Torque Wrench How To
How I fixed my Click Wrench
Recently I found out the hard way that my click-style torque wrench no longer "clicks". While rotating my tires, I sheared off a wheel stud by over torqueing it (the shop I last visited had also way over-torqued the nuts, weakening them). Upon playing with the wrench some more, I discovered that it no longer operated properly. Since I got it rather cheaply at an auto parts store, I didn't feel like shipping it off to be repaired or for me to be told it was broken and needed replacing. Being a bit handy dismantling things myself, I decided to take it apart to at least see the internals and find out how it works, and attempt a repair. As it turned out, the fix was even more simple than I expected, and my wrench is now fully functional again. As I was unable to find any info out on the web about these things, more than just board postings of hints and a couple how-to-calibrate pages, I decided to post this page for the benefit of all. The following is a description of what I did, along with pictures and my analysis of how it works.
Please note: I am not responsible for anything you do. This page is just a description of something I did to a wrench I own and use. This should not be looked upon as an official way to do anything, and by reading any further, you acknowledge that you will not hold me liable for any damage to your tools/equipment/stuff/self/etc as a result of this page. Read it as a reference, use it at your own risk!
Pic 1, the wrench, fully assembled, not clicking.
This as you can see, is a Torque Wrench. This particular one is a simple twist the handle to set the torque one, with the torque settings engraved in the handle, read like a micrometer. To keep from accidentally adjusting the torque while you are torqueing something, there is a knob on the end that you screw into the handle to lock it in place. The ratchet is reversible like a normal ratcheting wrench is, via the switch, but the click is only functional in the tightening direction (unless the head itself is reversed, see later in this page).
The way this wrench is supposed to work is this: you dial in the torque by twisting the handle until the reading engraved on the handle matches your requirements, you then place the socket on the head and tighten the bolt/nut until the wrench makes an audible "click". Some fancier wrenches have windows with a readout to actually display the torque. These wrenches are probably similar in how they work, but disassembly is probably at least a little different. As this is a precision measuring device, it should only be used to measure and adjust the torque of fasteners, it should not be used as a drive ratchet. What I mean by that is you should pre-tighten the nut/bolt at least finger tight using another ratchet or tool so you are only using the torque wrench to adjust that tightness to your required torque.
Pic 2,3 First step to dissasembly.
This shows the first step to taking apart my wrench. Please note that when I did this, there was some trial and error, but to keep this page to the point, I'm skipping all of that. The starting point was the wrench with the lock-knob unlocked, and the handle unscrewed until there was no pressure on the spring (a noticeable reduction in force required to turn the handle). To be sure, I just unscrewed it as far as it would go.
Step 1 was to remove the calibration lock nut that is at the end of the handle. This is the large nut that threads onto the calibration sleeve, which threads into the handle. This nut uses its tightness against the handle and the threads of the calibration sleeve to keep the sleeve itself from turning, and thus throwing the wrench out of calibration.
Pic4 Release the handle from the spring.
Step 2 was to remove the calibration sleeve from the handle. The sleeve is a fine threaded metal cylindar with one closed end that interfaces with the piston to put pressure on the spring. By threading more/less of it into the handle, the wrench can be calibrated so that the measurement engraved on the handle actually match what makes it click. It also has holes in it for pins that work with the lockout knob assembly to keep it from turning when in use. To remove it from the handle, it was unscrewed while twisting the handle to a higher torque setting, but keeping all pressure off the spring. The handle was twisted only to allow the sleeve to come free of the handle, twisting too much would put pressure on the spring and make it hard/dangerous to remove
Pic5 Removing the adjustment assembly
Step 3 was removing the lockout knob and whole adjustment assembly from the wrench body. As you can see, the lockout knob, calibration sleeve and piston are designed to move up and down along the track cut in the wrench body. There is a pin that holds the piston in the track, keeping it from twisting and from being pulled out. The handle itself keeps the pin in place under normal operation. To remove the assembly, the handle has to be removed. The piston has a screw in it that keeps the lockout knob from unscrewing all the way out. This is also to keep the pins that are in the calibration sleeve from falling out. Once the retainer screw is removed, the lockout knob can be fully unscrewed from the piston. This allows the knob, calibration sleeve and piston to be separated from each other. Once the calibration sleeve is removed, the handle can be unscrewed until it comes off the wrench body. Once the handle is gone, the pin holding the piston in place is easily removed. Once that is removed, the piston easily slides out of the wrench body.
As to how the lockout knob works, here is a description. As you can see in the pics, as the knob is tightened, it increases pressure on a washer. This washer pushes 4 pins through holes in the calibration sleeve to interact with pits machined into the piston. When tightened, the pins dig into the pits, locking the calibration sleeve in place, and if the calibration lock nut is in place, locking the handle in place as well. This comes in handy when calibrating the wrench, as you have to lock the lockout knob to put the lock nut back in place without having the nut turning the calibration sleeve (and thereby loosing the calibration just set).
Pic6 Removing the spring and clicker, and how it works
Step 4 was removing the rest of the mechanics of this end of the wrench. The spring and clicker mechanism slid out when I angled that end of the wrench down. The spring and the clicker are the main components that make this wrench work (or not work, as was my problem). If you look at the picture looking into the wrench body, you will see the end of the arm that is an extension of the ratchet head. The ratchet head itself is attached to the wrench body with a pivot where the wrench body meets the head. All the torque generated with this wrench to tighten/loosen a nut/bolt is transmitted along that arm, and is transmitted into the body through the pivot point and the click mechanism. The spring puts force on the clicker, keeping its roller bearing pushed into the groove on the end of the arm. This keeps the end of the arm against one side of the wrench body. When the torque is strong enough, the arm pushes the clicker back against the spring, the roller bearing rolls out of the groove, and the arm is allowed to quickly move to the other side of the body, under the force generated from the torque. This quick movement ends when the arm hits the other side of the body, generating the "click" sound. When torque is released, the sloped shape of the end of the arm combined with the pressure from the spring force the clicker back down, pushing the arm back to the original side of the body. This results in another "click" as the clicker's roller bearing is pushed back into the groove and the arm is pushed into that side of the body. The roller bearing is used to reduce friction on this movement, as friction would cause a variable force to be involved, greatly reducing the accuracy of the wrench. You may have noticed that the clicker itself also has 2 ball bearings on one side. These also reduce friction, but these reduce it from the interaction with the wrench body. The clicker moves up and down along the body as the arm moves under torque, and since the arm has a sloped end, it is always in contact with only one side of the body, hence bearings on only one side. Again, this is simply to increase the accuracy of the wrench. While it is out, it would be a good idea to add a little more grease to the bearings to aid in friction reduction. The roller bearing axel is a pin that easily comes out, revealing the inside of the clicker as just a hollow cylinder with one closed end that contacts the spring. When re-assembling, be sure the clicker is dropped in with the ball bearing side away from the sloped face of the arm, and the roller bearing is aligned with the groove in the arm to ensure the bearings will do what they are supposed to do. This is where my problem was. The clicker had turned sideways and was lodged in such a way that the arm was stuck and would not click to the side. How it happened was probably my loosening the handle too far when storing it, backing the spring off of the clicker, and giving it enough room to turn so the bearing went across the groove rather than lay in it. Once re-assembled correctly, it worked fine.
Pic8 Exploded view
This shows a view of the handle end of the wrench completely taken apart, with the parts lined up relative to how they fit back together (ie: exploded view).
Pic9 Ratchet Head
The ratchet head was easily disassembled, as there were only 2 Phillips screws holding the cover plate in place. Once removed, the two ratchet arms and their springs were easily pulled out, as was the large rotating drive head. To make the wrench measure torque in reverse (useful for left-hand threaded things) I can simply take out the drive head, flip it over so the socket adapter is on the same side as the directional switch, then put the head back together. As seen from the pic, the ratchet head works the same as any normal ratchet. There are 2 arms that are spring loaded, with pivots on one end. The other end catches the teeth on the drive head. The directional switch holds one of the arms away from the drive head while allowing the other to contact it. When the head turns one way, the arms can move against the spring allowing the teeth of the drive head to slip past. When the head rotates the opposite way, the arm catches the tooth and prevents the head from turning any further.