Torque Limiters: how do they work?

[Mike]

I hate it when shops install rims using an air gun. Once I get the car home, I’ll loosen the lugs and retorque by hand.

The mechanic at the shop I go to most often let me inspect the torque limiters he uses when installing wheels. From what I could see, they were just color-coded solid metal extensions with a socket head. There was no obvious “break away” mechanism, and he couldn’t seem to explain precisely how they were supposed to work. Are torque limiters a myth perpetuated by the industry?

Topic

[Jon Hart]

A torque stick is designed so the lug nuts are not overtightened when using an impact to install them they work like a torsion bar absorbing the impacts when they reach there predesignated torque spec. here not as accurate as a torque wrench but better than just using an impact alone. Most Torque sticks come with a warning on them saying that they are not a replacement for a torque wrench in my experience they are never more than a few Nm off. but that might change as mine get older.

[zero]

[quote=”Fmxvxx” post=137516]not a replacement for a torque wrench in my experience they are never more than a few Nm off.[/quote]

You need to calibrate toque “sticks” to both the gun and the shop’s air supply. An 80ftlb stick on an IR 2135 won’t apply the same torque as on a $100 impact. But most guys just hammer until they stop turning. In the end, there is NO replacement for using a calibrated torque wrench set properly.

I have personally played around with the setting on my gun so I have it set to the lowest setting, which is about 75ftlbs and just hand torque on the last 5ftlbs. That being said a few feet of overtorque shouldn’t do any real damage. Personally if a stud that’s supposed to be torqued to 80 breaks when overtorqued to 100 breaks. It needed to be replaced anyway. Unless you’re talking about putting them on to the point that only the hands of good can loosen them, that’s obviously different.

[Mike]

Thanks for the info.

Seems like they’d be really easy to misuse, to the point where they aren’t doing the job they were intended to.

[Josh G]

Agreed they will never be as accurate as a torque wrench, but I think they are close enough. I know it’s best to have a lug torqued to spec, but there is probably a pretty wide range of torque that won’t have any negative effect on a lug. As with any trade there’s the “technically right” way to do something and there’s the way it’s done in the real world.
For a shade tree mechanic it makes sense to torque a lug nut because you have the time to do it, but a tire shop that sees hundreds of vehicles it’s just not realistic to expect them to hand torque lugs.

[James O’Hara]

Fmxvxx explained how it works just fine as for how accurate they are it all depends. Shop air, torque of the impact, age, abuse, etc. I believe the most accurate ones are +/- 10% of the torque value new. Things start getting really iffy really fast when you are using 450ft lb ones. I only ever used one torque value lower then the supposed one and torqued afterwards and never had an issue. For a while honda had some real issues with people bending rotors due to impacts.

If I ever were to buy them I would buy the extensions. They are normally cheaper and you can use any socket that fits on them so why not.

[Author]

Replies