A lot of buyers look at the surface-level problems they can see with their own eyes. The serious structural damage usually hides behind the panels and inside the hollow box sections of the frame. What looks like a pretty manageable restoration project can balloon into a $15,000 rebuild once disassembly starts and all that hidden rot finally shows up.
The 240Z was released in the early 1970s, and Nissan cared far more about how it looked than about rust prevention. The factory rust protection on these cars was minimal at best. The body design has dozens and dozens of small pockets and crevices where water can work its way inside, but has no way to escape. Rust eats through the metal from the inside out, and the exterior paint can still look decent enough to convince you that you've found a clean example. Cars that feel sturdy can still hide serious rust damage in the frame rails, the floor transitions and the door structures - and these repairs are going to hurt your safety and your wallet.
The hidden places are what separate a successful restoration from a very expensive mistake! Most failed 240Z projects don't actually fail because of the rust you can see on the surface - they fail because buyers didn't check the right areas before they bought the car. I'm going to talk about the main hidden zones where the worst rust tends to develop and show you how to check each one before you buy. Skip these checks, and you might find yourself with an affordable project car that needs frame-off metalwork that costs more than the finished car would ever be worth.
Let's go over the sneaky places where rust loves to hide on these classic cars!
Table of Contents
Frame Rails That Hold Your Car Together
Frame rails should be at the top of your inspection list for any 240Z because these parts are what hold the entire structure of the car together. Every 240Z has a pair of front frame rails that run right behind the radiator support, and then a set of rear rails back where the differential mounts up. Rust is a concern in these areas, and the tough part about frame rail corrosion is that it tends to start on the inside, where you can't see it. Over time, it works its way through the metal until it finally shows up on the outside.
Frame rail damage hides very well because rust works from the inside out, and this creates problems for anyone who tries to check a vehicle. The outer metal surface can look perfectly fine even when the interior has deteriorated. You'll get false confidence if you just look at it - everything looks solid and sturdy on the surface. A quick tap test with a small hammer will show you what's actually going on, though. Instead of that reassuring thunk you'd expect from healthy steel, a compromised frame rail produces a hollow, tinny sound.
A hammer tap test is one of the most reliable ways to check for frame rail problems. You should walk along each rail and tap it gently with a hammer every few inches or so. The sound it makes is what matters here. A healthy frame rail will give you a sharp, almost musical ring if you tap on it. Metal that's been compromised by rust is going to sound different - dull, hollow and empty. The contrast between the two sounds will tell you everything you need to know about the condition of that rail.
Frame rail replacement is one of the most expensive repairs that you might run into with a 240Z. You'll cut out the old, rotted metal and then weld in new sections to replace it. It's definitely not a cheap fix. Labor costs alone will usually run you a few thousand dollars at a minimum because this work takes a skilled welder and time to get it done right.
Some project cars just aren't worth saving when the frame rails have rusted too far. You'll have to be honest with yourself about the condition before jumping into a restoration. A car with corroded frame rails can look like a decent deal at a low price. Start tallying up what it would actually cost to fix everything, and the numbers get out of hand fast. In a lot of cases, the total repair bill ends up being more compared to what the finished car would ever be worth.
Check each side of the rail closely and compare what you see. One bad rail is a cause for concern. But two bad rails mean you should walk away from the car altogether.
Hidden Damage from Battery Tray Rust
Rust loves to attack cars in all sorts of places. But the battery tray has to be the worst place for it to take hold. Battery acid drips down from the terminals, moisture collects underneath with no way out, and the rust just eats through that metal way faster than it does on the rest of the chassis. It's nearly impossible to keep this area dry because batteries release corrosive vapors all the time whenever they're in use or get charged.
Surface rust on the battery tray shows you the start of a much bigger problem. Once it starts, it spreads pretty fast to the inner fender, and from there it makes its way to the firewall junction. All these panels are connected and share the same pocket of trapped moisture and acid residue. The tray itself might not look that bad from the outside. But the damage happens where it mounts to everything around it, and that's what you'll have to check.
Most of the worst damage actually happens behind the battery tray in a place hard to see without taking some parts apart first. The structural supports back there keep the front end held together and help to distribute the weight and stress evenly across the whole chassis. Once rust gets into those supports, you're going to start having stability problems that affect how the car drives and whether the front suspension mounts can stay in place.
You might see a rusty battery tray and think you can just patch that corroded area with new sheet metal. But rust almost never stays on the surface. Once corrosion works its way into a battery tray, it spreads through the metal and weakens the structure around it. It's not a situation where you can get away with a quick patch job. You're almost definitely going to need full metal fabrication work to restore it properly.
The rust in this area can hide plenty of damage underneath it, so you should take a close look at whatever surface rust you can see. Grab a flashlight and point it into the places where the inner fender meets up with the firewall. Take a screwdriver and press it against the metal to test for any weak points. If the metal starts to flake off or crumble after you apply just a little bit of pressure, that section needs to be replaced - there's no way to repair it and have it hold up right.
Problem Areas That Cause Floor Damage
Water has a way of finding its path inside through old door seals that have worn out over time, and when it does, the driver's footwell is usually where it ends up collecting. Plenty of car owners will check the carpet, see that the surface looks dry and in one piece and believe that the metal underneath is fine too.
Get down there and press hard on the carpeted sections with either your hand or your foot to feel for any give in the metal underneath. When it feels soft or spongy at all, that's a sign that the metal has already started to thin out or that holes could start to form. Look at where the floor pan meets up with the transmission tunnel. Water loves to pool in these little corners and just sit there, and these areas usually get the worst of the moisture damage.
The places where your floor pan meets the firewall and rocker panels are even worse. The metal folds and overlaps in these areas create small pockets, and these pockets hold moisture perfectly. Rust spreads much faster here than it would on a basic flat section of your floor pan. Once rust works its way into these folded seams and transitions, you're looking at repairs that are much harder than just a cut-and-patch job on a basic hole in a flat area.
Pull back the floor mats and any loose carpet so you can get a look at the bare metal underneath. Take a close look at the welds and seams where the different panels meet up. Surface rust you can handle. Flaking metal or small holes around these seam areas mean that the repair is about to get a lot more complicated fast. A floor pan replacement takes skill to get all these transitions lined up just right!
Check Your Door Frame and A-Pillar Areas
Door frames should be your next inspection point after you've gone over the floor pans. The bottom corners of the frames and the base sections of the A-posts need careful examination because these areas tend to trap moisture. Water finds its way into the hollow sections of the frame, and once it gets in there, it ends up trapped with no way to drain away.
Damage isn't always visible from the outside. Rust tends to eat away at these parts from the inside out and makes it hard to detect early on. An endoscope or inspection mirror can help with this - these tools let you get access to those door frame channels that are otherwise impossible to see well. You'll need a decent flashlight for this inspection, and it's worth the time to look around in there for any signs that the metal has started to deteriorate.
After rust gets into these areas, it changes the way that your doors line up with the body. The bigger issue is what this does to your vehicle's safety. These panels help protect your car in a crash, and when the metal gets weakened by the rust, it can't do its job to protect you and your passengers in an accident.
Repairs in these areas get expensive very quickly. A qualified mechanic is going to need to weld fresh metal into the door frames and A-posts, and this work takes plenty of skill and patience to get it right. The person who does the repair has to maintain the structural integrity and the original shape of the frame at the same time. A quick patch job just won't cut it when you work on something that matters this much.
This part of the inspection deserves some time and attention, so don't rush through it. You'll need a small mirror and a decent light source, and you should run your fingers along the inside edges wherever you can reach - you're feeling for any soft areas or holes. If the seller starts to get impatient as you check everything over, well, that alone should tell you something about what you're looking at.
Check Your Rear Hatch and Spare Well
The rear hatch area deserves attention, mainly because water loves to pool up back there and cause damage that can stay hidden for quite a while. The rain gutters run around the perimeter of the hatch to channel water down and away into the spare tire well. After years of normal use and driving, rust eventually starts to form at the bottom of the well and then slowly works its way up into the corners over time.
You'll need to remove the spare first and check the bare metal underneath to see what's going on down in that spare tire well. Sound-deadening material can sometimes be found in there, too. Make sure to pull it out when you find any - rust has a nasty habit of growing right underneath those layers in places where it's invisible. After you've removed everything and cleared it all out, the bottom surface might look just fine sitting there. To make sure, apply some gentle pressure with your hand and feel around for any soft areas that are a telltale sign that rust has been eating through the metal from the other side.
Another area worth checking is where the rear window frame meets the body. Water can work its way into this seam pretty easily, and once it's trapped in there, it stays wet and doesn't dry out like it should. After enough time passes, rust holes will start to form and eat away at the structure that surrounds the window.
The hatch needs strong mounting points to support its weight, and those points need to be in decent shape for everything to open and close the way that it should. Rust will slowly eat through the metal around those mounting points over time, and once that happens, the hatch is going to start sagging or moving out of where it's supposed to be. Gaps that didn't show up before might start to form, or the latch won't catch quite right anymore.
Don't rush through this inspection, because repairs to the rear section can get expensive pretty fast. When the damage in the spare tire well is bad enough, you're typically going to need patch panels or maybe even a full replacement of it. Window frame rust is even more of a problem - it takes skilled metalwork and a careful hand to restore the frame and get it back to where it's structurally sound again.
Build Your Dream Car
Check these hidden areas before you hand over your money - it can make the difference between a solid buy and a money pit that'll drain your wallet for years. Surface rust on a rocker panel or some bubbling paint looks pretty bad at first. You can usually fix it without a massive bill, though. Structural rust in multiple hidden places is a whole different problem - repair costs can climb way higher compared to what the car is even worth. How well you check these less obvious areas before you buy will decide if you walk away with a sound shell or wind up with a rusty mess.
Clean 240Z shells are still out there. You can find one if you have a bit of patience and the discipline to walk away from anything that doesn't cut it. A decent flashlight, a small mirror and maybe a friend who knows these cars inside and out will find far more problems during your inspection than you'd find on your own.
Once you have a sound shell, the next step is to find the right parts to build it up into what you want. At Skillard, we make custom parts for the 240Z, 260Z, 280Z and other Datsun models. You'll find options that'll work for your project, whether you're after targeted upgrades or more of a build. Our catalog includes bumpers, aluminum door cards, center consoles, spoilers and other parts - they're built with an attention to quality and innovation for Datsun enthusiasts who want their cars to look great and perform well.
Check out Skillard.com to browse the full parts lineup and turn that shell into the car that you've been planning.
