No-weld floor pan replacement

[Elwiscon]

Like most MJ’s and XJ’s out there, my 89 had the usual rusted passenger side rust, luckily the driver side only had surface rust. When I bought the truck, i only saw a few small “easy to fix” holes from underneath, when i removed the seat and vinyl flooring i found out that the rust was worse than i expected, the seat stud broke off and the bench seat bracket just crumbled, the unibody cross member was also severely rusted, Did some research and decided to replace the whole floor pan, based on reviews and availability, I bought Keyparts components. See pictures. The hardest part was removing the spot-welded cross member, got me an air chisel and it made a difference, and since I do not have a welder or the skills i went with 3M panel bond and self-tapping screws. I was generous with the adhesive, so i ended up using 3 tubes, with a little leftover to seal gaps and seams. I could’ve replaced the rusted area only but I decided to replace the whole floor pan. I’m not a body technician by any means but I think i did a decent job, hopefully it will hold up. Here’s some basic steps/tips to tackle the job:

 

-WEAR SAFETY GLASSES! I was working under the truck and took mine off for a minute, i got a small drop of 3M adhesive on the corner of the eye, it stings, burns and irritates, i washed it off for a few minutes and it still burned for a while, didn’t go to the doctor as it got better the next day.

-Get an air chisel, plenty of blades for the angle grinder, if you’re leaving the dash and interior pieces while working, cover them, as the hot metal shavings from the grinder may leave burn marks. In my case the interior is gutted except for the steering wheel so no need to protect other plastic components

-If doing the drivers side remember to remove or protect the fuel lines under the truck

-Once the carpet/vinyl is removed, clean/wash the floor, lay the new pan and outline it with a sharpie, measure 2-3 times, before you start cutting, leave 1’ to 1.5” on the existing panel edges, especially front and tranny tunnel to give the new pan a join surface.

-when you’re ready to install, remove rust/paint on the mating areas (existing floor, unibody frame) and new pan, i used a small wire wheel and a flapping disc to expose bare metal.

-Check fitment several times, look for bends, dents, etc.

-When ready to apply glue, clean bare metal mating surfaces with alcohol, acetone, etc. 

-Read instructions on the adhesive, load tube in caulking gun, then start applying, I started on the truck rather than the new pan, WEAR GLOVES, then use a stick/putty knife/finger to spread the adhesive, be generous, best to use too much and have a strong join than have problems down the road for not using enough.

-Set pan on frame, check for fitment, slight bending on the new pan may be necessary for a perfect fit, check all mating surfaces, some goo should spill.

-If everything checks, start driving 1” self tapping screws, pre-drilling the holes with a small bit as you go should speed things up, don’t worry about the adhesive curing, it takes several hours to set and 24-36 to fully cure. Start on one corner and work your way up, I started on the rear corner near the door and worked my way towards the front and tranny tunnel, if that makes sense. 

-if there’s adhesive spilling underneath run a finger on the seams to seal it and minimize water intrusion and eventual rust.

-Let it cure a day or so, then remove screws, panel should be “welded” by now, you can do the floor supports following the same steps, when you remove the old support save the nuts, you’ll need them for the new floor support. Make sure you measure the seat stud holes on the opposite side (drivers in my case) and match on the new support, glue it on, measure again then use screws again, let cure.

-Once it cures, remove screws, fill holes (i used JB weld). 

-Sand off dried excess adhesive (wear dust mask/respirator), prep to paint/finish if desired. In my case I used gray POR15, I will coat it with Raptorliner when I get a chance, will follow up with pictures, I will also raptorline the bottom side as well.

-I plugged the holes with electrical KO seals and JB Weld, I will post pictures 

-I will install new grade 8 bolts/studs for the seat bracket, can’t remember the size, 

 

More pics to follow!

 

Other tips are welcome!

[ghetdjc320]

Your install looks great. Nice prep work . I would point out though, that panel bond is no substitute for spot welding. It’s meant to be used in conjunction with spot welding on structural areas. The Comanche cab essentially has 4 structural horizontal areas, the two rocker panel areas and the two floor braces which also support the bed frame. Using panel bond in conjunction with welding is an excellent technique which essentially seals the joint and prevents moisture from entering. As you pointed out, the original spot welds are very difficult to separate even 30 years later. Fused metal will be much stronger than a chemical bond in an accident. You don't want a "crumple" zone under your seating area . As per TDS below, spot welding through the uncured adhesive is a great technique that provides an awesome sealed bond. 
 

TDS: https://multimedia.3m.com/mws/media/738334O/3m-panel-bonding-adhesive-tds-08116.pdf

 

 

 

 

 

[Elwiscon]

6 hours ago, ghetdjc320 said:

Your install looks great. Nice prep work . I would point out though, that panel bond is no substitute for spot welding. It’s meant to be used in conjunction with spot welding on structural areas. The Comanche cab essentially has 4 structural horizontal areas, the two rocker panel areas and the two floor braces which also support the bed frame. Using panel bond in conjunction with welding is an excellent technique which essentially seals the joint and prevents moisture from entering. As you pointed out, the original spot welds are very difficult to separate even 30 years later. Fused metal will be much stronger than a chemical bond in an accident. You don't want a "crumple" zone under your seating area . As per TDS below, spot welding through the uncured adhesive is a great technique that provides an awesome sealed bond. 
 

TDS: https://multimedia.3m.com/mws/media/738334O/3m-panel-bonding-adhesive-tds-08116.pdf

 

 

 

 

 

True, makes sense, but as I stated, i don’t have the skills to weld floor pans , I ve heard it takes skill to weld thin panels. The unibody frame rails were clean and rust free, so thats a great thing, may provide enough structural support. For additional safety May be a good idea to spot weld it sometime before i finish the floor. As far as i know 3M and other bonding adhesives are great if properly applied. Saw a video on youtube a while ago of a guy doing the same repair with Gorilla Constrution adhesive! Thanks for pointing it out 

[gogmorgo]

Spot welding isn’t too difficult. Much easier than conventional arc welding.
You just have a couple big electrode tongs to stick on either side of your stack and then pull the trigger to fuse everything between the electrodes.

But you do need the spot welder, and electrodes big enough to go around everything. You need to reach pretty deep for those inner welds and it’s a weird angle going up the trans tunnel.

[ghetdjc320]

It sure is great stuff. If jeep had used it back when they were building these Comanches and Cherokees we would have far fewer rust areas and leaks. It may be a good idea to run some sort of fastener all the way from the upper frame cap through the floor pan and into the lower frame support in the same area that the spot welds were done by the factory. I'm thinking rivets with a good rivet gun would work then maybe seam seal the back side with brushable seam sealer. 

[ghetdjc320]

3 minutes ago, gogmorgo said:

Spot welding isn’t too difficult. Much easier than conventional arc welding.
You just have a couple big electrode tongs to stick on either side of your stack and then pull the trigger to fuse everything between the electrodes.

But you do need the spot welder, and electrodes big enough to go around everything. You need to reach pretty deep for those inner welds and it’s a weird angle going up the trans tunnel.

 The actual spot welder doesn't cost much, though I don't know where you could find those big electrodes to fit all the joints. Anyone have a source?

[gogmorgo]

31 minutes ago, ghetdjc320 said:

 The actual spot welder doesn't cost much, though I don't know where you could find those big electrodes to fit all the joints. Anyone have a source?

Not sure if they’re commercially available. There’s a few options on Amazon and eBay but they’re mostly for long reaches, not a long and deep one like you’d need to get around the frame rail. Various tool forums discuss custom making them out of appropriately sized rods with the ends drilled and tapped to screw in standard sized replacement tips.

 

I wonder what an auto body shop would do. Hard to imagine a quick turnaround collision shop would be drilling and plug welding panels in or fully butt welding everything. But I guess you never know. 

[ghetdjc320]

14 minutes ago, gogmorgo said:

Not sure if they’re commercially available. There’s a few options on Amazon and eBay but they’re mostly for long reaches, not a long and deep one like you’d need to get around the frame rail. Various tool forums discuss custom making them out of appropriately sized rods with the ends drilled and tapped to screw in standard sized replacement tips.

 

I wonder what an auto body shop would do. Hard to imagine a quick turnaround collision shop would be drilling and plug welding panels in or fully butt welding everything. But I guess you never know. 

Most body shops i've seen wouldn't touch something structural. They'd probably cut out patches. 

[gogmorgo]

20 minutes ago, ghetdjc320 said:

Most body shops i've seen wouldn't touch something structural. They'd probably cut out patches. 

True, although I was mostly referring to having to reach around stuff with a spot welder. 

[89 MJ]

I drill a 5/16” hole in the top panel, then mig weld the panels together. That’s what my dad does who has been restoring cars for 20+ years does and he learned that working in body shops. 
 

I would’ve liked to see spot welds where the factory spot welds would’ve been for strength, but I do like the panel bond on the outside edges more than when people just tack the floor pan in and brush seam sealer over it. 

[Elwiscon]

I’ll talk to my buddy, he works in a body shop but does mostly painting. Thanks for the suggestions

[Elwiscon]

Here’s more pictures, I used electrical KO seals and JB Weld to close up the floor pan holes, the panels and parts feel really secure with just the adhesive, I’ll look into welding/fastening with some rivets or bolts. Eventually I’ll replace the factory bench with some Corbeau seats, I ordered their brackets and they line up perfectly with the mounting holes/studs , Corbeau part number D848 and D849 see pictures

[pizzaman09]

Well done!  I work for a company that is a competitor to 3M in the panel bonding adhesive market.  It's darn impressive stuff and if used right will massively outperform a welded joint.  I've used panel bonding adhesive to glue on bed sides, rocker panels and portions of floor pans.  It has the nice added benefit of excellent corrosion protection.

 

That said, I do quite like MiG welding these sorts of things too.  One can start at one corner and tack and hammer until the metal is just where you need it.  

[Elwiscon]

2 hours ago, pizzaman09 said:

Well done!  I work for a company that is a competitor to 3M in the panel bonding adhesive market.  It's darn impressive stuff and if used right will massively outperform a welded joint.  I've used panel bonding adhesive to glue on bed sides, rocker panels and portions of floor pans.  It has the nice added benefit of excellent corrosion protection.

 

That said, I do quite like MiG welding these sorts of things too.  One can start at one corner and tack and hammer until the metal is just where you need it.  

Thanks, I did some research before I started, since i have never welded i felt more confident with panel adhesives, saw a few videos where they compared welded joints vs glued joints, in some cases the adhesive is better, but as others stated, fused metal can’t be beat

 

[ghetdjc320]

The combination of both is perfection. The factory left those seems exposed on the bottom trapping water in the butt joint. The panel bond works perfect along with welding to get the sheer strength plus the sealing needed for that area. 
 

I’ve used the technique mentioned by @89MJ with great success. Using a copper backing (I use copper tubing hammered into a flat plate) to act as a heat sink and a backer to fill plug welds. 

[PCO6]

13 hours ago, gogmorgo said:

Not sure if they’re commercially available. There’s a few options on Amazon and eBay but they’re mostly for long reaches, not a long and deep one like you’d need to get around the frame rail. Various tool forums discuss custom making them out of appropriately sized rods with the ends drilled and tapped to screw in standard sized replacement tips.

 

I wonder what an auto body shop would do. Hard to imagine a quick turnaround collision shop would be drilling and plug welding panels in or fully butt welding everything. But I guess you never know. 

 

I don't know if body shops still use welders like a Porta-Spot but they used to be common for attaching patch panels and installing floors, inner fenders, etc.   I bought one used many years ago and its useful for general fabrication too.  You can work from 1 side or both when installing panels.   Unlike the more common spot welders with 2 rods that come together to make a weld, with this one you hold the two pistols about an 1" to 1-1/2" apart and push the button on one of the handles.  It produces 2 spot welds with 1 push of the button. 

 

It's meant for sheet metal to sheet metal welds but I tried it on sliders that I made for my old XJ.   I welded the original sheet metal to 3/16" wall tube and it worked great.   The second pic shows both MIG tacks and spot welds.  

 

 

 

[Elwiscon]

Finally done with the floor! I ended up using steel rivets with 3M panel adhesive, Brushed POR15, Sprayed 3 coats of Raptorliner. Also raptorlined the undercarriage. Once I get the MJ painted and some engine parts replaced I’ll get to the interior. I will line the interior with Dynamat or some sound deadener and carpet.

 

 

[AZJeff]

That nice work.  When you say you used "steel rivets", I see what looks like "pop rivets" in some places.  I assume you mean you used a steel version of those.

 

There are pop rivets out there that require a pneumatic or hydraulic tool to clinch them, and when those are used, in conjunction with structural adhesive, I would bet it would rival the original spot welding done 35 years ago in Toledo.

[Elwiscon]

1 minute ago, AZJeff said:

That nice work.  When you say you used "steel rivets", I see what looks like "pop rivets" in some places.  I assume you mean you used a steel version of those.

 

There are pop rivets out there that require a pneumatic or hydraulic tool to clinch them, and when those are used, in conjunction with structural adhesive, I would bet it would rival the original spot welding done 35 years ago in Toledo.

Thanks, yes they’re steel pop rivets, 3/16’s, i used a cheap hydraulic tool, hopefully they’ll provide additional strength on the frame. Even the adhesive on its own does a great job, I went with the rivets to give it additional support.