact that the front diff and tranny were unprotected. Last fall's run down Jenny Creek convinced me that better armor was necessary. Problem is, I already have a bunch of added weight on my truck, and I tow a good size travel trailer. I therefore wasn't keen on the extra 140 pounds for the Shrockworks stuff. There is a commercial HDPE skid for the FJ that seems to be working well, so I figured, why not try it.
The next issue was cost. Shipping anything over a 2'x4' sheet would get expensive quick. I came up with a plan to use 2 or 3 sheets this size, but then I'd have to worry about catching the edges where sheets meet on a rock. I made some calls to local plasitcs places and found one that would sell me a 4'x10'x1/2" sheet of HDPE for $185 and there was no freight charge. With this size sheet I could cover the oil pan & front diff, tranny, transfer case, and gas tank with one sheet. I'd also be able to go from frame rail to frame rail.
Here is the sheet on top of the truck.
Based on the density of HDPE, I estimate that the whole sheet weighs 100 lbs.
The next concern was to minimize the span that the HDPE would cross without support. I also needed a way of supporting the skid around the gas tank (especially the aft end). I picked up a couple of 3/16"x-1/2"x4' bars of steel along with a 1/8"x1-1/2"x4' steel angle at Home Depot. With these I fabbed up 3 support pieces.
The angle piece runs frame rail to frame rail behind the TC but in front of the exhaust cross-over.
One piece of flat stock runs from the driver side frame rail to that support that straddles the rear drive shaft.
The last piece of flat stock supports the aft end of the gas tank. It uses the OEM threaded hole near the drive shaft at one and an one in the wheel well at the other.
Since I haven't welded in 25 years, and I wanted these done for Moab, I decided to go with a bolt on solution. Having worked in the aircraft industry, I was familiar with rivnuts and decided these would be a slick solution. I stuck with the 8mm x1.25 thread of the OEM bolts.
With the supports fabbed and the fixation worked out, it was time to start cutting some plastic. First I made a carboard template with all the OEM holes laid out on it. One of the nice things about HDPE is that you can use standard woodworking tools. I used a circular saw for the straight cuts, a jig saw for the inside corners and curves, and a drill for the holes (duh). I rough cut the sheet and then installed it so that I could drill holes through the sheet and frame rails where I wanted them. I then took the sheet off and finished shaping and drilling it.
In order to not have to do a bunch of bending to clear the front diff, TC, gas tank, etc., I chose to make some spacers between the sheet and the relevant frame pieces.
So the skid is now mounted up, minus a few bolts. A quick run to the hardware store will take care of that. Here is a shot of it in the meantime.
My remaining concerns are with the front edge and with heat.
The front edge of the skid is just begging to get caught on a rock. I tried heating it up so that I could bend it to a better profile, but that wasn't enough. I'm going to make a thin metal plate to cover the bottom of the Shrockworks radiatior skid and the front of the HDPE skid.
My concern with heat is that the tranny is now pretty much full enclosed with the CATs. I’ll monitor the tranny temp on my way to Moab and will drill some cooling holes if necessary. I think that there will be enough air flowing through so this won’t be an issue, but I definitely want to watch it. I'll also have to keep an eye on it next time I'm towing.