Greetings! (And 1990 HZJ73 Rust Repair Options)

[Rankle73]

Hello to the Mud community! Very recently purchased a triple-locked 1990 HZJ73 5MT during my stay here in Japan. While it only has just over 50000 km on the clock, and it appears to have been well-maintained by the PO, the past 36 years of Japanese weather has been rough on some of the common body rust points.

I'm familiar with @luigibella 's post covering rust remediation for the same model, but I wanted to ask about two options that have been proposed by local body shops. Admittedly, I was surprised by the estimates I received, but cheap labor and a weak Yen are on my side:

• Option A ($900): Cut out rusted sections and replace with fiberglass, then bondo and paint
• Option B ($1500): Cut out rusted sections and weld steel pieces from OEM body panels, then paint

I'm torn since while fiberglass would obviously alleviate the future rust issue at that location, I'd be concerned about moisture infil into the joint as well as longevity of the joint during regular shock/vibe. For Option B, welding in new sections would not prevent future rust, but perhaps I could fill in the sills where water/silt/salt collect to slow the process (any tips on this?). Curious to hear the community's thoughts, or if there's an Option C I can propose. Language barrier is a bit of an issue when dealing with these shops, unfortunately.

Here's the rusted spots—it's not too bad, yet, but it looked like the dealer or PO painted over mediocre body filler repairs right before selling it.

Location 1: LH rocker panel (aft)

Location 2: RH rocker panel (aft)

Location 3: LH rear quarter panel/wheel well/mud flap mount

For those interested, here's what I've done in the past month, most of which was done thanks to lurking here:

• All fluids (except PSF), including gearboxes
• Front brake pads
• RH door hinge (bushings were shot, and door was sagging) and latch
• Zip-tie repaired rear cargo door lock mechanism cam arm
• All door seals and weather stripping (window and windshield seals look good)
• "Custom" headlight warning buzzer
• Aftermarket keyless entry system
• Driveshaft/birf grease top-up (birfs still dry!)
• Serpentine belts
• Breathers cleaning
• Reflowed solder on temp/altimeter display
• Speedo cable clean/re-lube (was bouncing pretty bad)
• Trunk lip trim swap to plastic (due to rust), then re-seal
• Re-sealed taillight inner seams

And here's what's planned ahead:

• All suspension rubber parts/TREs
• PSF
• FRP top seal
• ARB compressor
• Breather extensions (x4)
• Manual hub lock conversion (attempted to replace brushes in INOP LH hub, but this did not work—OEM electric hubs are currently manually activated)

Thank you in advance!

 

[JuanJ]

Hello,

Welcome to the madness.

Those are common rust spots on JDM trucks.

Bondo and fiberglass trap air and most.

Cutting and welding may require revisiting in the future but proper preparation and coatings can delay the process long enough. Some body panels are still available, and it would be wise to get them.






Juan

 

[Rankle73]

Hello,

Welcome to the madness.

Those are common rust spots on JDM trucks.

Bondo and fiberglass trap air and most.

Cutting and welding may require revisiting in the future but proper preparation and coatings can delay the process long enough. Some body panels are still available, and it would be wise to get them.






Juan

Got it, thanks! It somewhat pains me to buy a whole panel to just cut off a small piece of the rocker section, but it's nice to have them readily available.

Any recommendations for filling in the sill areas at the inner bottom of the body panels to prevent moisture from accumulating? I guess the flip side is that any solution might trap moisture in there, as well.

 

[JuanJ]

Got it, thanks! It somewhat pains me to buy a whole panel to just cut off a small piece of the rocker section, but it's nice to have them readily available.

Any recommendations for filling in the sill areas at the inner bottom of the body panels to prevent moisture from accumulating? I guess the flip side is that any solution might trap moisture in there, as well.

Hello,

Rust begins with small pieces and then grows.

You can cut the area around the rust hole and patch it with new metal. If properly done, this repair will hold for a while.

The spot where the sill joins the body has two drain holes. If you keep them clean, moisture and water will drain off.

Ideally, you want to fill body and frame inner spaces with cavity wax or a similar product to keep water away, especially during winter.





Juan

 

[Rankle73]

Hello,

Rust begins with small pieces and then grows.

You can cut the area around the rust hole and patch it with new metal. If properly done, this repair will hold for a while.

The spot where the sill joins the body has two drain holes. If you keep them clean, moisture and water will drain off.

Ideally, you want to fill body and frame inner spaces with cavity wax or a similar product to keep water away, especially during winter.





Juan

Juan, thank you very much for the tips, I’ll have to look more into the cavity wax. Cheers!

 

[Felde]

Hi
Nice truck.
If you want to keep the vehicle: Weld in steel and do a proper rust conservation. If welded in correctly, it's almost as good as original.
Fiberglass & Bondo will not hold up: Moisture trapping and different material characteristics under heat, rain and vibration will take its toll.
My 3 cents.
Good luck Ralf

 

[fullthrottle]

Ahhhh, welcome to the 80's JDM rustang workshop


Currently restoring the body on my BJ73. Definately patch with steel. Electro galv would be best. Just grind off the galv spots where you will weld.
Any panels your replacing, paint the insides before your seal them up.

Once sealed, and to ensure those welded spots don't rust again, you could try my method....
Sparying Dinitrol ML inside the panel. This stuff really gets into every nook and cranny. Once that's dried off a but, I overlay with Dinitrol 1000.
You can make up a flexible hose with multiple holes that attaches to the applicator gun. This was it will spray all around everything...just like a psyhco hose beast

Difference between ML and 1000

Good luck

 

[Rankle73]

Hi
Nice truck.
If you want to keep the vehicle: Weld in steel and do a proper rust conservation. If welded in correctly, it's almost as good as original.
Fiberglass & Bondo will not hold up: Moisture trapping and different material characteristics under heat, rain and vibration will take its toll.
My 3 cents.
Good luck Ralf

Ahhhh, welcome to the 80's JDM rustang workshop


Currently restoring the body on my BJ73. Definately patch with steel. Electro galv would be best. Just grind off the galv spots where you will weld.
Any panels your replacing, paint the insides before your seal them up.

Once sealed, and to ensure those welded spots don't rust again, you could try my method....
Sparying Dinitrol ML inside the panel. This stuff really gets into every nook and cranny. Once that's dried off a but, I overlay with Dinitrol 1000.
You can make up a flexible hose with multiple holes that attaches to the applicator gun. This was it will spray all around everything...just like a psyhco hose beast

Difference between ML and 1000

Good luck

Amazing, thank you! I think I'll go with the shop charging $1500 all-in to fix the three spots as I'm neither a good welder nor grinder. Will also look into sourcing the cavity waxes here once everything is done.

Is it worth having someone laser off all the existing underbody coating that's starting to flake off, then coating everything with that wax (or Fluid Film?)? Appears to be a black paint-like coating (not rhinoliner-type). Overall, the underbody is in pretty good shape considering 36 prior years in Japan.

More photos for reference—will be taking care of suspension bushings this weekend.

 

[Felde]

Hi
The frame outside should be painted. No underbody coating. Wax may go over the paint, but imho it's not ideal for offroad rigs as all dirt & dust sticks to it, and it will not hold up pressure washing for long.
FluidFilm is a penetrating conservant great for cavities and overlapping sheets as well as for temporary conservation e.g. against salt in winter, but it is also not a permanent coating.

Not a lot of the frame to see in the pics, but overall doesn’t look too bad to me.
I'd do an intense pressure wash and mild brushing o get off any loose matter and then do an assessment.
What's that foamy stuff on the oilpan? Never saw something like this.
Cheers Ralf

 

[Rankle73]

Hi
The frame outside should be painted. No underbody coating. Wax may go over the paint, but imho it's not ideal for offroad rigs as all dirt & dust sticks to it, and it will not hold up pressure washing for long.
FluidFilm is a penetrating conservant great for cavities and overlapping sheets as well as for temporary conservation e.g. against salt in winter, but it is also not a permanent coating.

Not a lot of the frame to see in the pics, but overall doesn’t look too bad to me.
I'd do an intense pressure wash and mild brushing o get off any loose matter and then do an assessment.
What's that foamy stuff on the oilpan? Never saw something like this.
Cheers Ralf

Ok sounds great, will look into all of that. The original underbody paint seems to have protected most things well but it’s starting to peel everywhere.

And I assume you’re asking about the oil/grease/dirt sponge, AKA oil pan insulator: https://www.amayama.com/en/part/toyota/1215617010

Mechanically, she’s quite sound with just over 50000 on the clock, timing belt was surprisingly changed 10 years/20000 km ago due to age, and the belt and tensioner appear to be in good shape (I did buy a replacement but haven’t found the time). The hoses I’ve inspected have all been good as well.

 

[fullthrottle]

Agree with the above. The cavitiy wax based products (Dinitrol ML and 1000) are only for places that won't see the light of day again. Not a permanent external coating.
Clean it up, scrape off the loose stuff and see what it's like.
If just a bit of light surface rust, clean/sand/grind it off as much as possible. Coat is with some rust converter. I've been using Brunox as it's a converter and expoxy in one.
Then your top coat of choice. I've used a 2k primer the 2k black top coat for the chassis. Similar for the under body, but the final coat is Dinitrol 447.