Bolt stretch

[Sprintcar26]

Having the usual "brake job' tire repair/replacement, anything that requires the wheels coming off" problems with over-zealous "mechanics" with impact guns. Try to retorque lugs when I get home, but I live in NYC and it's kind of cold for driveway work, and sometimes you can't even get the lugs off without a major effort. Last visit I have a long conversation with the owner- "lugs nuts to 76 lbs", but made the mistake of telling him that I retorque them myself. He says "ok so just retorque them after we put them on". Pick up the car and ask the mechanic about the 76 pounds (note on the dash, notwithstanding) he says: "oh they're good and tight-I'll make them tighter if you want." I say no, they're supposed to be 76 pounds, and he points to the air valve and says : "76 pounds in the tire?" So my question is: does it matter "bolt stretch wise" if you pull them apart right after you get home, or leave them be for two months or so, and then redo them? Does the bolt stretch take a set so that it becomes "too late to rectify"?

 

[ctechbob]

If they're beating them on hard enough to stretch the bolt it will be permanent and instant.

 

[Exhaustgases]

I see no reason to even have to deal with a shop for anything like that. When I need tires the bare wheels go to have them mounted.
No one ever tightens any bolts on my vehicles. Period. Maybe if the wifes car needs an alignment then? I do my own.

 

[cci]

Having the usual "brake job' tire repair/replacement, anything that requires the wheels coming off" problems with over-zealous "mechanics" with impact guns. Try to retorque lugs when I get home, but I live in NYC and it's kind of cold for driveway work, and sometimes you can't even get the lugs off without a major effort. Last visit I have a long conversation with the owner- "lugs nuts to 76 lbs", but made the mistake of telling him that I retorque them myself. He says "ok so just retorque them after we put them on". Pick up the car and ask the mechanic about the 76 pounds (note on the dash, notwithstanding) he says: "oh they're good and tight-I'll make them tighter if you want." I say no, they're supposed to be 76 pounds, and he points to the air valve and says : "76 pounds in the tire?" So my question is: does it matter "bolt stretch wise" if you pull them apart right after you get home, or leave them be for two months or so, and then redo them? Does the bolt stretch take a set so that it becomes "too late to rectify"?

I'm pretty sure there are folks here who can give a better technical explanation, but ctechbob (above) is taking you in the right direction.

Yes, torque, clamping force, bolt stretch, all very important considerations, but what we're really concerned with here is whether the steel is behaving in an elastic or inelastic manner. For example, when I am building an engine, the head bolt and insert threads all get cleaned carefully, I am using a specialty lubricant on the head bolt threads, and I am torquing the head bolts (also specialty fasteners) to a particular spec because this is stretching the bolt in a desirable manner -- it's not just that we are producing a specific calculated clamping force, it's also that we want the bolt to stretch a desired and specified amount that is inside the elastic limit.

Where we run into problems with too much torque is when the fastener behaves in an inelastic manner i.e. cannot go back to it's original dimension when the strain is relieved. We don't usually think about bolts stretching in a desirable manner, but that is the reality.

ctechbob is correct, if the bolt (in this case, lug) was taken past its elastic limit you'd already know it. Just back them off, torque to spec, and if nothing is broken and no threads are deformed it's unlikely that there's any residual damage or problem.

For example, the spec for the lug nuts on my Freightliner was 400 foot pounds, I got it back from a shop and checked their work, 3/4" breaker bar with about 180 pounds on the end of a 5' of cheater pipe wouldn't break them. Do the math. Yep -- more than double.

Once I got them loose and re-torqued them they were fine.

 

[IndyIan]

Just loosen one by one and retorque at home, then you know. Also depending on how clean and corrosion free everything is(which you don't know, since the wheel isn't coming off, I would just put them at 85-90 ft-lbs, and they will stay tight. I've used a low torque like that and had the lugs come loose on a wheel that had bit of rust on the important surfaces.

 

[boom10ful]

I see no reason to even have to deal with a shop for anything like that. When I need tires the bare wheels go to have them mounted.
No one ever tightens any bolts on my vehicles. Period. Maybe if the wifes car needs an alignment then? I do my own.

I agree as well. I've had them cross thread and overtighten my lug nuts that it's not worth them "installing" them on my vehicles.

 

[D60]

I figure 80% of the vehicles on the road are running around with lugs either too tight or too loose. If nothing is snapping or falling apart, I wouldn't sweat it.

I absolutely DO torque all wheels, but most tire shops, service centers and DIY suburban driveway dads do not.

I was always taught the greatest risk is theoretically warping a rotor or inducing brake vibes from overly tight lugs.

If it's M12 (typically the smallest you'll find on most passenger cars) I usually won't go less than 80ft lbs no matter what the manufacturer says.

On an '02 Impreza, Subaru says 67. But on a later Outback with the same lug studs, lug nuts and number of lugs, they call out more (it's possible the bolt circle changed by 4.3mm ‐‐ big deal). Thus I can only conclude they're adjusting torque by vehicle weight -- a practice with which I simply don't agree if the fasteners themselves and wheel material are identical (they are).

At the very least this tells you the fastener can withstand more torque than the lower number spec'd

I also don't like Toyota's 76 ft lbs on alloy wheels with their counterbored holes. Even on a heavier car like a Camry it makes me nervous, and I definitely wouldn't do it on a truck like a Taco. That said, these are seating on a free-spinning flat washer rather than a conical seat, so the dynamics of everything are different. I still go 85-90 and have never seen a problem from doing so (FWIW something like a '17 Taco is technically 83 ft lbs)

The problem comes when people lay into them with an impact for SECONDS even after they've snugged up. You can easily hit 170+ with my daily use mid torque Milwaukee

I feel like many vehicles are moving to M14 studs as they get heavier, which I think is great. The JL is M14 while the previous JK was 1/2" IIRC. I personally torque all M14 studs to 140, period. My JL says 130 -- I don't care, I'm running 37" rubber

 

[Exhaustgases]

I agree as well. I've had them cross thread and overtighten my lug nuts that it's not worth them "installing" them on my vehicles.

And this is also how to have a truck or car that lasts a long time. Don't let anyone with a tool near it.

 

[Sprintcar26]

Thanks to all for the responses.

 

[The_Jeff]

I also don't like toyota's 76 ft lbs, have had two of their washer-style alloy lug sets come loose on me. And that's using a torque wrench that I later verified was in spec when I had the opportunity to test it.

I go to 100. Why? Because a M12x1.5 stud can "take it" on GM and many other makes.

That doesn't cut down OP's desire for their mechanic to do things by the book. It's a good starting point and arguably correct. Their sandbagging answers (76 PSI? Huh?) would make me not want to return.

To answer your question, ctechbob is correct. Lugs that run down roughly indicate stretched studs if no corrosion is visible.

 

[Donald]

And then there is a "when was your torque wrench last calibrated" question . Was the torque wrench (if a clicker) run down to the minimum torque on the handle when you put it back in the case. Or is it just tossed back in the pickup bed in a tool bucket?

 

[f355spider]

And then there is a "when was your torque wrench last calibrated" question . Was the torque wrench (if a clicker) run down to the minimum torque on the handle when you put it back in the case. Or is it just tossed back in the pickup bed in a tool bucket?

I learned from the Costco HQ automotive buyer that every Costco tire center owns a torque wrench bench tester. Every torque wrench they own is tested each month, and the test is logged in their records. They also have a software program with every car and truck listed with the appropriate torque specification. For trailers and things not in their data base, they require you to provide the owners manual with the specification.

I have actually sent my torque wrenches (Utica Tools) back to the factory for testing/calibration. They were both fine and I received a certificate for each, showing the tolerance in each direction.

 

[f355spider]

I got in the habit of loosening and properly torquing lug bolts after getting a flat tire 35 years ago. Had a flat tire and changed it on the side of Interstate 90 out in the desert of Eastern WA. Bolts were installed by someone who thought that impact wrench was a machine gun...probably 125 lb/ft. I have the little cheesy wrench cars come with and I am literally standing and jumping on the thing praying the wrench doesn't snap or bend. I eventually got them all loose...but never again.

I have very few trusted service providers where I don't immediately loosen and retorque my lug bolts when I get my cars or truck home. Even when I explicitly ask them to "use a torque wrench". The Ferrari dealer is the only place where I have seen them using a torque wrench during service. They would also recheck after the test drive with the torque wrench again and both checks are actually documented on the invoice. I'm sure they do that for liability. Not sure why all service departments wouldn't, that liability is immense.

 

[Donald]

Does anyone carry an cordless impact in their vehicle tool bag? In reality if it's in your vehicle then you don't need an extra one, you just store your cordless impact in your vehicle rather than rolling toolbox. Recharge the battery a couple of times a year.

 

[AdmiralYoda]

My father had an auto repair shop for 40 years and started his mechanic life with his father who had a shop for 25 years before that. Wheels get installed tight with a 1/2" drive air impact wrench....tight. In general the only professional mechanics that torque lug nuts are those in premium dealerships, like Porche, MB, BMW, etc.

I'd be willing to bet the majority of the time the lugs are over torqued by your regular mechanic. 99.99% of the time that won't matter one bit.

In your typical independant shop if somebody comes in and tells the the shop specifically how they want a job done or to follow some listed procedure or just a verbal to "torque the lugs to XX lbs", they are going to labeled as one of "those" customers.

Falls into one of these:

• Labor is $150/hr
• If you want to tell me how to do it it is $175/hr
• If you want to watch it is $200/hr
• If you want to help and show me how you want it done it is $250/hr.

If you really insist on them torquing the lug nuts, whoever is doing the service is going to have to borrow the torque wrench from the one mechanic that actually has one. Then you will rely on a tool that wasn't calibrated since it was new in 1997.

Just let them do their 5 ugga-duggas and everything will be fine.

 

[The_Jeff]

In your typical independant shop if somebody comes in and tells the the shop specifically how they want a job done or to follow some listed procedure or just a verbal to "torque the lugs to XX lbs", they are going to labeled as one of "those" customers.

The top three complaints of car repair shops are that they're too expensive, take too long, and over torque lug nuts. They can't control the first two but the last one is an easy win from a customer service perspective.

I briefly worked at a tire shop and actually torqued things right-- we had multi-colored clicker wrenches in increments like 80, 100, 125 ft lbs. So yeah Toyotas for 76 got 80, a negligible difference. The nuts rotated when I worked, but rarely did for anyone else. For them the clicks were confirmation that things were "tight enough if not tighter." Their understanding was basically they didn't want the wheel falling off, for which they got in trouble.

We were supposed to 2nd check each others dipstick levels and tq wrench clicks, but only really did so if there was enough help to spare.

 

[Chris142]

Lose that jack shop. I run them down with a 65 ft lb torque stick then finish with a torque wrench.

 

[John Galt]

I have had four sets of tires installed on four different cars at my local Costco over the last 5 years. I stick around and watch. My Costco uses a torque wrench on all the lug nuts for the initial install and they instruct the owner to come back in a week to have them re-torqued to spec with a torque wrench. They also use a torque wrench when they do the included tire rotations. They do this on all the cars not just mine because I’m watching. The proper torque setting is written on the work order.

This is one of the reasons I use Costco for tires, my local name brand tire shop just used an air impact gun. Not a fan of air guns for installation, ok for removing lug nuts.

I did see manual electronic readout torque wrenches used on tire installs at the Audi dealer on my A6 after a rotation. Not sure what the Ford dealer does since I can’t see the technician but that shop is spotless, on the level of the Audi and Mercedes service areas, so I expect they also do it right.

 

[Sprintcar26]

Thank you all. I try to restrain myself, but I guess I'm one of those customers they would want to charge $250 per hour!

 

[rcube]

My father had an auto repair shop for 40 years and started his mechanic life with his father who had a shop for 25 years before that. Wheels get installed tight with a 1/2" drive air impact wrench....tight. In general the only professional mechanics that torque lug nuts are those in premium dealerships, like Porche, MB, BMW, etc.

I'd be willing to bet the majority of the time the lugs are over torqued by your regular mechanic. 99.99% of the time that won't matter one bit.

In your typical independant shop if somebody comes in and tells the the shop specifically how they want a job done or to follow some listed procedure or just a verbal to "torque the lugs to XX lbs", they are going to labeled as one of "those" customers.

Falls into one of these:

• Labor is $150/hr
• If you want to tell me how to do it it is $175/hr
• If you want to watch it is $200/hr
• If you want to help and show me how you want it done it is $250/hr.

If you really insist on them torquing the lug nuts, whoever is doing the service is going to have to borrow the torque wrench from the one mechanic that actually has one. Then you will rely on a tool that wasn't calibrated since it was new in 1997.

Just let them do their 5 ugga-duggas and everything will be fine.

I've had to replace lug studs with stripped threads on several cars that had only been to a shop to have new tires installed. I have also replaced numerous lug nuts with rounded corners. I do all other maintenance on those cars myself, and use a torque wrench. My daughter also bought a used car that had the oil pan drain bolt threads stripped, and I would strongly suspect someone used an impact wrench on that bolt.