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Best Option for Jeep Undercoating Without Removing the Tub

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I'm not sure if this is the right spot or not, but I have a general question, and I'm certainly looking for a technical tip.

I have a 1983 CJ-7 project that has spent most of its life in California and Arizona and is therefore mercifully low-rust. I'm all set to have the exterior painted and the tub interior Rhino Lined next month. I found a local body shop that is going to do both the paint and bedliner, as they are the local Rhino Liner dealer. I prefer Line-X, but there isn't one near me. I'm going to take off all the lights, flares, hinges, windshield, etc. to make sure the paint job can be done right.

The Jeep will be going to Tennessee with me next spring, and I want to get the body well protected before I get into that more humid environment, which brings me to my question: What should I do about the underside?

I don't have the time, space or resources to remove the tub right now, or I would strip it and paint it then. I'm considering POR-15, spray on 3M undercoating, or maybe just self etching primer and chassis black. This will all have to be done in my driveway or possibly the garage, if I can get the junk moved out of the way. I've heard good things about POR-15, but I probably won't be able to get down to bare metal everywhere, which is what they recommend. I like the 3M products, but I've heard horror stories of rust caused when the undercoat had a small void which then trapped salty water against the undersides. Not really sure what to do, and curious what results others have had with these options.

Case

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Case...I was the first person in the U.S. to Rhino coat a Jeep tub.  Rhino dealers were well versed on bed liners.  I had a friend, Rick Preston at Rick's RV Center in El Cajon, who tipped me off about Rhino with his one-ton Ford dually's bed protection.  I was sold on the idea with the caveat you describe:  Any coating must go on a clean and rust free surface without voids!

 

That was 1989, the vehicle was an early-'80s CJ-5 project for OFF-ROAD Magazine, and I publicized Rhino.  I took "Project Trials Machine" to a Rhino franchisee at north San Diego County.  After scratching their heads, they shot the bare tub, fresh out of a light professional primer/sealer job by Louie Russo.  (That vehicle has been depicted in my Jeep Owner's Bible since the First Edition in 1992.)  Today, Jeep tub coating is common.

 

I have used powder coating, professionally applied bed/tub liner, primer/sealer and paint, spray-on undercoating, everything known.  The concern is exactly what you share:  a void can lead to treacherous exfoliation rust (nice for book illustrations but dangerous stuff!).  Exfoliation can occur with powder coating, bed liner, primer and paint, undercoating and any improperly prepped substrate.  The '76-up CJs seem especially rust prone; however, this could also be a reflection on the dramatic increase in the use of salt on winter roads...My CJ-5 suffered from its previous owner's residence at the Rust Belt.  I've heard stories from Michigan friends who have seen Jeep frames split from inside-out rust! 

 

After a half-century of exposure to the bottom sides of Jeep 4x4s, I prefer seeing what's going on with the chassis.  In my view, quality epoxy primer/sealer after complete descaling and cleaning can be a base for a high quality black enamel coating.  Done right and spray washed regularly during salted road months, this can hold up and provide protection.

 

If your goal is undercoating, and if you're confident that there is no rust and everything is sealed well, you might consider a commercial undercoating job by a shop qualified.  They can apply undercoating uniformly and with even chemistry.  If you prefer doing this on your own, 3M does make commercial grade undercoating that could adhere and seal well on a base of black epoxy primer over descaled, clean metal.

 

Between 2005 and 2008, I performed mechanical restoration work on muscle cars and vintage (mostly postwar) classic automobiles and trucks.  The variety of work included rebuilding/restoring vintage manual and automatic transmissions and steering gears.  Iron and aluminum cases were first pressure washed in a cabinet then bead blasted (which left slight etching on aluminum) before spotless cleaning in the cabinet washer with a thorough flash drying.  I found that the best sealing and rust preventative for iron manual transmissions (those that did not require color matching to OEM) was the use of satin or semi-gloss black commercial epoxy primer.  I applied this with a spray gun and used a respirator system to prevent respiratory damage and other health challenges. 

 

Black epoxy semi-gloss leaves a quality, uniform finish with excellent sealing ability.  It works well as a base coat for color, too.  The only downside is that this primer does not tolerate UV well and should not be left exposed to sunlight.  A manual transmission, transfer case, steering gearbox or Jeep undercarriage should never see the sun—if you keep it topside up!  Epoxy primer and quality enamel provide reasonable protection from rock and gravel chipping.  Of course, undercoating over epoxy primer, or a primer/sealer and compatible paint with good adhesion, would provide even more chip protection.

 

I'd like to see others jump into this discussion and comment on their best approach for preventing salted road damage and rust caused by humidity at places like Tennessee!

 

Moses

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Moses,

I agree about being clean and rust free prior to any coating. That's precisely my trouble. I have limited time, no access to a lift, and the property manager probably wouldn't take kindly to running my compressor and HVLP gun in the driveway. I think I'm going to put it on ramps, power wash the underside, wire brush with my drill, and use the POR cleaner, metal prep, and black POR-15. I may try to do the last with a gun, if I can figure out how to get away with it. Don't worry about the health and safety piece. I was an OSHA professional before I started flying Navy helicopters. Practically have my own monogrammed respirator...

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Pleased to know you're taking the safe path...Perhaps we'll have the opportunity to share a high altitude trail some time and can benefit from full lung capacity! 

 

Your approach, given the constraints, makes the best sense.  POR-15 does neutralize rust and should provide a residual effect as well...Keep us posted and share some pics, too! 

 

The rust scourge is real, you're being practical here.  Like your California and Arizona experiences, Nevada is bone dry and rust free.  The '55 CJ-5 featured in my Jeep CJ Rebuilder's Manual: 1946-71 came with exposed bare metal and had set outside for 20 years at Carson City before I found it.  Rust was surface only, easily removed without any sign of stress to underlying sheet metal.  The frame was pristine.  By contrast, a friend from Ohio sent me a Spicer Model 18 transfer case core from a vintage CJ-6.  The Jeep had been subjected to years of salted winter runways at an airport.  Lubricated gears and internals were still intact...The iron case looked "wet" from salt saturation.  It was scrap.

 

Moses

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I know this is an old post but living in Maine rust is a major issue on ALL vehicles. "Fluid Film " has become a standard go to product to prevent or stop rust. It also stops "green death", corrosion on batteries or any electrical connection. My 06 f250 came out of south Texas 4 years ago. No Rust. I have undercoated it each fall for 4 years now. Aside from some surface rust on the frame, the body is rust free!

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Excellent share, Monty!  I'm not familiar with Fluid Film but will now be...I'll look into it.

How do you apply the material, and does it stay in place throughout the year?

Moses

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Our Navy helicopters use a couple fluid film types.  We wipe down most of the exposed metal to prevent corrosion in the salty environments where we work.  A couple of these are similar to WD40, but one version is much more tenacious.  It goes on as a spray but once the solvent evaporates, it leaves a waxy coating that is pretty tough.  You can scratch it off with a fingernail, but it doesn't just wipe off with light contact.

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Fluid film is a Lanolin base product. I use and undercoating gun and spay it on. In time road spray will wash it off.

Also if you got a frozen rusted tool or ???? Spray it and walk away for a few days. I have freed more that 1 item using fluid film.

http://www.fluid-film.com/

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