Interior rust

[TheJeepNut]

Hi all.  As I've explained to some members who've posted to the Street Comanche Registry, I've not been active over the last 5 or 6 years as my wife battled cancer.  She lost that battle last May and it's been (still is) tough.  But I'm finally returning to other things important in my life and it's been a long while since anything substantial was done with #24.

 

I didn't read closely enough or thoroughly enough Pete's ongoing mantra about pulling up the carpet.  I didn't have a spot of rust on the exterior, under, on any fenders, or doors, didn't think I really had to worry.  I missed the part about other water entry points...sigh.  Some time ago I discovered the carpeting wet and found the sunroof had been leaking ever so slightly but for ever so long apparently.

But in the process of getting my feet wet with restarting the project I note water entry / rust in some unexpected places.  At least the master cylinder hasn't eaten up the fusebox assy.  So that's a bonus.

 

I've not yet posted new images or made updates on my build sheet but owe the site a lot of attention as well and plan to get that done very soon.

 

Meanwhile I come seeking wisdom and experience.  Now that the interior is fully stripped, I pulled the fuse box assy apart and note that there is evidence that water seeped past and into the interior.

What I did not expect was to find that the same water had infiltrated UNDER the seam sealer.  I can only presume that the surface wasn't prepared correctly or the sealer SHOULD have been well connected as it is in most places.  But now I'm leary of ALL the seam sealer.  Am I crazy to think it ALL has to be somehow removed to check to see if it's eaten up underneath?  GAWD there's a lot of seam sealer... Is it overkill?  Should just look maybe for loose edges and cracks (which I've found).   I've pulled the sealer out of a corner where it was cracked by 1/4" x 1" so I pried it out.

Sure enough rusty metal underneath.  Just surface rust at that specific point but ...concern seems justified.

 

So you experienced bodymen.... take a look at the images and tell me... what do I do / have done?  I'll live another 20 years if I'm lucky and if I'm still driving that long even LUCKIER... but I want it fixed RIGHT not halfassed.  The truck may well be passed to a grandkid going forward... not quite sure what to do with this in my will frankly, if it ever becomes worthwhile to will to someone... and not to be morose but... think about it folks... who gets YOUR projects...lol  It WILL become an issue... pun fully intended.

 

But similarly (and apologies for not having the correct terminology, but there is this sort of  U Shaped channel with flanges that is spot welded to the floorpan in the cab.

It essentially acts as support and I'm supposing as part of the Uni-Frame section under the cab.  It's kind of like the cab floorpan is sandwiched between a deeper U shape under the pan and a shallower U shape on top of the pan, creating a defacto "frame" unit, integrating the cab floorpans.

So  this top channel is ate UP with pockmarks millimeters deep in the front 1/3 of it's length. 

Do I need to replace that channel?  or just fill and paint?

I've bought a full left floorpan to resolve what holes that I KNOW are there, delivery pending...

But how does that work.  Do I need to grind out every single one of those spot welds, UNweld the studs that mount thorough it, UNweld the side frame rail that runs to the driver's door opening and take ALL that off to cut out and weld in the floor pans?  What about that uchannel frame section below?

 

Those who know.... how does that work exactly to replace the floorpan?  Can't see how you'd do it without "disassembling" the frame in that area....sounds like a bad idea.

 Yet they sell this full cab length floorpan...

 

He'p me, he'p me...  LOL

 

 

 

 

[Pete M]

I would clean it allllllll up.  scrape everything off in the affected area, drill out the spot wells for the frame cap to pull that up, and see what all you're dealing with.  if you only have a few tiny pinholes, you're in excellent shape.   

[eaglescout526]

Yeah I thought the same thing too for having an AZ MJ only to find myself replacing the drivers side floor. 

[Minuit]

No easy way around it. All of the seam sealer needs to be scraped up (it loves to trap water), all of the pieces that make up the floor assembly need to be separated, each needs to be evaluated separately, and the underside of every panel needs to be thoroughly de-rusted and primed+painted. Get a borescope camera to look inside the uniframe. If any rust is found on the bottom of the main floor pan panel or the interior of the uniframe, the main floor pan is going to have to be cut out to gain access to the interior of the uniframe, the rust dealt with, and the piece you cut out welded back in. Once that's done, the interior needs to be waterproofed - that most likely means pulling the HVAC box and making new gaskets, packing the wiring bulkhead connector with waterproof grease and maybe running a bead of RTV silicone around it, and addressing any other leak points as necessary. There are no short cuts and no steps that can be skipped. It's invasive, but less invasive than replacing every bit of metal in the floor in a few years if you ignore it.

 

[TheJeepNut]

Awesome.  lol

I kinda thought that might be the general consensus but not having been down this road it's a little scary so I needed the confirmations.

 

Nice drawing Minuit!  It's exactly what I presumed this package looks like.  GIMP is hella nice but I'm not bright enough to figure it out.  I recently added Shutter to my CentOS system.  That's what I've used on my images to mark them up.  But not a software thread so...

I'm a  tool junkie so just dropped an order with King Bezos on an endo/boroscope kit.  Had a $15 plug in camera but never could get it to work with the Blackberry which rarely works anymore itself so I've abandoned both and guess I'm done with wasting money on THAT technology.  My old landline works great.

 

Next questions:

1.  Issues with supporting the underside of the vehicle somehow while I essentially destroy it's ability to NOT fold in the middle of the cab once I take off the top cap?  Or will that not cause any issue?

2.  How about if I need to pull the lower UFrame Channel as well.  Need to brace it up if that is necessary?   Or will the rest of the cab assy and other side be enough support for temporary work?  If you've not guessed, I'm not a structural engineer.

3.  Once I drill out the spot welds, assuming I drill all the way through with a bit about the size of the weld spots... makes me wonder... will the lower frame channel drop off the truck too?  Or will it need to be seperated?  What about that top channel and side brace?

Thinking  I don't want to pry on them if I'm gonna bend up thin metal.  Anything to consider here?  Perhaps just a heavy flat scraper tapped under will seperate them?

 

There is nothing in the interior, no seats, dash, no weight other than the windsheild and rear windows are still intact.  Bed is still mounted on the rear frame assy.

It's still got the full suspension under it so is sitting on jackstands under the "axles".

The engine is still in it, no tranny or shaft.

 

Gonna spend the day with a heat gun it seems!  LOL

Thanks all!

[Pete M]

most guys don't bother putting the top cap back.   

[Minuit]

I, however, tend to go with "the engineers designed it that way for a reason" and will be putting it back in, pain in the @$$ that may be. I already pretty much know I'll be fabbing it from scratch on the driver side. I want to end up with a truck that is just as rigid if not more rigid than when it left the factory, and putting just the single-skin floor pan back in won't cut it for me.

 

Caveat: most people don't spend much time thinking their floor pan jobs through, and their trucks generally don't end up folding in half. I, however, currently have nothing but time to think things through and I want to end up with a nice looking floor pan at the end.

 

1. For REALLY invasive repairs, my go-to suggestion would be to weld in some temporary bracing. However, if you are only cutting out small sections of the floor - I wouldn't worry too much. Your truck doesn't look too bad based on what you've shared. That's maybe a 3/10, with a 1/10 being a perfectly pristine floor and 10/10 being nothing left. This is what I have to work with, and I'd call it a 6 or a 7 on that scale. This looks really bad, but the uniframe channel is still good underneath.

 

Here it is right now. I still have quite a bit of rust to cut out before I can begin building back up, but the uniframe channel is still in excellent shape, thankfully. What you see inside of it is mostly just rust flakes from the layers above crumbling. My next move will be to finish drilling the longitudinal brace's spotwelds, remove the rest of it, and see what the condition of the metal is underneath. Also, most of the transmission tunnel and the lower firewall behind the pedals needs to be cut down to good metal. You have less work to do than I do.

 

2. You won't be "pulling" the lower uniframe channel - it's connected to the suspension at either end and really not a removable part. You'll be removing things FROM it, not removing it as a unit. Unless your truck is REALLY rusty, the most common thing to find is a totally destroyed floor pan but an otherwise OK uniframe with a bunch of nasty rust flakes sitting in it. That was the case on my 89, which had it much worse than your truck does. On my 89? Those flat sections on either side of the uniframe? Gone. The interior of the uniframe channel looks perfect.

 

3. Get a set of Blair Rotabroach spot weld cutters. The 7/16" size has done well for me. The most common size is 3/8", but I've found that's a little too small for the spot welds on this truck. It's more accurate to say you drill "around" the spot weld, and you do not go all the way through. You just drill until whatever you want to take off is free to move. Repeat that for every spot weld on the panel and afterwards the actual spot welds remain attached to the truck. You grind those off, do whatever you need to do underneath the piece you took off, and then plug weld the panel back on where the spot welds were.

[TheJeepNut]

23 hours ago, Minuit said:

I, however, tend to go with "the engineers designed it that way for a reason"..

 

 

And that's me as well.  It may be overkill but it's the "right" way in my head anyway.  Not that I won't make IMPROVEMENTS to the factory's efforts...lol

And what a brilliant response.  Thanks very much.  Got to looking at some video and I guess I should stop whining.  MY rust issues are quite minor by comparison.

Still... they bug me.  And I do what this to pass down to someone once I'm done with it.

 

23 hours ago, Minuit said:

You grind those off, do whatever you need to do underneath the piece you took off, and then plug weld the panel back on where the spot welds wer

 

Showing my lack of experience again.... diff between a "spot" weld and a "plug" weld?  I probably WON'T be doing the welding tho I've got a li'l wire feed welder.

I've not done much but "farm" welding at this point.  Pieces that don't' have to be nice and nothing fancy.  I'm not sure I want to start training on THIS truck.  My bodyman is great and has done some jobs for me that are outstanding but he moved on me so doesn't get around often anymore.  I'll end up taking it to him for bodywork and paint once I get it prepped some, or maybe he'll come here to do these floorpans.  I need to call him anyway....

[JustEmptyEveryPocket]

Spot Weld:

 

Plug Weld:

[Minuit]

[AZJeff]

On 4/21/2020 at 11:35 AM, Minuit said:

I, however, tend to go with "the engineers designed it that way for a reason" and will be putting it back in, pain in the @$$ that may be. I already pretty much know I'll be fabbing it from scratch on the driver side. I want to end up with a truck that is just as rigid if not more rigid than when it left the factory, and putting just the single-skin floor pan back in won't cut it for me.

 

 

While I agree that (as a retired engineer), the 'designed it that way for a reason' is a good logic, keep in mind that the XJ did NOT have this added "hat section" welded to the top of the floor pan.   They only relied on just the  lower "hat section" that forms the uniframe with the floor pan for that vehicle.

 

Putting on my mechanical engineer hat here, I suspect the issue has to do with the fact that the MJ lacks a roof that extends all the way to the rear of the vehicle, and the transition point from the cab to the "pickup truck frame" section is a critical point in the chassis stiffness, and adding this hat section added some stiffness.  

 

HOWEVER.......The size of those hat sections, and thus the amounted of added stiffness they provide, is NOT significant (compared to the lower uniframe hat sections), so I do not know if their loss would be monumental.

 

One can duplicate the added stiffness of those hat sections in a variety of other ways, not the least of which is plating the sides of the uniframe on the bottom of the floor pan.

 

My point is that the loss of the upper hat sections is not SUPER critical, but if you feel you need to add stiffness, there are other ways to do that that might actually be BETTER (but were not done by Jeep for economic reasons.)

[Minuit]

1 hour ago, AZJeff said:

While I agree that (as a retired engineer), the 'designed it that way for a reason' is a good logic, keep in mind that the XJ did NOT have this added "hat section" welded to the top of the floor pan.   They only relied on just the  lower "hat section" that forms the uniframe with the floor pan for that vehicle.

 

Putting on my mechanical engineer hat here, I suspect the issue has to do with the fact that the MJ lacks a roof that extends all the way to the rear of the vehicle, and the transition point from the cab to the "pickup truck frame" section is a critical point in the chassis stiffness, and adding this hat section added some stiffness.  

 

HOWEVER.......The size of those hat sections, and thus the amounted of added stiffness they provide, is NOT significant (compared to the lower uniframe hat sections), so I do not know if their loss would be monumental.

 

One can duplicate the added stiffness of those hat sections in a variety of other ways, not the least of which is plating the sides of the uniframe on the bottom of the floor pan.

 

My point is that the loss of the upper hat sections is not SUPER critical, but if you feel you need to add stiffness, there are other ways to do that that might actually be BETTER (but were not done by Jeep for economic reasons.)

I will now proceed to defend what I said. I intend no disrespect and I trust your judgment on matters of structural rigidity probably more than any other member on this forum, but I have my reasons for saying what I said.

 

For my specific situation:

1. I have an education in mechanical engineering too, and I concur that we're talking about maybe a few percent difference at most. But, I currently have no realistic way to prove that the upper frame brace doesn't have a significant effect on the stiffness of the truck sitting in front of me, so I choose to err on the side of caution for my build. If I still had access to the FEA programs I used in school, it would be a fun project to build a model of the floor system with and without the brace and see just how much that piece matters. What I can say is that there's no way it doesn't reduce the truck's stiffness in at least some way, and that's good enough for me.

 

2. I'm partially doing it the stubborn, difficult way as an exercise in fabrication. I haven't done much work with sheet metal before and I want to learn. I just got told I can't drive on public roads for 6 months for medical reasons, so I've got nothing but time to do things the slow way.

 

3. Plenty of people do exactly what you mention and end up just fine, including some people who are doing what I'd consider to be pretty high grade restorations. This is just another case of me being picky.

 

4. My upper frame brace has catastrophic damage past where the seat mounting studs attach to it, and I don't really want to redesign the way the seat attaches to the floor pan, so I'm just going to copy the factory piece when I rebuild it.

 

5. Duplicating the factory design will make the carpet fit like it should. Yeah, that's something I'm willing to go to the effort for.

 

6. I take a lot of pleasure in the concept of "doing a lot of work to make it look like I did nothing" and that extends to duplicating the factory design of the floor pan and not adding any extra bracing even if it would make the truck stiffer. I want my truck's floor to look completely original when I'm done, even if there couldn't be anything further from the truth. We'll see if I achieve that goal in the end, but it'd be nice if I did.

 

7. Approximately NOBODY puts that brace back in when they do a floor pan in these trucks, and I just like doing things a little different. I'm the Jeep restoration world's version of a hipster.

 

8. The MJ's unibody was designed to handle much heavier payloads than the XJ's unibody and those loads are also concentrated in different places, which I'm sure is the actual explanation for why the MJ's floor pan has so much extra bracing that isn't present on the XJ, and I'm sure that layering in some more stampings was probably the cheapest way to achieve that for AMC. It was also designed after the XJ, so we might be seeing some things that the engineers wished they would've done on the XJ in the design of the MJ. I wasn't there, so I don't know. But for those reasons I don't consider "the XJ did it like this, so it's fine on an MJ" a valid argument if we're really going to be picky.

 

For our OP's situation:

 

1. The OP is clearly someone who thinks something through and is interested in doing things the right way. Very few people on this forum go to the effort to give us annotated pictures of their truck's rust situation to start off a help thread. When I see something like that, I think "hmm, that person seems like a detail-oriented guy. I'm a detail-oriented guy. Maybe I should open up a little more on my point of view than normal." I don't think TheJeepNut would be dangerously affecting his vehicle's structural strength if he decided to just throw that upper frame brace in the garbage, but the way he phrased his post made me think that I'm not wasting my time when I write up a long post about why he might want to think about doing it the way the factory did it.

 

2. In the grand scheme of things, his truck isn't rusted too bad. But he really needs to look under that brace to make sure there isn't more rust being hidden by the brace, so it's coming up anyway. If anyone stands a chance of being able to drill the spot welds on the brace, clean it up with a wire wheel and make a simple patch for the section with pinholes, and then weld the brace back in place without doing any re-engineering, it's him. My floor pan is a total loss, and I'm choosing to duplicate the factory design because I want to. But for him, that's legitimately the easiest way to go about this and still do a complete job.

 

We can still be friends, right?

 

[AZJeff]

As an "old school" ME (FEA did not come along until I was in management, so I only know the theory, and have never actually used it), here is my take:

 

If you have interior hat sections that are reusable, by all means, reuse them (with appropriate plug welds as shown in photos elsewhere in this thread.)

 

If your interior hat sections are trashed (or missing) and you want to achieve OEM stiffness (or better), plating the sides of the uniframe will do more to improve the moment of inertia of the "frame" of an MJ that those silly hat sections would ever do.

 

And yes, we can be friend, both profession career wise and otherwise.

 

Don't you LOVE it when engineers start arguing the best way to do something?

[JustEmptyEveryPocket]

*This reply in no way applies to the OPs questions*

 

Minuit- 

23 minutes ago, Minuit said:

Approximately NOBODY puts that brace back

My truck was not nearly as bad as your photos, but I still rebuilt all the parts, hat and brace included. Brand new shiny metal welded in place and kept looking (fairly) stock. It was two days of hard work but worth it. All that to say: "You are not alone". 

 

And then to ruin it for you --> After I got the brand new metal in and seamsealed I sprayed it over with POR-15 (properly prepared), followed by four coats of LizardSkin, and two layers of topcoating. No more carpet and definitely not stock looking. 

[TheJeepNut]

Nice discussion!  I'd put all this to the Street Comanches new home but I've not added in all the previous detail there yet.

I got the boroscope and that's fun.  Inside the lower frame channel looks amazingly good.  A few spots here and there that just look surface rusty...

 

Just got the Rotabroach tools & some lube and have looked over pretty extensively what I'm about to do and have more questions and comments.

 

My buddy who's my body & paint expert just had a heart attack so I MAY end up actually being the one to do this welding.  I'm going to be practicing first obviously on some scrap to see if I can even lay a decent bead.  Wish me luck.  If it's ugly I'll seek an alternate for sure.

 

Also have been on the Eastwood site and raised even more questions.

1.  In terms of the lower box frame I think the appropriate product is Eastwoods Heavy Duty Anti Rust (Amber).  It doesn't require any attention once sprayed in and penetrates through to seal and prevent further rust.   Alternate ideas?

In terms of the floorpan.  In this image....

 

 

See those multiple "spots" in the inverted U shape there where welding was done during assembly....  The factory slopped seam sealer over it all.  All of the "gray" area there in the upper 2/3 of that image is where I scraped off the seam sealer.

 

And I have this really rough rusty metal that I'm not going to replace.  It's double thick there with a panel opposite the firewall and is not at all soft even though it looks pretty eaten away. 

Specifically the area just below and to the right of the fuseblock.  But all the metal around that little stud sticking out there is pretty rough but doesn't "give" at all when probed with my implement of destruction...

 

 

 

 

2.  Should I just shoot  Eastwood Rust Encapsulator over all of that and then put seam sealer over the areas where it was before? 
I'm thinking I might spray the ENTIRE lower half inside the cab with Rust Encapsulator.  Bad idea, good idea?

 

I wasn't sure if the Rust Encapsulator should get seam sealer over it or not.  Apparently both can be painted.  Seam sealer didn't seem to be all that helpful in stopping rust so I THINK first Rust Encapsulator and then seam sealer but I don't know for sure.

 

 

3.  I don't think I want to use this entire floorpan piece I bought.   I think I am going to cut the floor pan along the yellow line.

 

 

My question here is do I overlay the edges 1" and weld top and bottom along the yellow line?  or do my damnest to butt them, tack and weld in sections?

The back 1/3 of it is solid anyway, but complicating matters is this brace that's spot welded from up on the trans/shaft tunnel wraps under the floor and over into the lower boxed framerail section.  It seems it would be hella difficult to extract intact.

 

 

It is seat support and seat BELT support and I think I should leave that all alone.  Marked out in Blue on the floorpan.

 

Thoughts?

 

[watchamakalit]

Butt weld.  Forget the overlap idea I have tried that on MJs before.  You will end up trapping moisture between the 2 pieces and simply continuing the rust cycle.  Butt welding isn't that hard.  There are some great tips and tricks that can be learned online for free that will help you a bunch.  Let me finish this by saying, I am not a body guy by any means.  I have just attempeted several methods of metal repair previously and can tell you what won't work.