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Just now I was installing new lock nuts on the front left LCA, lower shock mount clip/bracket and while I was tightening the outer of the two, the bolt that goes through the ball joint and eccentric snapped at around 95Nm.
I checked both my WSM and pocket spec book and both indicate 120Nm. Double checked the torque wrench.
I then proceeded to duplicate my idiocy on the right side, same outer bolt. Snaparoo. This one let go around 102Nm.
What the heck am I missing? Torque wrench batteries are fresh according to the meter. Am I reading the manual wrong, or is the manual wrong? Is this what they meant by "Use the Force"? Im baffled and embarrassed. No more car tonight. Beer
The torque spec is right. If the studs weren't corroded, I'd check the torque wrench or, perhaps, unit scale selection.
^^^^^^^^
Agreed. Bolts could have been culprit.
When was the last time you had the torque wrench checked.
Personally I have mine checked twice a year. But I use them a lot.
The nut in your hand dose not look the same as the nut on the ball joints?
I put balljoints on my 80 this year. The original studs held Torque spec fine.
The torque spec is right. If the studs weren't corroded, I'd check the torque wrench or, perhaps, unit scale selection.
Double checked and unit scale was correct. Studs with brackets were just re-cad-plated. No measurable corrosion prior to plating.
Originally Posted by Mikebte
^^^^^^^^
Agreed. Bolts could have been culprit.
When was the last time you had the torque wrench checked.
Personally I have mine checked twice a year. But I use them a lot.
The nut in your hand dose not look the same as the nut on the ball joints?
I put balljoints on my 80 this year. The original studs held Torque spec fine.
Flanged nuts on the ball joints were put on last week, supposedly the flanged nut is what the original supersedes to, but seemed strange. So I got a set of original style (like the one in my hand) and I was swapping them on.
Same nut also went on the rear front eccentrics and torqued down just fine on both sides with the same wrench, but I'll have the wrench checked anyway, that's a good idea.
You state the support bracket was replated together with the studs. Personally I would not have had the studs treated like this given they are high tensile material. I seem ot remember that elecro-plating can cause hydrogen embrittlement of high strength steels
I am left wondering if the plating process has thus weakened the strength of the studs- just floating this for discussion purposes.
You state the support bracket was replated together with the studs. Personally I would not have had the studs treated like this given they are high tensile material. I seem ot remember that elecro-plating can cause hydrogen embrittlement of high strength steels
I am left wondering if the plating process has thus weakened the strength of the studs- just floating this for discussion purposes.
I'm wondering too, I have an entire car full of replated hardware.
Originally Posted by GlenL
As both sides broke, this sounds like a lead.
Are those flange nuts also self-locking? Where'd you get them?
Also, you're reminding me to get my torque wrenches calibrated. Or get new, nicer ones.
Yeah the flange nuts are locking, got them from 928intl. After talking with Greg Brown, decided to replace them with the original style lock nuts.
Agree about the torque wrenches, but could they really be THAT far off?
The base of the threads is particularly vulnerable to this problem and if the piece were to be heated to degass the hydrogen formed immediately after electro plating such problem may not have happened. This all pre-supposes that hydrogen embrittlement is the issue and at the moment that has yet to be proven- just a consideration at this stage.
A down n dirty check shows the wrench is a couple pounds off. Showing my work,
The sand bag is 17.2lbs, distance from wrench head-square to cap is 16in converted to 1.33ft yields 22.93ft/lb.
On the bench vise with the wrench set to 23ft/lbs, the bag pulls it to 24ft/lbs.
So roughly 1ft/lbs off at that particular setting.
My goal on this ball joint nut was 88ft/lbs (120Nm), roughly 4 times my reference check. Am I clear logically that the wrench may be @4ft/lbs off at that higher setting?
And is that enough to snap the stud?
Apologies to the more informed, just trying to work through this
A down n dirty check shows the wrench is a couple pounds off. Showing my work,
The sand bag is 17.2lbs, distance from wrench head-square to cap is 16in converted to 1.33ft yields 22.93ft/lb.
On the bench vise with the wrench set to 23ft/lbs, the bag pulls it to 24ft/lbs.
So roughly 1ft/lbs off at that particular setting.
My goal on this ball joint nut was 88ft/lbs (120Nm), roughly 4 times my reference check. Am I clear logically that the wrench may be @4ft/lbs off at that higher setting?
And is that enough to snap the stud?
Apologies to the more informed, just trying to work through this
The torque wrench may not be off in a pure linear way.
Why don't you bring it by and we will check it against a couple of my torque wrenches.
You can also see your engine pieces....fresh from the machine shop.
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The days of free technical advice are over.
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My goal on this ball joint nut was 88ft/lbs (120Nm), roughly 4 times my reference check. Am I clear logically that the wrench may be @4ft/lbs off at that higher setting?
And is that enough to snap the stud?
Apologies to the more informed, just trying to work through this
Calibrations are much more meaningful when carried at the applied moment. That being said 4 ft lbs is neither here nor there in the bigger picture of things. I have no idea what your torque wrench manufacturer will claim for repeatability accuracy but I will bet it is not going to be better than 5% unless it is made for NASA.
High strength fasteners are used to reduce the size of the fastener [in this case the diameter of the bolt]. When making a design a mechanical engineer will not exceed 90% of yield under any circumstances and the design will likely rely on the joint operating in a stress range somewhere in the region of 50 to 70% of yield- this allows for variations due to load and temperature. Thus if the specified torque is 88ft lbs and you accidentally set it to 92 ft lbs you can be pretty sure it will not yield [i.e. plastically deform] yet alone snap. Thus if your experiment accurately translates to 88ft lbs I would say you did nothing to cause the failure by the applied load and thus something else had to be the problem.
Another little experiment you can try is to take your torque wrench to one of the rear most bolts on one of the lower front control arms and mark the nut relative to the stud. Start at 60 ft lbs and see if it pops [it should]. Then increase the setting by 10 ft lbs increments. You should be able to increase the applied torque without moving the nut up to the 88 ft lbs set point specified. At each step check to see if there is any sign of movement of the nut- if there is stop immediately this happens.
Caution: this does not apply to the front bolts on the LCA that have a lower set point value [for some reason]. Try putting 88 ft lbs on those and the bolt will yield.
If your torque wrench proves to be calibrated accurately [as seems likely] then there has to be something wrong with the bolt. That something similar has happened to two examples and that after an electroplating process should tell a story. If earlier corrosion has played a part then you should see signs of the corroded surface within the bolt at the line of fracture- I take it you have not seen such.
07-30-2017, 12:48 AM
LCA shock mount torque value ?
