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The mkiv Supra Owners Club

Another lucky escape


JamieP

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I'm struggling on the bit I've bold/italic'd above, but are you saying that if they're not torqued-up tight enough, then a bang/kerb mounting like what happened could cause them to fail in the way they did?

 

I doubt it was the kerbing that caused the damage and as JamieP later explained the studs were already fractured with rust across the fracture zone. This shows the problem has been lurking for while. A disaster waiting to happen. The bump was the last straw.

 

Torque setting is MEGA important and not just for wheel nuts. I would say these were overtightened past their elastic limit into plastic range then past the yield point. Repeat everytime you change your wheels. Cracks then developed across the studs. The stud tensile loading then drops off considerably. Relative movement occurs between hub and wheel. JamieP swears blind it's nothing to do with torque setting but the studs do not transmit the wheel torque. That would mean 5 studs would be subjected to a combined shear and tensile loading. A splined shaft does this better. The studs hold the wheel to the hub with sufficient frictional load that there's no relative movement. It is the contact surface swhich transmits the engine torque to the wheels.

 

Every bolt/stud joint has a minimum torque level as well as a maximum. This is required to preload the bolt into its elastic limit. Simplistically the bolt behaves like a super high load spring. If undertightened there will be no preload and the joint can shake itself apart. For some applications spring washers are use to add preload.

 

Jumping on a wheel brace to FT setting isn't good enough. Get a calibrated torque wrench.

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So.. ive taken wheels on and of my cars 100's of times and never had a problem with the studs, first time i wack a curb they all snap within 50/60miles.. thats some coincidence.

As for the rust on half way throught the studs.. that would happen first time i washed it... this morning in fact.:)

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Elastic, plastic, Fantastic!

 

Maybe studs should be treated as a service item perhaps?

 

Also, any recommendations for a torque wrench? i really should invest in one.

 

The ones we use on our assembly, test and development are Snap-On. They cost a fortune! But the important bit is they get calibrated every month.

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But the question is, can you nick me one? :p

 

Strange you should say because last week our Yank owners announced they're closing down our UK site and transferring all engineering, design, development, A&T to Germany. I'm sure there'll be sheds loads of stuff to be rid of. I'll get you a two man torque wrench to stick in your boot. It's about the 2 m long and weighs about 50 kgs. We use it for tightening 200 mm a/f nuts.:blink: No chance of undertightening yer nuts!

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