<VV> Fuel Leak

[Joel McGregor]

Since I recently bought a large truck I've done a lot of reading on this.  Hugo is mostly right except wheel loss is an issue in the US also since trucks switched to all RH threads.   BUT the thread switch wasn't the problem.  The system with RH and LH threads on large trucks with dual wheels is commonly called Budd or lug center.  They have tapered seats that center the wheel and the hub center system has all RH threads BUT this still isn't the issue.  The problem was created because the old Budd system clamped each wheel sepearately and the new system clamps both wheels at the same time.  As Hugo mentioned this creates a whole stack of surfaces clamped together in the new system.  Hub to drum, drum to inner wheel, inner wheel to outer wheel and outer wheel to lug nut washer.  (No tapered seats on hub center systems)  Any paint, dirt, rust or whatever will cause so much change in thickness when it settles it exceeds the amount of stretch the stud has to clamp with.  I have read that here it is drilled into any truck driver that wheels must be re-torqued within something like 100 miles after any service.  I saw a wheel change reciept recently and it had a warning hand written on it to re-torque the wheel within 100 miles.
Oiling threads is a good thing and will give a more accurate stretch.  Torque has to be adjusted for oiled threads.  Rod bolts are always supposed to be oiled and they get some crazy stresses without coming loose.
Whatever force that loosens the nuts on one side only matters in making them fall off after they are already loose.  It isn't enough to make any difference on a tight nut.
I use anti-seize on my truck but it has the old Budd system.  It's a 1997 model.
BTW he didn't say to only tighten the greased fittings finger tight.

Joel McGregor



-------- Original message --------
From: roboman91324--- via VirtualVairs <virtualvairs at corvair.org>
Date: 9/27/18 10:21 PM (GMT-06:00)
To: Hugo at aruncoaches.co.uk, virtualvairs at corvair.org
Subject: Re: <VV> Fuel Leak

Hugo,

Please excuse my last post.  Mechanical precession is exactly what is going on with left-side lug nut loosening.  I assumed you were talking about precession as it pertains to the dynamics of rotating mass.  I. E. gyroscopic precession.  I have always known it as epicyclic fretting.

By the way, mechanical precession is still a concern but the deeper tapered lug nuts added just enough friction to compensate.  In addition, the taper (acorn) itself, not just the added contact area, has been the solution to the issue in two ways.  First, the taper acts as a wedge which increases the applied force "N" in the frictional force equation.  Second, the taper allows for different diameters at different points of contact.  These interesting tricks of Physics were a game changer.

Again, my apologies,

Doc

PS:  I believe the rest of my posts to be accurate but you never know.
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