torque wrench calibration

[Fleetwood]

Finishing front suspension refresh and I'm questioning the calibration of my 35-40 year old budget torque wrench. Wrench worked as expected on 17 ft lb hub bolts and 47 ft lb control arm bolts and seems to be performing perfectly but since this is my largest repair to date I'm questioning all my processes

This wrench has been used pretty much exclusively on lug nuts with the setting at 94 ft lbs most of the time. Recent reading indicates I should have reset the wrench to near zero while resting but that rarely happened.

Searching this forum even with the special search engine left me even more undecided. My wrench looks just like the $24 Harbor Freight model that received good reviews here...should I just buy another and compare the two or take another path?

Thanks ahead for the council

[walt]

Clamp the square drive of the wrench in a vise and hang a known weight a known distance from the sq. dr., alternately you can use some type of pull scale instead of the weight. This should get you very close. I do always make a point of returning the torque setting to zero.

[aus911]

Hi Fleetwood,
I had a bad experience with my torque wrench a few years back, and broke an ear off my 3.2 manifold....grrrr
I ended up generating a basic spreadsheet that converts Nm/fLb to kg per cm.
You insert the required torque and the length of your torque meter and it lets you know the expected kg. It makes it quick and easy to check your torque meter.
It is worth the effort if you are unsure.

[john walker's workshop]

Most tool trucks have a tester on board.

[HarryD]

I periodically compare my clicker to my beam style one to see if they agree.

[1QuickS]

Clamp the square drive of the wrench in a vise and hang a known weight a known distance from the center of the square drive, alternately you can use some type of pull scale instead of the weight. This should get you very close. I do always make a point of returning the torque setting to zero.

Do the above, you can check your calibration weight at UPS or FedEx on their digital scale.

Torque is product of weight (lbs) x distance (inches or feet) from weight to middle of square drive. Hang a weight on a wire from the torque wrench handle. My torque wrench (ancient Craftsman) has a set screw that allows adjusting the indicating ring to agree with actual torque output. I hang my calibration weight from a wire at a distance from the square drive and calculate the torque. I then adjust the clicker handle, one ft-lb at a time until wrench clicks. I then set the indicating ring to agree with the torque. For critical torque applications I suggest calibrating your torque wrench at the torque you seek.

[David Inc.]

You can also buy a digital torque drive for $40-$50 that will be very accurate. I use mine all the time and used it to "pretty close" calibrate my clicker wrenches.

You'll notice when doing so that the clicker wrench will let the torque creep as you apply and re-apply, and how quickly you approach the release in the wrench will also effect peak torque. On my lug nuts my clicker wrench might go from 95 - 105 depending on how I used it.

[Dr J]

I have a high quality and a low quality torque wrench. The hi quality I suspected was tightening too much and the low quality too little. You can indeed calibrate and adjust the wrenches. I looked through a few youtube videos and was able to fix both of them. Torque = force x distance so you hang a known weight a measured distance from the center of where the socket goes. Ex. 20 lbs 1 ft distance is 20 ft-lbs. The same 20 lbs 2 ft away is 40 ft lbs. I had a hand-held digital scale for weighing luggage and used that. If you calibrate at one value try to use the torque that you need the most often. It is important that you pull perpendicular to the wrench.

This is kind of how I did it. Though this video does not tell you how to adjust the wrench.

https://youtu.be/XaqBA-xSGbc

This one does.

https://youtu.be/fybLYL0WfFY

Other torque wrenches you have to remove the bottom cover and adjust the spring tensioner. Keep looking on YT until you find someone doing a wrench like yours.

[HarryD]

FWIW. I discussed torque wrench calibration with the fellow at work who does them for military aircraft. He told me:

1-To use, set to desired force. Against a fixed object, click 3-4 times then use. This sets the spring to the correct tension.

2-To store, release tension to the lowest setting not zero. This allows the spring to relax but not lose its repeatability.

3-I had him check my Harbor Freight wrenches. All are with spec. He told me he has tested many of them. Never had a failure.

[Synchro Joe]

If you're serious about the accuracy, there is likely a 'local" Torque Wrench Calibration Service and Testing shop/lab in your area. Or if you can look around for the various tool vendors that service the auto dealerships in your area, etc. In another lifetime, we used to do mechanical calibrations in our military precision measurement labs supporting agencies like NASA, FCC, etc. What Harry D says above seems to be correct in general terms, but my experience was many, many years ago.

[Fleetwood]

Thanks for all the input. Military background is causing me to overthink this. First local calibration place wanted $58 so I'll check others, maybe even O'Reilly's does it? Youtube is next. I'm liking the vice idea but no vice at the winter residence so I may go on the search. Thanks for all the options

Have noticed a little torque creep if I retorque bolts and speed to the release point may impact final measurement

[Steve W]

You might not have a vice, but you probably have a car. This is how you can calibrate your torque wrench:



Put your wrench against a fixed nut (in this case it's a hub nut), and hang a known fixed weight a measured distance away from the socket. In this case it's a 35 lb weight 12 inches away from the socket. Torque = force * distance. In this case the weight is 35 pounds and the distance is 12 inches (1.0 ft), so the torque produced is 35 * 1 = 35 ft/lbs.



Use a jackstand to support the socket extension near the end where the wrench is as pictured.

With the same weight above, if can test for 70 ft/lbs by putting a cheater bar (such as your jack handle) on the wrench and hang the 35 lb weight 24 inches (2.0) ft away from the socket 35 lbs * 2 = 70 ft/lbs.

Say you want to test a big torque wrench to confirm calibration at 250 ft/lbs because you need to torque a big axle or crank nut. You could use your body weight and stand on the handle a fixed distance from the nut to produce the torque. For example if you weight 170 lbs, distance = torque/force. So 250/170 = 1.47 ft, or about 18".

1/4" inch/lb wrenches can be measured and calibrated the same way. A 5.0 lb weight hanging 10" away from the socket is 50 in/lbs.

The torque wrench you have pictured in your post looks like the Harbor Freight type and you can easily calibrate those to your measurements. The big black hex nut at the bottom of the handle unscrews separately from the chrome handle, after which you can reset the handle indicator marks to match your measurements.

On the higher quality wrenches, such as the one pictured above, there is a cap you pop off the end, that allows you to access the nut settings to calibrate the handle to the readings.

[shoooo32]

These pop up used on eBay from time to time. We don't have a tool truck stopping by, so it was easier just to mount one at the shop.

Also of note, I've been buying those cheap Tekton 1/2 torque wrenches for $37 off Amazon to torque wheels. I beat the first one like a rented mule; drops, loosened lugs with it, never returned it to zero, and it's still holds 90 ft/lbs +/-3. I now leave one in the trunk of each car. Works way better than a stock lug wrench in an emergency and they're surprisingly accurate.

[yelcab1]

I calibrated all my wrences once a year to an electronic meter. You gotta trust something.

[Superman]

Before rebuilding my engine I took my Harbor Freight torque wrenches to the guy at the airport that calibrates them. They were perfect. Some guys will assemble an engine with a breaker bar. Honestly, I use a torque wrench for lug nuts, flywheel and pressure plate bolts and perhaps a few other things, but really the key is to get it on tight enough and to have all the fasteners oriented in a circle be at the same tightness. That's all. But again, I do get persnickety when it comes to flywheel bolts especially, and also PP bolts and lug nuts.

[Fleetwood]

Dr J recommended Youtube and Steve W helped me solve this question. Wrench setting was 40 ft lbs with actual reading in the 32-35 range per the Youtube calibration video. Adjusted spring tension and consistent readings at 40 lbs on the $6 luggage scale.

Compliments to all who post detailed replies to novice questions. Makes my 35 year journey with this 911 so rewarding