Fix Your Bent Undercarriage Protection
Updated January 6, 2010
Just about every time I go out 4 wheeling I somehow end up landing on the bottom of the truck. Luckily the Hummer has undercarriage protection made out of 1" diameter tube with a wall thickness of .223" welded into a lattice. The undercarriage protection is bolted to the underside of the truck. The problem comes in when an 8000 pound truck comes down hard on a rock and bends the undercarriage protection.
The first time it happened was in Moab Utah about 3 or 4 years ago. I was getting strange vibrations and noises in the truck while I was moving. I rolled under the truck for a look-see and discovered what had happened. A couple of the undercarriage protection bars were in contact with the exhaust pipe. It turned out that the whole lattice was pushed up about 1/2". It was mostly bent at the frame mounting point. I know some owners take the undercarriage off and use different means to bend it back. The ideal method is to have a frame machine. One of the guys at the event showed me a really neat trick.. This is the ultimate portable frame machine.
This picture is taken looking towards the front of the truck. See how the mounting bracket is bent up. Too fix it you need at least a 3 ton jack, logging chain and a wood block.
You wrap the chain under the base of the jack out by the wheels. You place the chain up and over the bars in the undercarriage protection that you want to pull down. Take all the slack out of the chain and raise the front of the jack about an inch. Fasten the chain together with the hook. Put the wood block on the jack and position it directly under the frame rail of the truck. Slowly start raising the jack making sure the block comes in contact with the frame. As you continue jacking the undercarriage will be pulled back down. Jack past the point you want because the steel will spring back. It's usually necessary to move the jack to a number of positions on both sides of the truck.
There is a lot of tension involved in this method so get out from under the truck and make sure everyone stays away while you are jacking. If the chain or jack breaks you could suffer great bodily injury.
Notice how the bracket is now straight. You can now see the a flat spot on the exhaust pipe made by the bars. Now there is clearance between the exhaust and the bars.