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How to Keep Your FSJ Floorboards From Pretending to Be Harry Houdini

Contributed by: Michael Baxter

In order to have floorboards in your Full-Size Jeep, you need to have a leak-free body. If you have floor rust, you most likely have water leaks. Full-size Jeep (FSJ) bodies were not changed much from their introduction in 1962 ('63 model year) until the final year of production in 1991. This procedure, in general, should work for any vehicle made during the 29 year production run. Here is my best recollection of the procedures I have used in my quest for stopping the leaks.

You need to perform this procedure on a dry day. Make sure any existing water is completely evaporated by pulling the carpet back a day or two beforehand. You may have to remove the door sill trim in order to be able to pull the carpet back. You can use empty soda cans, screwdrivers, or whatever to prop up the carpet from underneath to allow air to circulate.

You should only test one side of your Jeep at a time for the source of water leaks. Close-up the windows and doors tightly on the side you are planning to test.

My best guess for the tools and supplies that may or may not be required:

  • #2 Phillips screwdrivers in various lengths from stubby to 12" long
  • slotted screw driver
  • 1/4" nut driver
  • ball-peen hammer
  • vacuum with a hose (preferably a shop type)
  • garden hose w/ screw type nozzle
  • 6 or 8 foot step ladder
  • your favorite type of sealant
  • 3/4" wide by 1/4" thick adhesive weather stripping
  • Utility knife
  • Flashlight
  • Duct tape
  • Door panel trim fastener removal tool
  • Allen wrench set
  • 3M Strip Caulk
  • Thick plastic sheet or similar

Remove the air box intake grill at the base of the front window by raising the hood and removing the screws. You will have to carefully tuck the windshield washer spray nozzles back under the hood or you can optionally remove the tubing from the nozzles.

Put the screw type nozzle on the end of a garden hose and stick it inside the air box so that the water can't run over on to the opposite side. The object is to just crack the nozzle on the hose so that some of the water runs and some of it sprays without getting any of water running down the opposite side of the air box or spraying out onto any of the exterior. You don't need much more than a trickle.

Run around and jump in the Jeep on the opposite side from the one being tested. Hold the carpet back and sit there and watch to see if any water starts to form on the floor. You may need to keep a vigilant watch for 10-15 minutes. A flashlight may help. Potential leak areas are any of the metal seams that form the air box and the cable actuated air vents in the each of the kick panels. The seams require looking way up under the dash.

If you get some water coming inside, follow it to the source of the leak. It may be difficult to search with all the wiring and hoses in the way. If you can't see the source, shut off the water and open the door on the offending side for a better view. You may have to drop the under-dash a/c unit down in order to see well.

To drop the under-dash a/c unit: Remove the left-hand a/c vent outlet extension by removing the single screw under the left-hand side of the dash near the interior light or emergency brake release handle. Next remove the single screw that holds the rear bracket to the fire wall above the right-hand foot-well and just behind the air intake on the bottom of the a/c unit. Next remove all the screws that support the front of the a/c unit except the two outside ones. Support the unit with your arm (it's pretty heavy) and remove the last screws. You may have to work with the unit to get it to drop far enough down so you can work.

If you end-up with water running out of the air vents, it is most likely because the drain on that side of the air box is plugged with leaves and dirt. If this happens, you will have to remove the air vent and clean-out the bottom of the air box.

To remove a vent: If you have the under-dash a/c follow the procedure above to drop it down, but don't remove the last two screws. Follow the cable housing until you find where it is attached to the fire wall and remove the screw. Note which opening in the plastic grill that the cable passes through (you can use the other side as an example when you reassemble the vent) and remove the screws that attach the vent. You may have to use a cold chisel, under as much of the edge of the vent as you can get to, to break the asphalt or tar based factory seal. Try to pry it out as carefully as possible, but don't worry if you bend the lip a little as it is easily straightened out on a flat surface with a hammer once the vent is removed.

If you are working on the right-side, you may have to move the under-dash a/c unit up and down several times to remove the air vent screws. If the left side needs to be removed, you need to remove the parking brake actuator (loosen the cable under the vehicle first - two bolts are on the engine-side of the fire wall).

After the vent is free; unhook the cable from the flapper and be careful to mark on which side of the flapper the cable was connected. All the ones I've seen had a tab on both sides of the flapper (so the vent can be used on both the left and right sides). Scrape all the factory sealant off of both the vent and the kick panel. Then you should use the vacuum cleaner to suck out all the crud. Once that's complete use the flat blade screw driver to open up the drain in the bottom of the air box.

As always, re installation is in reverse and you should use the 3/4" weather stripping on the lip around the air vent when you install it back in the hole. Be sure to punch holes in the weather stripping (w/s) for the screws. Otherwise the screws will twist the w/s up.

You can optionally fabricate a piece of 48" wide aluminum screen to fit under the grill at the base of the front window to prevent leaves and such from plugging up the air box drains in the future. I did this and it turned out looking real nice. You can use the air box cover as a template for the screen. If the air box doesn't leak, then get the ladder and position the hose so you can spray water all around the door on the side you are testing. It is important to secure the hose to the ladder somehow so you spend minimal time getting the water to spray correctly. If you spend too much time outside, you may miss seeing the water start to emerge inside.

Turn on the hose and jump in again on the opposite side. Pull the carpet back and again watch for the first signs of a leak.

Potential areas to watch are: Between the bottom of the interior door panel and the door, between w/s and the door and between the back-side of the w/s and the body. It will be obvious which area is the problem as long as you see the water just as it emerges on the inside.

If water emerges from under the door panel, you can stop the water from coming inside by removing the door panel and fabricating a new water shield for the back of the door panel. It would also be wise to replace the w/s around the windows. Mopar has discontinued the wing window w/s by itself (the whole wing window assembly is available), but the rest is available and is relatively inexpensive (compared to a .96 V-8 Grand Cherokee...just kidding :-) ).

Removing a door panel is not tough. Remove the arm rest first, which may require removing the trim under it to gain access to the screws. Use the correct Allen wrench to remove the door handle and window crank. Unscrew the screws at the bottom of the door. Then use the door trim removal tool to pull the trim fasteners out of the door one at a time until the panel is free.

Watch out for the speed nuts that clip into the door to secure the arm rest. They have a tendency to fall in the bottom of the door. Especially when you are reinstalling the door panel.

I used 8 mil plastic sheeting with the door panel as a template to alleviate my leaks. Once I had the sheet cut out to fit the door with all the holes punched using hollow punches, I used 3M Automotive Strip Caulk to glue the plastic sheet to the door (not the door panel).

I have since seen a rubber like material that they use to back shower and bath tub walls in construction which I feel would be better. It's about 3/32 of an inch thick and seems perfect for water proofing a door panel. You can find the stuff in large home improvement stores (Home Depot) in the bath room fixture section. It comes on a 4 ft. wide roll and they sell it by the foot.

There are a couple of louvers at the bottom of the door. The original Jeep water shield (paper-backed rubber) tucked into these louvers You should do the same with the plastic or rubber like stuff. Any water that gets between the door and the plastic backing will drain down and run back into the door through the louvers.

I applied caulk in such a way that any water is channeled to the louvers. There should be enough of the factory caulk left for you to be able to see the general pattern that Jeep used. The caulk line required at the front of the door runs at an angle down to the forward louver. If you have a speaker in the door, completely surround it with a circle of caulk (should also have a plastic shield behind the speaker). You can add an "arch" of caulk between the two louvers to keep water from going between the louvers.

If water comes out between the door and the w/s, then the w/s itself or the alignment of the door is suspect. The w/s around the door is pretty expensive at around $60.00 a door. You may be better off getting it in good shape from a junk yard.

And finally if water emerges from under the door w/s and the body, you can remove it and apply some sealant to the outside of the lip that the w/s slides over. I think this would be a rare problem.

The late 70's Jeep service manuals also have good information on chasing water leaks. They are no longer published and can be hard to find.

My Cherokee is now LEAK-FREE :-) :-) :-). Here is a run down of where I found leaks:

I had a leak in the left hand side of the air box, above the left vent, which would run down the kicker panel. This was a serious leak. It was capable of encasing the carpet in a sheet of ice if the temperature remained below freezing for an extended period.

I had a 1 1/2" gap in the sealant in the left rear wheel well to floor seal. This leak allowed water into the rear passenger foot-well on the driver.s side. Of course, this one didn't.t leak unless the Jeep was driven on wet pavement.

My front window w/s had a minor leak. If it rained hard enough, the right side vent would leak because the drain at the bottom of the air box was near plugged.

I had leaks from behind the door panels on both front doors and a leak from behind the carpeted panel on the tailgate. The tailgate leak was solved by changing the gasket on the tailgate access cover located under the carpeted panel.

Michael Baxter

From Reno, NV USA on 24-Sep-1996

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