I'd like to take some time to discuss torque. As a young man, many hours were focused on torque as it related to horsepower at the local dragstrip. It was never applied on the streets [fingers crossed behind my back] though, as I always drove conservatively on public roads. It may be a bit more fun if we were going to cover torque as it relates to a performance engine, but I'm afraid it will be in the arena of collision repair. There is an interesting relationship between horsepower and torque as it relates to performance. It's worth diving into. After the shop closes for the day of course. As far as the aspect of torque we will discuss here goes, I do think it will enlighten your sense of the repair process as this area is typically misunderstood when it comes to bolt-on body panels and other components as well. We are all familiar with the torque specifications for a wheel on vehicles of all types. At least I hope you are and we will touch on that subject as well. I will also attempt to enlighten you on the less common areas of specific torque applications. As the vehicles we repair are changing rapidly, we should all understand the current repair procedures and adopt the changes to be a regular procedure moving forward. Some of these areas we will discuss have been in place for some time but are oftentimes overlooked by those in and outside of the shop.
I will revisit torque as it relates to what we do. Specifically with fasteners of all types. The definition of torque as it relates to physics goes about as far over my head as the clouds on any given day. I'm going to give you the definition as it relates to what we do with screws, nuts, and the like. Torque is the application of force at a radial distance while causing rotation. It is also referred to as torque loading when we are specifically discussing threaded fasteners. The word torque is derived from the Latin word twist. That background on the origin drives home the rotational aspect of torque as we know it. In simpler terms, it's the amount of pressure exerted on two or more objects where they are joined. We should all be familiar in its most common form where a lug nut or wheel screw is torqued to a specified value. The value most commonly used is newton-meter or sometimes represented as “N-M” or “Nm”. It can also be expressed in pound-foot (lb-ft). For a simple explanation of this British derived measurement, it is that one pound-foot is the torque created by one pound of force from a pivot point. Conversions can be done for either value. One-foot-pound is equal to 1.356 newton-meters. If you need to convert newton-meters to foot-pounds all you would need to do is divide your Nm value by 1.356.
Torque specifications are not to be confused with a Torque-To-Yield bolt. They are one-time-use bolts that are designed to stretch. I-CAR RTS Back-To-Basics: Torque-To-Yield Bolts (posted February 12, 2020) says this:
Sometimes going back-to-basics can make the difference between a quality repair and a failed repair. Let’s take a look at torque-to-yield bolts.
What is a torque-to-yield bolt? It is a one-time-use fastener that is designed to stretch during the torquing process (installation). Because of this stretching, the integrity of the bolt is compromised. These bolts cannot and should not be reused due to the stress caused to the bolt during its first installation.
It is important to be aware that these bolts will not have the same clamping strength if attempted to be used a second time. Torque-to-yield bolts may break if reused or become loose over time. Some common areas where these bolts are found include cab, pickup box, and suspension mounting locations. It is important to note that most repair manuals refer to these bolts simply as one-time-use fasteners instead of torque-to-yield.
The repair manual should always be referenced to ensure the correct fasteners are being used for a complete, safe, and quality repair.
Once we know what the values are, and what we are trying to achieve, a torque wrench is typically the tool that is used. Very similar to a ratchet whereas they can use different size sockets depending on the fastener. There are a few different types. Split-Beam Click Wrenches, Torque Wrenches, and Digital Torque Wrenches are some of the categories you may come across when shopping for one. Torque screwdrivers are similar in the way they function. It is at this point I should cover the variations in torque wrench sizes and types. The most commonly used and recognized size in our industry is the 1/2-inch drive version.
As stated before, the tools may be that of a 1/4-inch drive. 3/8-inch and 3/4-inch drive versions are available as well. They all arrive at the same function but may differ in the way they are used/set. Typically the value is set to a predetermined number you wish to reach. The tool will let you know in a variety of ways when that specification is reached. I'm gonna go back a few years here and tell you that some of my early ones used a needle that would climb a scale as pressure was applied. It was up to the technician to stop at the desired force. They actually use a variation of that in some tools today. It is a bit more advanced than a crudely exposed needle of days past. Popular for some time now has been the preset version where a value is entered, usually by twisting the handle at the base or “rolling” a value with a thumb wheel to the desired spec. When that specification was reached the tool would let you know. An audible click is common on regular and the split-beam versions. Digital torque wrenches may let the technician know when the preset number has been reached through a series of lights, audible tones, or both. For more in-depth education about torque wrenches take the online course offered by I-Car: Torque Wrenches
The Torque Wrench training course is designed to provide a basic understanding of torque wrenches used with collision repairs including an overview of the various types of torque wrenches that may be used. Operation and maintenance considerations for torque wrenches are also included.
We covered a bit of the basics and history to this point. I've also touched on the most common ways the torque specifications and tools are used. If you are familiar with and have been a part of wheel torque that is a good thing. Just know that is the tip of the proverbial iceberg when it comes to torque settings and specifications on a vehicle. The wheel/tire combination is important for occupant safety but the correct torque specs for bolted-on body parts, seats, suspension components, latches, and a host of other items are important as well. We have been pounding each other with the realization that today's vehicles are built and repaired differently. I'm going to borrow Jeff Peevy's line he used in a Collision Boost Radio podcast, “Its no longer your father's body shop and in fact the industry already belongs to the next generation”. This statement sums up why we must expand our existing knowledge and continue to accept change. I'll give some examples of torque specifications in areas we have typically tightened by using hand or power tools without measuring.
Below is an excerpt of a procedure for a GM truck front bumper replacement taken from an online repair information provider. This is what you may encounter when pulling up procedures for the repair and documentation that would accompany the file when completed. You should note that what would seem to be a relatively insignificant component has a specific torque specification of 58Mn (43 lb-ft). Once you understand what it is and why we need it you should be able to spot the specification when reading a procedure. They can be “off to the side”, randomly noted within or even called out on an exploded view of parts. You should now be able to quickly spot it below and have it on your “radar” moving forward.
2016 Chevy Truck Silverado 1500 4WD
V8-5.3L
Front Bumper Impact Bar Outer Reinforcement Replacement
• Vehicle
• Body and Frame
• Bumper
• Front Bumper
• Front Bumper Reinforcement
• Service and Repair
• Removal and Replacement
Call out
Component Name
1. Preliminary Procedures
2. Front Wheelhouse Liner Replacement - Right Side
3. Front Bumper Impact Bar Lower Bracket Replacement
Front Bumper Impact Bar Outer Reinforcement Bolt [4x]
Caution: Refer to Fastener Caution.
58 Nm (43 lb ft)
Front Bumper Impact Bar Outer Reinforcement
Another example is for a 2019 Honda Civic Coupe. The hood latch bolts are to be torqued to 9.3 Mn (6.9 lb-ft). These lower amounts of torque would be typically done with a smaller torque wrench such as a 1/4-inch drive version.
As I continued my searches through various manufactures I found torque specifications for a 2019 Nissan Altima front door. There were specific specifications for the hinge fasteners at the body as well as the door side. The striker had a specified torque as well. Below is a partial segment on the door striker replacement procedure:
DOOR STRIKER ADJUSTMENT
1. Loosen door striker bolts.
2. Adjust door striker so that it becomes parallel with front door lock insertion direction.
RPR-000925096-01-IIB2804J
CAUTION:
Tighten bolts to specified torque. Refer to FRONT DOOR : Exploded View.
Notice the “CAUTION” telling you that the components have a specific torque setting. You would then be prompted to click the hyperlink for the exploded view which will give the torque specifications, I noted earlier, in the parts diagram shown below. The torque values are within the wrench symbol in the picture below.
It was also interesting to note the striker bolts are a one time use only if removing or replacing the striker. More on that subject at a later time. The point to these examples is that manufacturer guidelines are to be followed at all times. I did run across “sufficiently tighten the bolts” and other similar directions. It will be common to find that there was not a specific value given by the manufacture. It may very well be that there is not a specific torque specification given for every component on a particular vehicle.
It is important to know that lubricants, refinish material, and corrosion inhibiting products on the fastener or surface it comes in contact with can affect torque outcome. Once again follow the manufacturers' guidelines when it comes to these topics. It may be that information is located in a “general guidelines” area but will give you a reason for the specific instructions you may encounter. An example might be that it would seem prudent to use a corrosion-resisting product on a bolt but the manufacture clearly states not to. The reason would likely be that they have a specific torque requirement and the addition of any substance would jeopardize that specification required.
To sum it up it is important to be vigilant about the various areas torque specifications are used and to be knowledgeable about the tools that allow that procedure to be completed. The examples I used are that of vehicles that are several years old. That was done on purpose to show this is not a new area of concern. I know this was along read but anything worth knowing or doing typically takes time. The upside is you've earned that “track time”! Now that you've studied torque in the shop, and know there is a difference, you've earned the right to “study” it at the track!!
