Wheel studs

Oonrahnjay · January 18, 2015, 03:50:06 AM

Quote from: Ace on January 17, 2015, 07:30:46 PMAfter replacing all the studs, careful examination of the existing 8, by eye, revealed an obvious stretching of the threads on some but not all of the studs!
Old age as I was told by the shop, or the clown holding the air gun on too long?

Ace, with quality materials -- like used in these studs -- they're made to take a certain amount of stretch with elasticity. That's what makes the clamping force that keeps a wheel on. But they're also made to maintain their integrity -- IF they're treated right. Look at the wheel axles on the B-17's that are still flying; nobody says "they're old age -- probably stretched and gonna break" even though they've had a hard life because they've been treated carefully in maintenance and assembly.
Yes, we have old buses and they've been ridden hard and put away wet and they've had lots of changes of tires and wheels but if the studs had been treated correctly, they shouldn't be damaged.
I'm going with the clown holding the air gun too long as the issue on your studs. Maybe not once, maybe the damage you saw was a progression on many times treated badly. But, yeah, treated badly.

ccrider · January 19, 2015, 06:33:09 AM

Care to share the name of the shop you are obviously blackballing here, or keeping that to yourself?

luvrbus · January 19, 2015, 06:43:38 AM

If you think the guy stretched the studs with his impact you better check your wheels because you are not going to break a stud using aluminum wheels it will break the wheel first if the stud is in good shape to begin with BTDT I am not defending the guy either steel vs aluminum the steel wins every time

Ace · January 19, 2015, 06:45:03 AM

Yea it's a local shop and although the owner and I are friends, I'd rather not say. It's not entirely his fault. It's the hired help he keeps!

eagle19952 · January 19, 2015, 07:08:20 AM

Quote from: luvrbus on January 19, 2015, 06:43:38 AM
If you think the guy stretched the studs with his impact you better check your wheels because you are not going to break a stud using aluminum wheels it will break the wheel first if the stud is in good shape to begin with BTDT I am not defending the guy either steel vs aluminum the steel wins every time

i wondered about that too. I have seen an impact crush and deform an aluminium wheel long before it distorted/ruined the stud...

bevans6 · January 19, 2015, 07:43:41 AM

I was curious about this, so I did some math and looked up some stuff in some of my go-to resource material. The stud is basically a 1 1/8th stud with a 16 TPI thread, the spline is .81" nominal diameter as it presses through the hole. I ignored the nut on the hub side of the stud. Root diameter of the 1 1/8" thread is around 1.07", so it's cross section is around 0.9". A Grade 8 stud has a material strength of 130,000 PSI to yield ( the point of maximum stretch with no plastic deformations, basically) so that stud has a strength of 118,000 lbs before it will stretch permanently. Ten studs, 1.18 million lbs. The spline is smaller, .81" in diameter, so it's strength is just under 67,000 lbs. One would expect the stud to fail at the root of the splined section before the threaded portion would fail. One would not expect these studs to fail given the typical loads and torque from doing up wheel nuts.

So what is that torque? I couldn't find a torque/load chart that had 1.125 - 16 TPI, since it's not a SAE thread per se, so I looked up 1.125 - 12 TPI, which is an SAE standard. The torque to load for the 16 TPI would be slightly higher than for 12 TPI, but the torque with dry threads to induce the yield torque and maximum design clamp load in a 1.125" 12 TPI fastener is 1,440 ft lbs. In other words, you should be able to torque that stud to 1,440 ft lbs without damaging the threaded portion of the stud in any way.

Now, I really don't know why Ace's studs failed, but the research I have found is that a lot of failures come from under-tightened lugs rather than over tightened, particularly with aluminium rims. The loose wheel moves, the aluminium crushes out, the stud is subject to flexing, one lug a bit loose means the load on the adjacent lugs is higher than design, a small fatigue crack starting from corrosion or damage, and boom - lug falls off. With aluminium wheels, a too loose lug would often start with a too tight one, causing the aluminium to fail and crush out, as suggested by others here.

Interesting science to all of this. Edit; a good link: http://www.meaforensic.com/wheel-separation-investigation-metallurgical-expert-mark-bailey-mea-forensic

eagle19952 · January 19, 2015, 09:13:15 AM

A good well oiled and fed 1 inch air impact gun can put out 1600 to 1900 fp/torque. that would entail a 1 inch feed hose and a very large compressor.
The ones that I have been around are air adjustable for max/limit torque output. they can be regulated, one would hope that a good tire shop will have pre-set/limit the air to the gun.

bevans6 · January 19, 2015, 09:28:29 AM

Agreed on that. One thing I didn't mention is that if you torque the lug nut to say 1500 ft lbs, you will develop far more clamp load than is needed to rip the stud off the hub. The .810" diameter splined section will fail well before you exceed the plastic deformation capacity of the 1.125" wheel nut section of that stud. Interesting, and of course all other things being equal...

Brian

Oonrahnjay · January 19, 2015, 10:54:47 AM

Quote from: bevans6 on January 19, 2015, 07:43:41 AM... Interesting science to all of this.

Sure is! Thanks, Brian.

buswarrior · January 19, 2015, 12:24:14 PM

Somewhere in my collection, I have a couple of examples of stretched studs. The threads under the nut were leaning over, damaged from the high torque, and the stud is noticeably skinnier further down its length, such that you wouldn't be able to run the nut down there properly.

The natural elasticity of the stud is what gives us the clamping force to hold the wheel and let's the stud take road shocks. Stretch it, and it won't stay tight, and can't withstand road shocks as well. Elasticity in our studs is our friend!

Remember, the tire tech may have turned the gun UP to remove the last set of stubborn fasteners and forgotten...

happy coaching!
buswarrior

Ace · January 19, 2015, 12:39:33 PM

Okay not sure the why, or whats, but I do know there's only been one to remove the wheels on different occasions since I've owned the bus so the where and who are known!
It's water over the dam and I'm not wanting to lose a friend over stupidity on another so it is what it is and that was a costly error on not only their part but mine too for trusting they (he) would do it right! It won't happen again, that's for sure!
Here's a bad pic of the studs broke off and you can see how HE stuck the nut covers back on using tub and tile caulking and half of them left the wheel too!
Plain and simple, it was a mess!

Ace · January 19, 2015, 12:48:28 PM

Let me also add this is the same guy that rung off the studs of one air bag using an air gun when replacing it. THAT he paid for because I was standing there. He's the same guy that while changing said air bags, took the plastic air line and folded it over and squeezed it with vise grips to keep it from leaking down. Had I not been there, he would of put it back together but I told the boss and he made him replace all those lines! Pure ignorance!

Oonrahnjay · January 19, 2015, 03:52:20 PM

Quote from: Ace on January 19, 2015, 12:48:28 PM... Pure ignorance!

Yeah, Ace, ignorant and sloppy (and I guess lazy if he tries to stick his broken mistakes on with caulk). Bad combo.

Ace · January 19, 2015, 04:57:51 PM

Don't get confused. The caulking was to hold the lug nut covers on the lug nuts, not the broken studs! The studs broke during travel and there went the covers as well as a few others where the studs didn't break!