Two of the 20 on the car snapped before reaching 87 lb ft (117 NM). I know the torque spec now (76 lb ft.) but all the remaining 18 nuts were torqued to 87 lb ft and I had no issues.

The service manager at the local dealership indicates the yield point of a wheel stud is not available.

I want to know what the actual yield point is incase I've stretched the remaining studs to the point that I should consider replacing all of them just to be safe. I know that's overkill but I find it impossible that this information is not available.

Before you ask, yes the torque wrench is not perfect but it's been certified not too long ago and is stored properly.

2014 ES350

Thanks for your help

 

As you may know there are some variables related to torquing lug nuts or any bolt for that matter. One of the main issues is the amount of lubrication (or lack of) on the threads. Lubes can greatly change (increase) the load on the studs with the same torque setting. Possibly the broken studs had some unseen lube? Lug nuts and studs are supposed to be "clean and dry". I expect these variations are the reason I have never seen a fastener yield strength expressed in terms of torque. Also that is why torque-to-yield head bolts have a rotation spec not a torque spec.

Since exceeding the yield strength causes permanent elongation you could conduct a test on your wheel studs by removing the wheels and then hand thread the lug nuts onto the studs. If the threads on the stud are stretched significantly, the nut will bind up where the stud thread pitch no longer matches the nut thread pitch indicating that stud has been stretched.

 

I am surprised that over-tightening the lug nut by just 11 lb ft would cause the lug bolts to break. I have had cars come back from wheel/tire shops over-tightened by much more than that - thanks to impact wrenches. And that is why I always check them as soon as I pick up the car.

Dave Mac

 

Same here. Sometimes I need to use a breaker bar to loosen them and then I retorque them back. It's a bear change a flat out in the middle of nowhere with lugs jammed in with an impact wrench at the last service.

 

Good point!

 

Thanks for the comments and reminder about lubrication. You have a good point there that I didn't think of.

I often smear just enough anti seize to coat the two mating surfaces and then wipe the excess off with a rag so it is possible that I partially caused my own issue.

Either way, it isn't the end of the world. I simply paid (~$290) them to replace all 5 of the studs on that corner as I suspect someone at that dealership over tightened them when they serviced the brakes (apparantly Lexus/Toyota stopped applying lubrication to the brake pads leading to some popping noise when releasing the brakes).


Merry Christmas Everyone