<VV> Anti-seize on wheel nuts

[J Bruce Weeks]

Yeah, it was both a high and low point in my career to be called before the NHSTA board. It started after several deaths in a three-month time span from flying wheels. The investigation was titled something like "Wheel Fastener Design Inadequacies." or some such. It quickly moved away from that as it became obvious from the data that the wheels will stay on if properly maintained. Some were written off to poor maintenance, bearing failures, driver error, etc. The finding stated that the designs were adequate but that the requirements for retorquing the wheel nuts varied widely between manufacturers. So we were charged to come up with an industry standard from the manufacturer's side. The fleets, however, did not want to retorque so soon because they were union shops and only a mechanic at a depot could do the work. The fleets wanted us to push the retorque requirement out to 600-700 miles. It needed to be much sooner, closer to 125-150 miles. Only way to increase the interval would be to use a much higher initial torque which would exceed the studs' strength. The main issue is that there is always something in the joint that gets worn away during initial operation: paint, rust, dirt, etc. a 22 mm wheel stud is stretched 0.021" at 550 ft-lbs of torque. Paint is specified not to exceed 0.007". Take a dual wheel set and you have four paint surfaces on two wheels plus two brake drum faces that's 6 X 0.007" = 0.042! Twice the stud stretch.  With flat face wheels (as opposed to the old Budd mount system with ball seat nuts) wheels are held in place as if they are a fully engaged clutch. The "pressure" developed by the stud tension clamps the clutch together with enough force to resist slippage at the face during full brake lock-up. It takes 350 ft-lbs minimum WITH A NEW SYSTEM. Once rusty or if hardened anti-seize clogs the threads, the torque to achieve correct tension goes up, sometimes by a lot. But the mechanic can only measure torque. So he clicks his wrench and walks away. In about 250-300 miles, measurable nut torque has dropped by 50%. And so has the stud tension. It is then below required clamp load. The wheels slip a bit during braking, abrade more material out of the joint and you know where it goes from there. Thus the need for clean, lightly lubricated threads and a retorque interval of about 150 miles. J. Bruce Weeks, 
 
      From: Jim Becker <mr.jebecker at gmail.com>
 To: J Bruce Weeks <jbruceweeks at yahoo.com>; virtualvairs at corvair.org 
 Sent: Wednesday, February 11, 2015 12:08 PM
 Subject: Re: <VV> Anti-seize on wheel nuts
   
That is a disturbingly high percentage.  If you consider that a brake job 
(or new set of tires or whatever) on the typical tractor involves 10 "truck 
wheel end disturbances ", that means that 1 in 50 will loose a wheel.  With 
10 million large trucks in this country, if half (or even a quarter) of them 
get their wheels disturbed in a year, you are talking about a lot of flying 
wheels every day.

Jim Becker

-----Original Message----- 
From: J Bruce Weeks via VirtualVairs
Sent: Wednesday, February 11, 2015 5:33 AM
To: virtualvairs at corvair.org
Subject:  Anti-seize on wheel nuts


Only 0.2% of truck wheel end disturbances (any reason a wheel is removed and 
replaced) at the time resulted in a wheel-off. 98% of those wheel-offs 
occurred within 600 miles.