Floor pan rust '83XJ

Howdy,
I just joined, although I've been reading posts for a while. I'm also on the xj listserver at [email protected]. I'm an old Mopar muscle car motor head and this is my first Jeep. My previous rig was an '86 Dodge Ram Charger police special with a 360 Rochester Quadrajet, HP heads, dual roller cam drive, and a 12-bolt limited slip rear end. It was nice, but I LIKE my "new" Jeep.

I've got a stock '93 XJ with 4.0l HO, AW4, an open D-35c rear end, and, oddly, a "dead" pipe front axle out-fitted with 4WD parts. The Jeep is 2WD, but when I order brake pads I have to order 4WD.

Anyway, that's not a problem. This is: floor pan rust-through. It's only just starting, but I don't want to leave it too long. The best (not prettiest) solution we had for that on VW Beetles was to simply pop-rivet on galvanized sheet steel sealed with RTV. Without buying a welding outfit and doing it proper, I thought a treatment similar to the bug fix but prettier might be to attach some aluminum diamond plate. Granted it would have to be sealed up tight but it's something I could work on a little each day without tearing the rig apart.

What do ya' think?

Xj Dreamin'
'93 XJ, 4.0l HO, AW4, open D-35c rear end, "dead" pipe 4WD front

My solution, was to buy a quart of polyester resin, grind everything down to steel, put down a sheet of thin matt and then a layer of glass weave on top, overlapping the matt a bit. Thick coat of undercoating on the underside. 8-10 years later, the rest of the FJ rusted apart, around my patch.
If it´s bad enough, I cut out the cancer and weld in a new (slightly thicker) piece of sheet metal.
PS I´ve got a pre emission orange motor, 360 with the HP stamp, in my garage, factory short spider intake, with a Holly, I´m gonna stick in something someday. Dodge was always pretty good at making horses. Also got a 727 loadflite to go behind it, brand new (kinda) still in the box. Non-lockup, built for a ton and a quarter, manual or auto shift (factory shift kit). Been trying to buy a surplus CJ-10 airport tug, I´ve got a vision. :spin1:

I would not use aluminum, or pop rivets, because if you're in an area where rust is a problem, aluminum will corrode quickly, and pop rivets will leak. RTV also tends not to stick well to very rusty metal, and in my experience it tends to promote rust around the joint.

I have had great success, however, with good old fashioned sheet steel, and self-tapping screws. One of the best sources for good sheet steel is old shower stalls, by the way. Unbeatable - just the right thickness, flat, and already painted with a pretty rust-resistant finish.

Cut out the worst of the rusted metal to form a nice neat hole without very jagged or lacy edges, grind as much as you can down to bare clean steel, then cut a patch enough larger than the hole to have a healthy overlap to sound metal. Paint the edges of the hole liberally with your chosen undercoat/sealant/goo (I have always favored brushable roofing tar), with enough goo to form a gasket when you put on the patch. If it's on a curve, you can just hammer the patch into the rough shape before you put on the goo (this is not outside body work, all it has to do is be strong and seal). Then screw it down with a reasonable number of self-tapping screws. The screws need not produce an absolutely perfect seal, because the goo applied both before and after will do that. All you have to do is make sure the patch doesn't shift or buckle. Shower stall metal is good and stiff, so it won't flex much. I like the little self-drilling screws with 1/4 inch hex heads for this. Finally, paint it over with another very liberal coating of your chosen goo, working the goo into all the little crevices, from both sides, covering the entire patch, and the protruding screws. When it's done it will be hard to see the patch, and unless new holes develop in new areas, the patches will last for years. In fact, they will often last longer than welded-in patches, especially if done in an area where welding would burn out hidden primer and protection.

Thanks 8Mud.
Given that the rust-through is most likely from the inside (lots of spilled diet Cokes 'cause of no cup holders) a coat on the inside would go a long way to delaying the inevitable. However, I didn't say before, but I'm trying to avoid tearing up the carpet or pulling any seats. It's important that the rig stay in service for wife and kid hauling. Also, thanks for reminding me to cut out the active rust. I would have, but I failed to put that in my post.

The vision I have is a cladding of new metal the full length of the under-floorpan, cut and fitted around the bracing channels, rivetted and sealed. This is what we did to the bugs except with galvanized sheet steel. It was a one time fix that out lasted everything else on the car. Of course, we were only driving the bugs because of the fuel prices in the '80's and we had no concern at all for appearances. We just hammered and cut the new sheet metal until it fitted.

I'm thinking diamond plate aluminum because it's pretty, it's pretty tough, and it's light enough to hold on to the original metal without tearing out the rivets. Also, working from the outside with no heat I can avoid tearing out the interior. Do I sound like a total idiot?

Does your vision include any air time?:worship: My Quadrajet was a real PITA but with stock 0.41" lift that HP360 would outrun a Camaro load of highschool kids. Maybe the fact that it was painted red-n-white like an ambulance intimidated them. In no particular hurry, I would routinely step on the gas at a green light and cover a block before the next car had crossed the intersection. I just wish my XJ rear wasn't so wide open. It's annoying when I open the throttle and it doesn't move because somebody's lawn sprinkler is hitting my rear right :sure: I like to move when I open the throttle.

Hey! I'm rambling. Thanks for the advice. I'm thinking now of coating the inside after I get the outside fully cladded and I can afford some out-of-ervice time.

XJ Dreamin'
'93XJ stock, 4.0l HO, AW4, open D-35c rear, dead pipe front axle w/ 4WD hardware, LT235-75R15 A/T's

Matthew Currie said:

I would not use aluminum, or pop rivets, because if you're in an area where rust is a problem, aluminum will corrode quickly, and pop rivets will leak. RTV also tends not to stick well to very rusty metal, and in my experience it tends to promote rust around the joint.

Click to expand...

Well, I do have a nagging concern about dialectric issues with the aluminum. But then, it would take some time to corrode through diamond plate. I don't remember what RTV we used, I was gopher, light holder, and spare hands for my dad at that time, but I don't remember it attracting corrosion. It could have been something he brought home from work (McDonall Douglas Aircraft factory at St. Louis). The rivets do have to be closed end and corrosion resistant, but self-tapping screws are a good idea. I think, because my dad was in the airplane building business, rivets came naturally to him. Self-tapping screws would eliminate the need to pre-drill.

The vision remains, cladding the entire underpan area in some new metal. Even if nobody else sees it, I will, alot I expect in the years to come :repair:

I've got some stuff sold to glue down loose shingles. I wonder if that would make a good patch sealant.

Thanks again,
XJ Dreamin'
'93XJ stock, 4.0l HO, AW4, open D-35c rear, dead pipe front axle w/ 4WD hardware, LT235-75R15 A/T's