Underbody coating

[ekimsacul]

so i lucked out and got an 85 cj with minimal rust on the frame, i thought of taking it to a place like ziebart to have it undercoated, but a few have said not to do it, what are your suggustions as to what i should do, i dont mind doing it myself, so what paint/under coating should i use???

 

[Sasquach]

Are you planning on pulling the tub off? Pretty hard to do anything worthwhile without doing so, you would need to remove any rust and properly prep before any coating will stick.
Myself I remove the tub and clean back to bare metal or good paint then repaint similar as factory done, that's obviously allot of work but it's the only way, if not then clean areas you can and rattle can it.
No to undercoating.

 

[johnbilt]

I had the tub off mine and I cleaned all of the old coating down to bare metal or to a firm finish. I tried to make sure that I had a good base or substrate that a new coat would adhere to. A lot of work with a wire wheel on a grinder. A good face shield and some hearing protectors make it more bearable.

I put POR 15 on most of the bare metal. After it cured, I roughed it up with some scotchbrite. I think I also got after it with some PPG wax/grease remover product to get the surface as clean as possible. The prep work is critical. Then I shot the bottom of the tub with Morton truck bedliner mix. It's a tough hard urethane coating that you shoot with a "rocker" gun. Basically it's an air powered gun that sprays or spits out thick materials.

This has held up well for about 10 years now. It seems to have sealed the bottom of the tub and works better than paint.

 

[Busted Knuckles]

Dont mean to piss on your parade (the fact you found a nice 85 as far north as you have), but the salt belt Cjs, the frames usually rust from the inside out..Ive lost count of how many frames Ive seen with an exterior wall with paint, that you could shove a screw driver through. Mostly from the center of the frame on back (4 places in particular).

The salted water gets into the frame via all the holes, where Im pretty sure the factory used nothing on the inside to prevent rot, and then the salt never leaves, just slowly eats the frame over the years.

Ive also been trail riding with clubs and seen frames give way to "unseen" rust under some good flexing, which of course you never see on the road. Ive even witnessed that in CA on a CA Jeepster.

As inexpensive and available the bore scopes are, have a look at the inside of your frame, it it looks great, spend the time and money, if it does not, dont bother.

At the very least, just keep it clean, and try not to drive it on salted roads.