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Unread 09-12-2013, 07:39 PM   #1
bwiygul
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Replacing Floorboards but what's the CAUSE for them rusting??

So i'm going to replace my floorboards in my new-to-me 91 Comanche. but i haven't been able to find the reason WHY they rust in the first place.

why are they so prone to it and after i replace them is there a way to make sure the moisture stays out. i'm planning on line-xing the cab floor after the repair but is there a location that let's the water in typically or what?

thanks for all the help you guys.

brandon

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Unread 09-13-2013, 08:22 PM   #2
bwiygul
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Unread 09-13-2013, 09:05 PM   #3
chris87xj
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Carpet and the felt pad underneath soak up moisture and hold it like a sponge, especially with a rubber mat over it. Old degraded door seals are a prime source of moisture entry but there's lots of other ways floor carpet gets wet.
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Unread 09-14-2013, 07:50 AM   #4
Motorcharge
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The terrible paint they used back then didn't help either. If you're going to bedline them inside make sure you do it or use a quality undercoating on the bottom side as well.
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Unread 09-14-2013, 09:24 AM   #5
bwiygul
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cool..thanks guys. is there a better paint if i go that route and should i still coat the underside with a rubberized undercoat or something like that? i just didn't know if there was a culprit location for the moisture build up or something else that was letting water in for years.

help is appreciated! thanks.
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Unread 09-15-2013, 12:43 AM   #6
Motorcharge
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Originally Posted by bwiygul View Post
cool..thanks guys. is there a better paint if i go that route and should i still coat the underside with a rubberized undercoat or something like that? i just didn't know if there was a culprit location for the moisture build up or something else that was letting water in for years.

help is appreciated! thanks.
Like chris said, the door seals are a big spot for water to get in. Especially the passenger side. Water in the glove box is a big indicator of that. You can replace them with 97+ XJ seals for a much better seal. Also make sure all your holes in the firewall are sealed well.

Government regulations on paint (mostly getting rid of lead paint) changed a lot around when early XJs and MJs were manufactured which is why most vehicles made in the late 80s and early 90s had crappy paint jobs that didn't last long. A quality undercoating will work just fine for you. Just make sure to use a good primer on both sides before lining or coating.
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Unread 10-21-2013, 11:11 PM   #7
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2 part paints were used and they peeled on hoods and cabs as well.
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Unread 10-22-2013, 05:19 PM   #8
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If you undercoat the bottom make sure to inspect & clean it thoroughly otherwise you may seal in some rust which would cause problems later . I found water soaked insulation/padding under the carpet that was still wet this past summer even after i pulled it out of the water 4 years or so ago so it sure likes to hold moisture.


Here is a picture of the project iam working on atm it sat in water for 15 something years . The unibody frame supports are still solid surprisingly so its just sheet metal work that needs to be done . I post it as you can see where some of the problematic areas are .

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Unread 10-23-2013, 05:56 AM   #9
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I have found rust holes in the pan area of where my wiper motor sits, even on the pass side where leaves and pine needles collected. Check the back window seals also.
Another thing I don't like is that the front bed drains are very close to draining right on top of the frame allowing added moister inside the frame, which the lowest part of the frame is right under where I see most floorboards starting to rust in that location. I am going to move the drain locations!
side vents - check the seals and also the wing window seals on the doors.
I am also making my floorboard upper frame supports "removable" so I can get in there for inspection every once and a while. Plus, if I ever have to do any future floorboard work, I do not want to remove 100's of spot welds! That's not very fun!
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Unread 10-27-2013, 05:57 PM   #10
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The chemistry of the reaction resulting in the formation of rust can be summarized as follows.
The chemical equations for rust formation

2Fe(s) + 2H2O(l) + O2(g) 2Fe2+(aq) + 4OH-(aq)
Fe2+(aq) + 2OH-(aq) Fe(OH)2(s)
Fe(OH)2(s) =O2=> Fe(OH)3(s)
Fe(OH)3(s) =dehydrates=> Fe2O3.nH2O(s) or rust
The chemical formula for rust is Fe2O3.nH2O
The overall chemical equation for the formation of rust is
Iron + water + oxygen rust
4 Fe(s) + 6 H2O(l) + 3 O2(g) 4 Fe(OH)3(s)
Iron(III) hydroxide, Fe(OH)3 then dehydrates to produce Fe2O3.nH2O(s) or rust
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Unread 10-27-2013, 06:39 PM   #11
87MJTim
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Check the seal on the side window vents. These things are prone to leaking. Jeep knew about it and could not fix it. Until they discontinued the vents.
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Unread 10-27-2013, 07:11 PM   #12
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Quote:
Originally Posted by Live4Jeeps View Post
The chemistry of the reaction resulting in the formation of rust can be summarized as follows.
The chemical equations for rust formation

2Fe(s) + 2H2O(l) + O2(g) 2Fe2+(aq) + 4OH-(aq)
Fe2+(aq) + 2OH-(aq) Fe(OH)2(s)
Fe(OH)2(s) =O2=> Fe(OH)3(s)
Fe(OH)3(s) =dehydrates=> Fe2O3.nH2O(s) or rust
The chemical formula for rust is Fe2O3.nH2O
The overall chemical equation for the formation of rust is
Iron + water + oxygen rust
4 Fe(s) + 6 H2O(l) + 3 O2(g) 4 Fe(OH)3(s)
Iron(III) hydroxide, Fe(OH)3 then dehydrates to produce Fe2O3.nH2O(s) or rust
Therefore, isolate any of the 3 variables from the others and rust cannot occur.
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