How To Use a Torque Wrench
While many automotive fasteners on your vehicle do not require accurate torquing, the critical components certainly do, such as suspension, engine, and drivetrain components. If you do not use a torque wrench, you probably are not getting those bolts tight enough, or in some cases, too tight. Both of which are really not good. Knowing how to use a torque wrench correctly is an important step in critical component assembly work.
The torque wrench was invented in 1918, interestingly to prevent underground water pipes from being overtightened. The original version was a beam-style wrench, which uses a pointer on scale to indicate torque application. Beam wrenches are accurate when taken care of and are still sold today, though they are more rudimentary than modern torque wrenches.
Torque Wrench Types
There are several types of torque wrench, including deflecting beam, slipper, click, hydraulic, electronic, and mechatronic wrenches. The most commonly used versions in automotive applications are the click and electronic, so we will focus on these.
Click style wrenches are what most of you will be familiar with. When you reach the desired torque rating, the internal mechanism clicks, letting you know that you have reached it. This is done with a precision calibrated clutch made from a ball and spring where the ball rests in a detent and when the torque head reaches a level that overcomes the spring, the ball pops out, making a “click”. The torque application does not stop, so you can over-torque if you don’t stop when you hear the click. These wrenches are set with a rotary ring on the handle. These wrenches are very affordable and when not abused, will remain accurate for many years. Most click style wrenches are noted in ft/lbs, but you can find them in inch/pounds, kg/M, Kg/cm and Newton/meter as well.
The modern version of the torque wrench is an electronic torque wrench. The electronic torque wrench you buy at your local NAPA Auto Parts Store uses an electronic sensor on a torsion rod to accurately measure applied torque. What is nice about these wrenches is that you get a warning as you approach the target torque, a beep when you reach it and even a digital readout of the actual applied torque. This means you know exactly how much the fastener has been torqued. The settings are adjusted through the digital readout with push buttons. One of the really nice features of a digital electronic torque wrench is the ability to change the scale, from inch/pounds to ft/pounds, kg/m, Kg/cm and Newton/m.
How To Use A Torque Wrench
Using a torque wrench is simple as long as you follow a few rules.
- NEVER use a torque wrench as a breaker bar. This will damage the calibration and ruin it. Torque can be applied in reverse for left-hand threads, but that is a different thing that breaking loose a fastener.
- ALWAYS set the wrench to the spec you want and stop when it beeps or clicks. Don’t estimate and don’t over torque your fasteners.
- NEVER take your torque wrench apart. Why would you even want to?
There are two different types of torque that you can measure with a torque wrench, clamping torque and rotational torque. While they are similar, they are not the same. Clamping torque is the final torque rating applied to a fastener, whereas rotational torque is the measurement of the force required to initiate movement and sustain movement, such as on the input yoke of a differential. Clamping torque is measured with any torque wrench, but rotational torque requires a beam or electronic torque wrench because you have to watch the dial to get the reading, where a click-style wrench only clicks when it is at a specific rate.
Rotational torque measurement is most often required for setting up a differential, specifically the pinion preload. This is usually measured in inch/pounds. A beam wrench is the best for this, as you get accurate readings without a lot of hassle.
One note about modern fasteners. Many vehicles are using torque-to-yield fasteners, particularly in engine components. These are NOT reusable and require a specific torquing procedure that includes torquing to a specific measurement and then tightening an additional amount, usually 1/4-1/2 turn. Make sure you know what you are working with, this is paramount for a successful job.
Ensuring that your critical fasteners are accurately torqued is, well, critical. Don’t guess when your life and others hang in the balance. If you think your steering linkage is correctly torqued and it isn’t, really bad things can happen. Don’t take the risk, get a torque wrench and use it.
Check out all the tools & equipment available on NAPA Online or trust one of our 16,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on how to use a torque wrench, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.