How To Use a Torque Wrench

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.

The beam style torque wrench is useful, but it does not tell you when you have reached your target. The best use for these wrenches in is measuring rotational force, such as when setting up a rear differential.

The beam style torque wrench is useful, but it does not tell you when you have reached your target. The best use for these wrenches in is measuring rotational force, such as when setting up a rear differential.

 

Small inch-pound wrenches like this are usually 1/4" drive, so you need an <a href="https://www.napaonline.com/en/p/BK_7741467?cid=social_blog_042018_torque_wrench" target="_blank" rel="noopener">adapter</a> to go to 1/2" for big stuff like pinion nuts.

Small inch-pound wrenches like this are usually 1/4″ drive, so you need an adapter to go to 1/2″ for big stuff like pinion nuts.

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.

The most common style of torque wrench are the mechanical clicker, and the electronic wrench. they both have advantages and disadvantages.

The most common style of torque wrench are the mechanical clicker, and the electronic wrench. they both have advantages and disadvantages.

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.

Mechanical wrenches use a rotational setting guide to adjust the torque setting. This is much like a micrometer, when you go to the 40-pound range on the shaft and then spin the collar to "6" for total of 46 foot pounds.

Mechanical wrenches use a rotational setting guide to adjust the torque setting. This is much like a micrometer, when you go to the 40-pound range on the shaft and then spin the collar to “6” for total of 46 foot pounds.

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.

The nice thing about electronic wrenches is that they can be adjusted for foot pounds, inch pounds, and newtons.

The nice thing about electronic wrenches is that they can be adjusted for foot pounds, inch pounds, and newtons.

 

The downsides of the electronic torque wrench are two fold. First it requires batteries, and if you don't have replacements when you need it, it won't work. Second is that some have plastic parts on them that can break like ours did if you aren't careful. It has worked fine like this for years, but something to keep in mind.

The downsides of the electronic torque wrench are two fold. First it requires batteries, and if you don’t have replacements when you need it, it won’t work. Second is that some have plastic parts on them that can break like ours did if you aren’t careful. It has worked fine like this for years, but something to keep in mind.

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.

Measuring rotational force requires either an electric or beam wrench. The wrench must meet the specs, so a specific wrench for that task is usually used like this inch-pound wrench that reads from 0 to 60 inch points. A generic use electronic wrench usually does not go that low.

Measuring rotational force requires either an electric or beam wrench. The wrench must meet the specs, so a specific wrench for that task is usually used like this inch-pound wrench that reads from 0 to 60 inch points. A generic use electronic wrench usually does not go that low.

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.

Torque specs vary greatly by manufacturer, you need to be careful. Most modern vehicles use torque to yield bolts which are not reusable. They are torqued to a certain spec, then turned an additional 1/4 or 1/2 turn to yield the proper bolt stretch.

Torque specs vary greatly by manufacturer, you need to be careful. Most modern vehicles use torque to yield bolts which are not reusable. They are torqued to a certain spec, then turned an additional 1/4 or 1/2 turn to yield the proper bolt stretch.

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.

about author

Jefferson Bryant

A life-long gearhead, Jefferson Bryant spends more time in the shop than anywhere else. His career began in the car audio industry as a shop manager, eventually working his way into a position at Rockford Fosgate as a product designer. In 2003, he began writing tech articles for magazines, and has been working as an automotive journalist ever since. His work has been featured in Car Craft, Hot Rod, Rod & Custom, Truckin’, Mopar Muscle, and many more. Jefferson has also written 4 books and produced countless videos. Jefferson operates Red Dirt Rodz, his personal garage studio, where all of his magazine articles and tech videos are produced.

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