What is a Torque Wrench and Why Your Toolbox Needs One

Suggested AutoZone Products

Torque Wrench

Buy Now

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, including both manually operated and electrically controlled versions. 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. While any and every avid mechanic has a torque wrench, or several in their arsenal – there is a need for the torque wrench in every DIYer’s tool box. 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. This by far is the #1 use for all DIYers to have a torque wrench in their tools. 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, but generally, most vehicles wheel nut torque is between 80-95 lb-ft.

*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.

ENGINE COMPONENTS

A vehicle’s engine is composed of a multitude of precision-fit parts. From the cylinder head and intake manifold, all the way down to connecting rod and main bearings, everything has an exact torque specification. The risk here is not just over- or under-tightening, but making sure there is perfect consistency across each fastener, like a cylinder head, that often has 10-20 bolts securing it down, and clamping the important head gasket between it and the engine block. When inconsistency between fasteners occur, 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 to wheel hub nuts, 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 fail while the vehicle is 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 a 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 wire brush to completely clean the fastener’s threads. Use a thread chaser to clean a bolt hole, especially if rust or baked on grease is present. This is especially important on engine components. Many engine component bolts require lubing either the threads, or the bolt head with engine oil or a dab of grease before torquing. Consult your car’s manual to check if this applies to the bolts you are torquing!

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.