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Root cause for rear seat rust and preventative fix


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As we know there is a design flaw on the WD21 which causes the rear seat floor to rust out.

 

You won't see the rust "until it's too late" - the reason being there are multiple reinforcement plates in this area and it's rusting from the inside-out due to water ingress between the plates. Everyone should have this issue although it's going to be exaggerated if you live in the rust belt.

 

I believe I have identified where the water is coming from. There is a chassis cross channel at the top of the trunk floor that contains ventilation holes. Based on the mud splash pattern under the car I believe the rotating drive shaft is throwing water up into these ventilation holes. This water is then creeping down between the reinforcement plates and getting trapped. There is a second possible entry point on the sides of the plate which also have ventilation holes and may be taking in water from the rear tires; although when I cut out the top layer of reinforcement plates to investigate I noted the passenger side was much worse than the driver side - again I believe due to the rotating drive shaft.

 

Here is a picture (taken from where the fuel tank would be which I have removed at the moment).

 

Pathfinder Rust Spot 1.jpg

 

The preventative fix would be to shoot cavity wax into this area. I used Noxudol 750 which comes with a 360 degree 2' extension wand and has a high creep rate and anti-corrosion properties. After saturating the length of this channel very well with wax and waiting a bit - sure enough the wax started to drip out of the same areas that typically rust out between the plates.

 

Pathfinder Rust Spot 2.jpg

 

Another preventative may be to JB Weld some stand-off baffle plates over the ventilation holes (you don't want to plug the holes) which should stop any further water entry.

 

Lastly, a 3rd possible entry point are the lower rear seat belt bolts which penetrate the plates and into the rear wheel well. I didn't see as much evidence of this; however I removed these bolts, applied anti-seize and reinstalled them for good measure.

 

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Here is an interior pictures of the problem spots.

I carefully cut out only the top plate. The bottom reinforcement plates were still intact in my case so I put down anti-rust paint, fiberglass mat, aluminum body filler and patched it up which should be good enough - although I don't live in the rust belt.

 

Pathfinder Rust Spot 3.jpg

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Posted (edited)

I had no idea that section of the floor was double-walled! Makes sense, though--rust loves metal sandwiches, especially once dirt and moisture get in there.

 

I went and had a look at mine, and it doesn't have the hole in the middle, but it does have a couple of holes above each spring perch. My floor is solid so far (under the seats, at least), but I may copy what you've done with the wax to keep it that way. I'm tempted to try and find rubber bungs to fill those holes when I'm done. If the top is closed up, and the bottom is open enough to leak wax, surely that's enough ventilation, right? No sense leaving them open for stuff to get in that might not be able to get out.

 

I'm convinced that's what killed the frame on my '95--it's easier for dirt to get into the frame than it is for it to get out, so it just sits in there, clogs up the drains, and forms a wet (and salty, given where that truck was from) sponge up against the steel.

 

Edit: I looked up the wax spray you're using, and the Amazon link says it's "restorative scalp and hair care." :lol:

 

Edited by Slartibartfast
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24 minutes ago, Slartibartfast said:

I went and had a look at mine, and it doesn't have the hole in the middle, but it does have a couple of holes above each spring perch. My floor is solid so far (under the seats, at least), but I may copy what you've done with the wax to keep it that way. I'm tempted to try and find rubber bungs to fill those holes when I'm done. If the top is closed up, and the bottom is open enough to leak wax, surely that's enough ventilation, right? No sense leaving them open for stuff to get in that might not be able to get out.

 

 

That's interesting. I wonder if they attempted to partly fix the design issue it in later year models. If the center hole is not needed, then I will plug that one up at least.

On the passenger side, looking straight up through the hole there is a rust pattern directly above the hole which tells me the driveshaft is still throwing water directly up into this area. Maybe the center and pass side can be plugged and the driver side left open for breathing. I'm always cautious about plugging ventilation holes - you can never truly stop water ingress - you just have to let the car 'breathe'.

 

I went back and checked again today on the wax progress and it did eventually drip out of all of the seemed areas where this sandwiched plate ends.

 

28 minutes ago, Slartibartfast said:

I'm convinced that's what killed the frame on my '95--it's easier for dirt to get into the frame than it is for it to get out, so it just sits in there, clogs up the drains, and forms a wet (and salty, given where that truck was from) sponge up against the steel.

 

 

Yeah there is another design issue with the frame rust where the tires are. The rear tires spray water all over and inside the frame rusting it out. Other than also shooting cavity wax here I believe a proper fix would be custom gap guards which also cover the frame in this area which is what I plan to do.

 

34 minutes ago, Slartibartfast said:

Edit: I looked up the wax spray you're using, and the Amazon link says it's "restorative scalp and hair care." :lol:

 

 

hah. Here is a link. I prefer this brand because it's what the OEMs typically spec when they have rust related recalls. It has a high creep rate (like penetrant oil), anti-corrosion/conversion properties and doesn't wash away unlike many others.

 

https://www.noxudolusa.com/

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This is very interesting. I always had this issue on all my trucks, and even if you cut out the rot and welded new in, it would come back over a few years. Will be taking a look at mine when I replace the fuel tank in the coming weeks.

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Picture from the Body Repair Manual.

You can see the design issue where #17 is the channel with the water ingress (and where I injected wax) and the water/wax flows down between the two lower/sandwiched plates.

You should be able to get to the channel from in front of the diff it just might be tight especially without a body lift.

 

 

image.jpeg.484c20f2feddeec1f5d345df0cb3fb45.jpeg

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Posted (edited)
3 hours ago, FirstGenFreak said:

Do you all salt your roads over there in the US? 

I have never seen a WD21 with rust there in 20 years of messing with them. 

 

Yes, a number of northern states salt the roads.

 

wrt the rear seat rust issue, you won't see it until it's fairly severe because it's rusting from the inside out. You might be able to see evidence of the issue if you look under the car and see rust formation at the seams between the metal plates which would indicate water dripping out at the seams.

If you live in a dry climate it's just progressing much, much more slowly and may never reach the point of becoming a problem.

The car is actually fairly well built with the steel panels electroplated with a zinc-nickel alloy to protect the metal but nothing lasts forever...

 

Here's a pic when I was cutting out the damaged top plate on the pass side. Notice you don't see anything visible on the driver side (no rust showing through); however when I cut out the top plate it looked the same - severe rust hiding underneath.

 

Pathfinder Rust Spot 4.jpg

 

Edited by level9
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Some states use salt, some don't. The stuff eats cars for breakfast.

 

I need to get rid of my parts car soon-ish anyway, might have to drill out some spot welds and see how much trash it's collected between the layers.

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Posted (edited)

The salt up here means all but a handful are gone. I genuinely get excited when seeing another one on the road. Can go almost a year or more without seeing another wd21 here in Ontario. I have a couple friends that still have them. But we don't drive them in the winter. My current one originally came from Vancouver BC. Last one I saw in the junkyard in my town had to be almost 5 years ago at least.

Edited by adamzan
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They are definitely becoming a rarer sight over here, although rust really isn't a killer over here, they just aren't desirable in the same way a lot of older cars aren't. Car culture  (consumer culture?) isn't what it used to be either, it's easier to buy something new than it is to fix or maintain something older.

Parts are definitely drying up fast (at least body and trim parts) 

I have just bought a Dual Cab D22 as a daily driver as we have a 3 month old boy, and want room/access to rear seats and the wife wants me to get rid of the pathy. I am trying to put it onto historic registration which will make it almost free to own. Wish me luck!

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Good luck! I have mine on classic car insurance here, dropped it to about $250 CAD a year. Crazy cheap. I didn't register it with the province as historic as they put stupid restrictions on when and where you can drive it.

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