|
|
|
|
|
The eBearing News
March 29, 2004
Fuso Wheel Hub Failures Prompt Recall Campaign
copyright © 2004 eBearing Inc.
Mitsubishi Fuso Truck & Bus (Japan, now 65% owned by DaimlerChrysler, 20% by Mitsubishi Motor, and 15%
owned by other Mitsubishi Group companies) is formally recalling at least 113,000 heavy trucks, buses
and tractor trailer units. The vast majority of the vehicles are in Japan, but an unknown number may have been
exported, said Fuso.
Driving the recall is Mitsubishi management's recent admission that a series of high-profile wheel-off
hub failures are in fact part of a larger problem the company has been hiding for more than a decade.
In addition, the company faces a widening array of civil and criminal investigations over allegations
it systematically covered up the failures, failed to report to the proper safety authorities, and
endangered the public. Japan's road safety authorities also charge Mitsubishi blamed the hub failures
on improperly torqued lug nuts, even after it found no evidence and in fact that all of its internal
engineering studies pointed to defective hubs.
Mitsubishi, many believe, was predisposed to covering up the Fuso hub failures to avoid further damaging
its image. The company's stature is still suffering from a massive recall in 2000-2001, involving over
two million vehicles, triggered by admissions it fraudulently covered up most customer complaints
for 20 years and ignored problems which should have prompted recalls.
The Fuso wheel hub at the center of this controversy was designed in 1983; it has since been through
five generations, or engineering change levels. The problem, or problems, causing it to fail were most
likely introduced in 1992 with the type "D" revision.
Violating Mitsubishi's own engineering change protocol, the "D" wheel hub was tested only under
laboratory conditions before finding its way into production. No dynamic or on-vehicle testing was done.
With the "D" unit, Mitsubishi has not yet made it clear whether the raw forging itself, the machining, or
both, changed. The company's now-available failure analyses seem to point toward both.
One failure analysis reviewed by eBearing suggests structural issues with the forging, implicating a raw
shape which was difficult to form, making it prone to voids and cross-section irregularities.
A separate analysis, however, points to a more common cause of wheel hub failures. This report indicated
stress fractures originate from the radius where the flange (where the studs are located, and where
the brakes and wheel are attached) portion meets the central hub section. Fractures originating in this
area can result from a too-thin cross section or from stress risers created by a too-tight machined
radius. Tool paths, production machine maintenance, improper setup and even suspension geometry can
be other contributing factors.
The hub, regardless, has a critical weakness and high potential for
wheel-off, the worst possible type of failure. In addition, as Mitsubishi now points out, the failure becomes
more likely as time and stresses accumulate. The company also says the failure is more likely to show
up in trucks and buses which do a lot of turning under load, even more so in those which regularly turn
sharply while maneuvering. These are the situations which put the most stresses on the flange section.
Pinpointing the "D" units is problematic. In fact, some reports indicated the problem exists with all
hubs except the original type "A" and the latest type "F" specifications. Fuso's recall obscures the issue
even further, blaming, "the metal hubs were defective because they had not been sufficiently melted."
Vehicles using the suspect hubs were built between 1992 and 1996, when the current "F" specification
was introduced.
A 1999 right front wheel-off involving a passenger bus in Hiroshima prompted the Transport Ministry to demand
an investigation. Mitsubishi's report stated, "There are no complaints about similar accidents, so no
preventive steps are necessary." At the time, however, authorities now know dealers had already informed
Mitsubishi of at least 20 other wheel-off incidends. Its report instead blamed improper wheel torque and
the company refused further action.
The problem might have been contained internally, but a wheel-off turned deadly and changed that forever.
In January 2002, a 300-pound tire and wheel assembly separated from a Fuso truck in Yokohama,
flew 150 feet and killed 29-year-old Shiho Okamoto as she walked down the sidewalk
pushing a baby carriage. Her two children were not seriously injured.
The public, civic and legal outrage sparked by Ms. Okamoto's death were the catalysts which eventually
exposed the extent of Fuso's problem. Mitsubishi had initially blamed too-loose lug nuts for the failure
which caused Ms. Okamoto's death, rejecting its own engineering report on the unit which indicated a
structural problem.
Tracing back, authorities discovered at least 50 unreported wheel-offs; 30 of them predating Ms. Okamoto's death.
In the 18 months after her she was killed, 20 more wheel-offs were reported.
Fuso had launched a campaign in 2002 to inspect and repair the trucks, although it was not reported
to Japan's transportation authorities. Approximately 75,000 trucks have been repaired under that program.
After Ms. Okamoto's death, Mitsubishi's Kitsuregawa Laboratory tested front hubs from 480 trucks. Active
cracks were found in 140 of them, or just under 30%. Three of the hubs were actively failing.
Authorities now charge the resulting report, submitted to the Ministry of Land, Infrastructure and Transport,
was illegally falsified to show the hub failures were always caused by improper maintenance.
The company's official position was also to reject the lab's findings and continue to blame
poor maintenance -- improperly torqued lug nuts -- until mid-2003, when it
began to admit some of the blame might be with the hub itself.
In October 2003, police raided Mitsubishi headquarters, a plant in Kawasaki, and its Kitsuregawa Laboratory.
They were raided again in January 2004 in a continuing criminal investigation likely to result in a wide
range of civil and criminal charges.
Fuso estimates the recall will cost at least $27 million on top of what it has already spent inspecting
and repairing hubs.
Public sentiment in Japan has turned against Mitsubishi, particularly because it at first refused to
accept responsibility for Ms. Okamoto's death or offer an apology, both considered
vitally important in Japan.
Wilfried Porth, President and CEO of Mitsubishi Fuso, recently met and tried to apologize to
the family, but was rejected. "I will never forgive you," said Ms.
Okamoto's mother, "Why didn't you recall your vehicles before my Shiho died?"
Yasuo Fukada, Chief Cabinet Secretary, said last week, "It was unacceptable that it took time between the accidents
and the decision to recall. They should have found out the cause of the accident promptly and taken measures.
The company's morals may come into question as well as whether the Transport Ministry has given proper instructions."
Fuso recently revealed it has yet another potential recall situation, this time involving rear wheel hubs.
|
|
|
printer-friendly version
|
|
- by Bruce A. Carr
from individual research,
tips and commercial sources.
Unauthorized reproduction is prohibited.
|
|
eBearing.com ... for everything that moves™
Entire contents Copyright 1999-2008, eBearing Inc. All rights reserved.
eBearing.com and "... for everything that moves" are registered
trademarks of eBearing Inc.
|
|
|
|
|
| |
eBearing.com ... for everything that moves™
Entire contents Copyright © 1999-2008, eBearing Inc. All rights reserved.
eBearing.com and "... for everything that moves" are registered trademarks of eBearing Inc.
|
|
|
