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What is a Torque Wrench and Why Your Toolbox Needs One

Torque wrenches are used to help you apply the recommended torque pressure to bolts, screws, or other fasteners. They reduce the potential of stripped bolts and damaged mechanical components.

What is a Torque Wrench?

The original torque wrench was invented by Conrad Bahr in 1918. It was designed initially to prevent the over-tightening of bolts that were installed on steam pipes and water mains used by the New York City Water Department. Today, the torque wrench comes in multiple forms, from manually operated to electrically controlled. They are used to apply the exact torque pressure to fasten a bolt, screw, or other fastener. A mechanic will review the recommended torque pressure settings for each component as required by the manufacturer. When used correctly, a torque wrench permits the perfect tension, assembly, and loading of all parts. It reduces the potential of stripped bolts, damaged mechanical components, and enhances safety.

Most automotive manufacturers recommend a specific torque pressure for individual systems that require a precision fit of force times distance – which is how torque is defined. Some of the most common automotive systems that require the use of a torque wrench include:

WHEELS

Anytime you remove a wheel from the hub, the lug nuts or bolts need to receive a final tightening via a torque wrench. Different manufacturers have unique torque settings, but generally – they range from 76 lb-ft on aluminum studs to 150 lb-ft for high-grade steel. *You can usually find the recommended torque pressure on the inside of the driver door on a placard that also lists the recommended tire air pressure.

SPARK PLUGS & CYLINDER HEAD COMPONENTS

The cylinder head is a precision fit piece of equipment – typically made of soft aluminum and requires a torque wrench to correctly secure components. The risk here is over-tightening by a pneumatic air wrench or manual wrench. When this occurs, the cylinder head components will warp, leading to excessive heat build-up, cracking, and eventually complete mechanical failure.

SUSPENSION & BRAKE SYSTEM PARTS

From calipers to struts and other suspension parts, every bolt or nut on a suspension and brake system should be torqued based on the manufacturer specs. If they are not torqued correctly, they can loosen since they move frequently. When this occurs, parts can break off the vehicle while in motion.

Why is it Important to Use a Torque Wrench?

If the nuts and bolts that secure a replacement part or mechanical system has a required torque pressure, a torque wrench is required for multiple reasons. In most cases, when we attempt to tighten fasteners with an impact wrench or manual wrench/ratchet – two things will happen.

FASTENERS WILL BE TOO LOOSE

If the fastener is too loose, it can create a gap between the nut or bolt, and the part it is securing. When this happens, excessive heat is built-up, which loosens the fastener to the point the bolt snaps or the part falls off. With wheels and steering/braking components, this can cause an accident and even fatalities.

FASTENERS WILL BE TOO TIGHT

Most DIY mechanics don’t realize how strong they are. In fact, over-tightening is more common than leaving fasteners too loose. When they are too tight, the danger comes in the form of too much force, which typically warps, bends or damages the bolts and the part itself.

General Torque Wrench Tips

Anytime you complete service on your car, truck, SUV or other vehicle, it’s always best to refer to a vehicle’s service and repair manual. This guide will not only provide you with steps for completing the routine service or parts replacement, but it will also give you the recommended torque pressure and torque pressure pattern. Here are a few general tips for using a torque wrench:

CLEAN ALL BOLTS AND FASTENERS BEFORE INSTALLATION

It’s always best to remove rust, dirt and debris from any fastener before you install. If you have excessive rust build-up, use a penetrating fluid like WD-40 to remove the rust. Make sure you remove excess WD-40 before installing the nuts or bolts.

SET THE TORQUE WRENCH TO THE RECOMMENDED PRESSURE

In the service manual you’ll see a recommended torque pressure. The bottom of the torque wrench has a series of numbers that indicate the pressure setting. Follow the torque wrench setting procedures as each torque wrench is unique and has different steps.

TIGHTEN COMPONENTS IN TWO STEPS

Guide the nut or bolt onto the part using a hand wrench until it is snug, but not tight. At this point, use a torque wrench by setting it to the recommended torque pressure. You’ll pull the torque wrench in tightening direction until you hear a “click” in the handle of the wrench. Stop at this point and tighten once more until you hear the “click” again.  The second click confirms your torque setting.

Whether you’re completing a simple brake pad replacement, swapping out steering components, or replacing spark plugs, always make sure to use a torque wrench for final tightening. If you don’t have one, AutoZone has several torque wrenches available through our Loan-A-Tool® program. Simply visit your local AutoZone and speak with our sales professionals, who will be happy to help.

Advice, how-to guides, and car care information featured on AutoZone.com and AutoZone Advice & How-To’s are presented as helpful resources for general maintenance and automotive repairs from a general perspective only and should be used at your own risk. Information is accurate and true to the best of AutoZone’s knowledge, however, there may be omissions, errors or mistakes.

Be sure to consult your owner’s manual, a repair guide, an AutoZoner at a store near you, or a licensed, professional mechanic for vehicle-specific repair information. Refer to the service manual for specific diagnostic, repair and tool information for your particular vehicle. Always chock your wheels prior to lifting a vehicle. Always disconnect the negative battery cable before servicing an electrical application on the vehicle to protect its electrical circuits in the event that a wire is accidentally pierced or grounded. Use caution when working with automotive batteries. Sulfuric acid is caustic and can burn clothing and skin or cause blindness. Always wear gloves and safety glasses and other personal protection equipment, and work in a well-ventilated area. Should electrolyte get on your body or clothing, neutralize it immediately with a solution of baking soda and water. Do not wear ties or loose clothing when working on your vehicle.

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