By: John Nutter - 3/2002
TJ Flat Skid Plate and Raised Gas Tank
Do you need more ground clearance on your TJ but don't want to add more suspension lift or bigger tires? A flat skid plate may be the answer for you. We will take you through the install of a flat skid plate and the other parts necessary to make it work, and as a bonus we will show you what we did to improve ground clearance under the gas tank at the same time.
|The flat skid.|
|The factory skid.|
|MORE raised motor mounts.|
|Keith and Dave work on the body lift. Installing the rubber bumpers at the corners of the grill may have been the hardest part of the entire project.|
|The complated body lift.|
|The top of the flat skid. Note the raised pad for the transmission mount|
|Counter sunk holes and flat head allen bolts for mounting to the frame are a nice touch.|
|Don Ryman shows off his flat skid plate compared to the factory skid plate.|
|The gas tank sitting on the Tera gas tank skid plate with the top rear section cut off.|
|Dave and Keith try to attach the rubber pads to the gas tank. It turned out to be easier to slip them in place at the last moment.|
|Dave and Keith ham it up with the modified Tera gas tank skid plate.|
|The modified gas tank skid plate in place.|
|This shows how far off we were from having an acceptable amount of droop travel on the drive shaft after the skid plate was installed.|
|One of the places where we ground on the CV.|
|The 2" raised motor mount next to the unmodified 1" raised motor mount.|
|The arrow shows where we had to cut away part of the cast motor mount.|
|The spot where we had to grind on the transfer case yoke.|
|The drive shaft has enough down travel now.|
The factory skid plate on the Jeep TJ isn't bad, but it could be better. The hang down seems to be the result of compromising ground clearance in order to keep the rear drive line angle acceptable with the long stock tail shaft. Clearance issues between the transfer case and body probably contributed to the low hanging skid plate as well. The Jeep we installed the skid plate on already had a slip yoke eliminator, CV style rear drive shaft, 4" suspension lift, 1" coil spacers, a Ford 8.8 rear axle and a Tera gas tank skid plate. If you don't have a slip yoke eliminator and CV rear drive shaft, plan on purchasing them as part of this project. The Jeep in this article belongs to Keith Thomas and the skid plate was made by Don Ryman, both of the Mn Trailriders 4x4 club. This is a good example of the advantages of being a member of a 4x4 club, but any good welding shop should be able to make up a flat skid plate for you using your original plate as a template for hole location.
Installing the Skid Plate
To fit the new skid plate we had to move the motor, transmission and transfer case up about 2". The raised drive train meant that we needed to start the project by installing a 2" body lift. When looking at 2" body lifts, be sure to get a complete kit with a riser for the pillow block bearing on the steering shaft and drops for the rubber bumpers at the lower corners of the grill. The body lift was easy to install, anyone with a floor jack should be able to complete that part of the project in a couple of hours. Be sure to read the instructions and follow them in the correct order. Disconnect the transfer case shift linkage before you raise the body and leave it disconnected for now.
In addition to the 2" body lift, you will also need to install 1" raised motor mounts if you are going to install a flat skid plate. Because you are raising both the motor and the body, you may not need to lower the radiator. The motor mounts are even easier to install than the body lift. To install them, put a board across the top of your floor jack and support the motor. Remove the original motor mounts and raise the motor enough to put the new mounts in place. The nuts for the outside bolts are welded to the frame and the bolts on the side of the mounts are welded to the mounts themselves, making removal and replacement of the mounts very easy. If the motor shifts, a come along or pry bar will help you line up the holes.
With the body lift and raised motor mounts in place, it's time to drop the factory skid plate off and raise the transmission and transfer case to their new height. Because the body is 2" higher from the body lift and the motor is raised 1" by the new MORE motor mounts and the transmission and transfer case are raised 2" from the flat skid, there's no need for the part of the body lift that drops the transfer case shifter linkage down. Use your floor jack and a block of wood to support the transmission ahead of the skid plate and remove the original skid plate. Raise the transmission to it's new height and re-connect the transfer case shift linkage and finally install the new skid plate. 3.5" of clearance were gained by raising the transmission and transfer case only 2".
More clearance under the gas tank
With the skid plate in place we moved to the gas tank area to see what we could do for extra ground clearance. While it would seem that we should have been able to raise the gas tank 2" because of the body lift, it turned out that there was a frame cross member that limited how high we could raise the front of the tank. We began by dropping the Tera gas tank skid plate, the stock skid plate and the tank at the same time. These items were supported by a floor jack and block of wood, unbolted and disconnected and lowered. Make sure to get the lines and wires disconnected before you lower the tank.
With the tank and skid plates out, we marked the Tera skid plate 2" down from the top flange on the back and cut across it with a reciprocating (sawzall type) saw. The top flange from the rear of the Tera gas tank skid was bolted back in place on th Jeep. The lower part of the Tera gas tank skid was set on the block of wood on the floor jack and then the tank was placed directly on the Tera skid. The stock skid and straps were discarded at this time. The tank and the lower half of the Tera skid were raised into place to check the fit. Rather than use straps to hold down the tank, thick rubber pads were placed between the tank and frame cross member and the skid was used to cinch things up tight. The lines and wires going to the gas tank need to be routed over the top of the cross member above the gas tank becuase the tank will be held tight against crossmember.
With the tank and rubber pads in position, the 2 parts of the Tera skid over lapped in the back by 1 1/2". These were clamped together and tack welded. The skid and tank were removed one more time and the gas tank was taken a safe distance away while we welded all the way across the back side of the skid. A piece of angle iron was also added to the skid to make use of the 2 extra studs on the back that weren't being used by the stock gas tank skid plate any more. After the welding was done and the skid was allowed to cool, the skid and tank were raised again and the back was bolted in place. The rubber pads were carefully positioned to make sure the plastic tank wouldn't be ruined by rubbing on the frame and then the jack was used to raise the front of the tank as far as possible. The front bracket for the Tera gas tank skid plate was marked for modification, removed, modified and replaced. The front of the tank was only a little higher than before, but 3" of ground clearance were gained at the back. The 3" of extra clearance at the back of the tank should be very beneficial since that is the part that normally receives the most attention from rocks on the trail.
A lot of ground clearance had been gained, but now it was time to see what problems had arisen from this. The most obvious problem was the pinion angle needed to be adjusted. A secondary problem was the CV in the rear driveshaft was binding before the axle hit full droop. The droop problem was a serious issue becuase if left this way Keith would break the CV centering mechanism any time he got high centered. Keith had adjustable lower control arms, but these didn't have enough room left to make the pinion angle correct. Keith's Ford 8.8 rear was installed using Rubicon Express brackets, and these don't have the provision for the cam bolts on the upper control arms like the factory brackets do, so that option is also out. Keith bought a set of adjustable upper control arms which easily resolved the pinion angle issue. Adjusting the pinion angle also helped with the drive shaft droop issue becuase the pinion ended up higher than before. This was still not enough though. The next step was to gind on the CV with a die grinder. Any place where the CV parts rubbed together at the full angle got a little attention. This helped a little more, but the drive shaft was still binding before full droop.
After some discussion, Keith and I decided that raising his motor an extra inch might help. The MORE motor mounts had already raised it an inch, and Keith came up with an easy way to get an extra inch out of them. The motor mounts were cut apart and a piece of 2" x 1" x 3/16" tubing was welded between the bottom plate and the uprights on the mounts. When we tried to install the 2" motor mounts we realized why no one was selling these as a ready made product. The cast mounting bracket on the passenger side of the engine hits on the frame mount before you get the engine raised 2". We trimmed this portion of the bracket off and had no further problems with installing the 2" mounts. This got the droop very close, but still not quite there. After spinning the driveshaft around and looking for the cause of the binding we found one more place to grind. The yoke on Keith's slip yoke eliminator had some corners that stuck out and hit on the CV. A quick touch with the angle grinder on each of these and we had more than enough droop on the CV.
Thanks go out to Dave Stauffer for helping us wrench all day. Thanks also go out to Don Ryman for stopping by and lending his expertise on the project.