1. Let's say it's time to replace the shocks. The job really isn't that tough or inherently dangerous. But it does involve getting your car up in the air so you can work underneath it. And that's where things can get troublesome—quickly. Your nifty new floor jack makes short work of putting another foot of daylight between the bottom of the car and your driveway. And two short stacks of stout cement blocks will be amply strong to hold it there. The car will be plenty stable, because those blocks have a wide footprint. Right?
You've already broken the lug nuts loose while the car was still on terra firma and removed the wheels. So you casually close the door to turn off that annoying buzzer. That sends a vibration through the chassis and causes a big, big problem.
In the blink of an eye, the front end slides right off the jack and every single one of those four cement blocks returns to its sand-and-gravel ancestry, leaving your poor car perched on four naked brake discs.
Imagine, just imagine, if you were under the car, wrench in hand, when this happened. Ouch!
Lessons LearnedWorking on your own car can be easy and fun, but it's got some potential dangers if you don't use common sense. The most obvious example we just played out: Wrenching underneath a car is a good way to become two-dimensional if you don't take the proper precautions. Let's catalog some procedures.
The only appropriate place to jack up a car is on pavement. And in our case pavement means concrete, not softer asphalt. A jack stand can make a nice cookie-cutter hole in thin asphalt. And that's especially true on a hot day, when the sun has made asphalt the consistency of molasses. Speaking of stands—always use ‘em, folks. Concrete block is not acceptable, because it's far too frangible. There are really only three options: ramps, old-school jack stands and, of course, a hydraulic lift. Ramps are great if you just need to change the oil. But for suspension or brake work, you'll need to remove the wheels and get into the wheel well. That means jack stands. They're not expensive, so splurge and get a pair that's rated for your largest vehicle.
What about wood—say that big stump over in the corner of the yard? Again, it's possible for wood to crack and separate under stress. I recommend wood to protect the bottom of a sheetmetal pinch weld or chassis component while a vehicle is being lifted. And wood is good for other stuff too. Scrap 2 x 4s are certainly fine for blocking wheels to keep the car from rolling off the stands. That reminds me: Don't trust the parking brake or the parking pawl in the transmission when you're working under a vehicle. A friend of mine learned that the hard way one day while changing the U-joints on his pickup. He'd left the truck in park and didn't bother to block the wheels. As he removed the last bolt from the differential flange, the truck rolled right over him, down the driveway and into the ditch across the street. Then he had to crawl under the truck and, lying in muddy water, reinstall the driveshaft so he could drive out of the ditch. Embarrassing, yes. But potentially deadly, too, if his truck hadn't been so tall it rolled completely over him. Not to mention the truck rolling into traffic.
It's just a quick fix, you say, so why not use a floor jack? No sir. A floor jack is not safe to support a car by itself. The hydraulic pressure inside the jack's slave cylinder is what's holding up that car. If any one of those rubber seals inside fails, the jack can dump pressure in a real hurry. And let's not even consider the possibility that Saturday Mechanic Jr. might wander into the garage and try to "help" Daddy by twisting the jack handle. It's happened, dude. Trust me.2. Upsy-Daisy Here's how to raise a car or truck safely. Find a level, flat piece of pavement, and break the lug nuts loose before you do anything else. If you're using the stock scissors jack that came with your car, you're probably stuck working on only one corner at a time. But that's really the safest procedure, anyway. Lift from the factory-recommended jack points, which you can find in the glove box, on a placard or with the jack and tools. With the car well up in the air, put a stand under a beefy suspension part or frame rail. And to be clear, "beefy" does not mean things like the radiator supports, the exhaust system, the sway-bar mounts or the sheetmetal floor pan. Lower the car onto the safety stand, but leave some of the weight on the jack. Shake the car to see that it's stable. Then shake it again with some muscle, just to be sure.
Now you're thinking you've got the car safely lifted, right? Wrong. I've got one more trick. Remove the tire and wheel, and place it under the car, somewhere in the vicinity of where you'll be working. If your head is roughly the same size as mine, it's no thicker than that wheel, so in the unlikely event of a water landing (oops, wrong speech)—so if the car comes sliding off the jack, your wife won't be cashing in your life insurance policy.
The same principles apply when using a floor jack. The floor jack will allow you to lift one end of the car, not just a single corner like that scissors jack. Your best bet is to jack from the middle of the chassis on the front subframe or transmission case or from the rear differential housing. And just so we're clear, the oil pan, exhaust system or gas tank isn't a safe jacking point. If you don't recognize these items when you look at the bottom of your car, you probably shouldn't be under there, and you don't need to read any further.
Remember, when the floor jack goes up and down, the jack pad describes an arc. The jack's wheels need to be free to roll as the pad moves on its arc or the pad will slip. Ditto for later, when you're using the jack to lower the car. Even a pebble can keep those small metal wheels from rolling.3. Underhood Work Not all the perils of auto maintenance happen underneath the chassis. There's plenty of danger under the hood, too. Aside from the obvious stuff, like sticking your fingers into the fan or belt when the engine is running, there are other ways to seriously hurt yourself under there.
If your vehicle has an electric cooling fan, be aware that it can spin all by itself, even when the key has been turned off. These fans continue to cool the engine until the block has dissipated most of its heat. And that could mean 15 minutes on a hot day. Pull the fuse or relay if you must work near it and just can't wait.
The radiator cap is another danger zone. It keeps coolant under as much as 15 psi and at temperatures as high as 230 F. The high pressure raises the boiling point of the coolant well above its atmospheric boiling point. Crack open the cap and it can flash-boil as the pressure in the system plummets. It's best to wait until the pressure drops back to zero. You'll know, because the upper radiator hose will be lukewarm to the touch and will feel squishy. If you must open the cap, use a rag and crack it open to vent—be sure to keep clear of the live steam. You might not even be able to see that steam, either, so use extreme caution. You had better have a good reason for opening the system anyway, because all the coolant that turns to steam or boils out will have to be replaced.
Fuel lines are another trouble spot. Sure, you've bled off the pressure (which could be as high as 60 psi, enough to squirt gasoline all the way across the shop) at the Schrader valve on the fuel rail, or by cranking the engine with the ignition disabled. But there is still fuel in that line. And if you're doing electrical work nearby, a few spilled drops from that line could catch fire.
One anecdote: I was working on a VW a few years back and disconnected the fuel lines so I could unbolt the cylinder head. Unbeknownst to me, VW has a cute strategy to help its cars start promptly. To fill and pressurize the fuel lines between the in-tank pump and the engine, the fuel pump runs for a few seconds when you open the driver's door.
Yes, I opened the door and sprayed gas right into the face of a gentleman standing close by. No lawsuits, but rest assured, I always clamp off fuel lines whenever I've got them disconnected. And no smoking—please.
Not all of the work around the shop is on the car. Plan to fire up the welder to tack the metal lawn furniture back together after a rowdy Super Bowl party? Let's remember to police the area near the welder or the grinder. Be sure to remove that pile of shop rags and last week's newspaper. You do have a fire extinguisher in the shop, right? I've extinguished two fires in my life, one my own fault, the other someone else's. They both would have been ugly had I not had an extinguisher. In fact, one would have cost me a Porsche 356 Carrera (serial no. 007) if there hadn't been a $15 Firebottle nearby. Thank goodness.