that’s likely where the rust begins.
Many trucks of this era may have had a camper shell on them, and some of those have used a rubber gasket between the shell and the cab. If so, they may have a telltale rust line outside the normal boundaries of the rear window. (Photo Courtesy Lonnie Thompson)
If the body part has an area that you can move for more access, open it. The tailgate, for example, may have rust in the lower corners near the hinges. Open the tailgate and take a look, pulling it away from the body if possible. Open the doors and inspect both sides of the door skin, plus the bottom of the door itself. Look behind the rocker panels and the lower areas of the bed. Just because rust is not obvious on the outside, doesn’t mean that it’s not on the inside.
The bottom of the cab is a bit more difficult. Assuming that the truck is stock height, stick your head underneath and look for areas that are red in color. There may or may not be bubbles in the finish, as some regions used rust proofing on their vehicles right off the dealership lot.
The cab corner on this truck is obviously damaged and needs to be replaced. But how about the rocker just forward of it? In this case, it seemed fine, but it’s always good to look for damage if adjacent panels have issues as well. (Photo Courtesy Jefferson Bryant)
Rust on the cab floor is usually hidden on the inside by carpet, but you should be able to see any obvious patch panels or repairs from previous jobs. If the welds look like peanut butter or the work looks sloppy, prepare your offer accordingly.
The bed is another spot where rust can rear its ugly head. In the early years, Chevrolet had some problems with premature rust, which, depending on your source, was either from poor metal choices or a faulty primer. This rust showed up on the fenders as well, as both the bed sides and the fenders used the same materials. This was mainly a problem in the early years of 1973–1975, but depending on the truck, you may find it in later models. To know if these trucks have the bed sides that were replaced early on, look for the color of the primer on the inside of the bed; gray is the original primer color, and black is for the replacements from the recall. Some also have obvious patch panels.
Now, rust isn’t a deal breaker. It’s likely that you will find it no matter where your truck has lived during the previous few decades. Finding excessive rust is when you realize that you’re going to have to replace more than 50 percent of the sheet metal, and it could be worse than that. The first rule with rust is to always assume there’s at least 20 percent more of it than you can see; it might be lurking under paint and bodywork.
That 50-percent number may seem low, as you may enjoy or have experience doing metal repair. To others, that may seem too high because they don’t want to do any metal work if they can avoid it. It all comes down to experience. Just know that you need to keep that other 20-percent figure in your head because you always find more rust than you expected.
You can take your truck to an ASE-certified mechanic, have him conduct an inspection, and uncover any problems. He can hook the truck up to a scope and identify any readily apparent problems. At a bare minimum, you should take your Squarebody on a test drive to evaluate the current condition of the engine and drivetrain. Drive it around the block a few times before you hit the freeway.
Does it sound like it’s misfiring? Can you smell excessive amounts of gas? Does it blow out white, blue, or black smoke? White smoke indicates coolant in the oil. Blue smoke often means that it has worn valve seals and seats. Black smoke is a telltale sign that the fuel injection or carburetor is not correctly calibrated. Each one of these questions helps you determine whether or not the engine is worth keeping or if it needs some work.
The same goes for the transmission. If each automatic shift feels clunky and it sometimes misses a gear, that transmission needs to be inspected thoroughly. If it’s a manual and the clutch barely grips and it grinds into every gear, it also needs work.
It’s difficult to know if you have a cracked block, but one very basic test is to try to turn the crankshaft. Using a long-handled ratchet and socket, turn the crankshaft bolt (in the centerline of the engine, toward the bottom) to move the pistons. If they move, it’s a good sign. If they don’t, or if they require a serious amount of force to get moving, there are likely other issues, such as a seized piston, bent pushrod(s), bent crank, and so on. No matter what they are, it’s likely that the engine is pretty well damaged, so you might want to consider it a wash. Worst case is that you have to buy a new engine; best case is that it needs a mild rebuild.
Performing a leak-down test and a compression test are two other ways to determine the condition of an engine. A leak-down test is used to test pressure retention on each cylinder. Two- and single-gauge models are available, but for more accurate results, use a two-gauge type.
With the engine warmed up and turned off, remove the spark plug on the cylinder that you’re testing. Turn the engine over to top dead center (TDC), using a ratchet on the crankshaft, and put the air fitting adapter into the spark plug hole. With the gauge at zero, connect the air line from your air compressor to the other end of the tool. Now check the gauge to see how much air is leaking. If the number is between 8 and 12 percent, you’re fine; the engine should be great. Test the rest of the cylinders; a variance of up to 5 percent among them is acceptable. If the numbers are between 15 and 20 percent, it’s time to figure out where the leak is coming from.
With air pressure in the engine, listen to see if you can determine the source of the leak. If it’s coming out around the dipstick tube or valvecover breather, it’s leaking past the rings. If it’s out of the carb, it’s past the intake valves. If it’s leaking out of the exhaust valve, you may hear the noise anywhere in the exhaust, including the tailpipe.
If the leakage number is higher than 20 percent and it’s past the rings, it’s time to move on. The engine needs some work, and although it’s drivable, you may experience some horsepower loss. If the leakage number is more than 30 percent at the exhaust valves, pass on the engine. If it’s more than 20 percent on the intake valve, you’re there as well. Granted, these aren’t hard and fast numbers, and the decision is ultimately up to you. But consider your options.
A compression test is similar to a leak-down test, but it uses an older technique. Remove all of the spark plugs and then pop the coil lead off the coil. Connect a compression tester to a spark plug hole. Crank over the engine using the key and starter, and count how many engine revolutions it takes for the gauge to top out at maximum pressure (you may want to have a helper turn the key while you check the gauge). Do this for every cylinder, taking notes along the way, until they’re all checked.
You’re looking for consistent pressure in each cylinder, and to ensure that the numbers are within 10 percent of one another, give or take. If your gauge reads less than 30 percent, the engine has a compression leak, and you may want to move on (or negotiate the price of the truck lower accordingly).
If you’re not good at these types of mechanical projects, consider paying a professional mechanic to give the truck a once-over. Many mechanics can check out a project for you on the side, depending on the price you offer. If you don’t know or trust any mechanics (or you don’t have the extra cash), maybe one of your experienced friends could do it. Either way, it’s always good to have a second opinion, particularly if he or she has more experience than you do.
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