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In the ongoing saga of the two bolts that GM says that I need to remove the windshield to get at...
I cracked open my old text book.
The only threads doing any holding are the ones inside the nut.
Excess thread beyond the nut does nothing. Only the engaged threads matter.
The video that got me worried about cutting them to remove them:
His contention is that the extra thread somehow catches again after enough force is applied to strip the threads from the start position.
I don't think he knows what he's on about because he keeps saying shear. The shear force will be at the plane where the two parts meet and will break the bolt there; not cause it to slip down the nut. Threads strip in tension.
If GM had really "highly engineered" this with the idea that an extra 1/4" of thread was going to grab after the engaged thread stripped; there'd be another nut on the end of the threads as a stop.
My contention is this design decision was made to force the customer to go to the dealer to get the evaporator replaced because small shops don't have the ability to remove the glass.
But if you're really worried...
Cut the original bolt.
Replace it with all-thread rod.
Tighten it to spec with a nut at the top and use red Loctite® on that nut.
That would replicate the OE bolt.
PS: Royalty Auto Services is the only source for this worry I can find. Google cites them in the top three hits when you search for the issue. Sorry, search for this non-issue.
PPS: The engineers that designed this are also the ones that lied about why they use torque to yield fasteners. ARP proves them wrong over and over with regards of getting consistent torque. Torque to yield is so a machine can do the torquing. They're very good at counting degrees of rotation but not so much at measuring torque when you have a bolting fixture that does all of the head bolts at the same time.
PPPS: If GM designed this all to collapse in such a way to put those bolts in tension during a collision, I think anyone injured in such an accident has an excellent case for substantial financial compensation.
The car is engineered for ease of assembly, by less than genius individuals on an assembly line that costs millions per minute to operate.... That bolt is ordered by the truckload. That bolt may be the same bolt as a suspension bolt. The less part numbers in inventory the better from an accounting standpoint.
ReplyDeleteI would be more inclined to cut the existing bolt and sneak it out with a pry bar than replace it with all thread. That's probably a hardened bolt and odds are that it's metric. Try finding hardened metric allthread. Cut the extra bolt threads off. I promise you this: the flat rate techs at the dealership are cutting that bolt to work on the ac.
I suspect, with the tip shape and the excessive length that you are correct that it's intended to speed assembly rather than some nebulous crash safety feature.
DeleteI know where to get hardened metric all-thread! I still have contacts from when I helped reverse engineer an O2 manifold to let a Mirage III take Phantom II parts.
Come to think on it... The fact they come in from the top and not from the bottom really reinforces your notion that they're the way they are for assembly speed by the "highly trained" UAW line ape.
DeleteHighly trained? You should've given a keyboard alert before typing that. Glad I wasn't sipping a beverage.
DeleteI thought a line ape was a USMC rifleman.
DeleteI've been told that my sense of humor is so dry and cynical it can be used as a dessicant.
DeleteHowever, I do like house pets. Mostly because they can't snitch
Delete