Denial of Motor Vehicle Defect Petition

Topics:  Jeep Grand Cherokee

Kenneth N. Weinstein
National Highway Traffic Safety Administration
February 6, 1998

[Federal Register: February 6, 1998 (Volume 63, Number 25)]
[Notices]               
[Page 6255]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr06fe98-154]

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DEPARTMENT OF TRANSPORTATION

National Highway Traffic Safety Administration

 
Denial of Motor Vehicle Defect Petition

AGENCY: National Highway Traffic Safety Administration (NHTSA), 
Department of Transportation.

ACTION: Denial of petition for a defect investigation.

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SUMMARY: This notice sets forth the reasons for the denial of a 
petition submitted to NHTSA under 49 U.S.C. 30162, requesting that the 
agency commence a proceeding to determine the existence of a defect 
related to motor vehicle safety.

FOR FURTHER INFORMATION CONTACT: Dr. George Chiang, Office of Defects 
Investigation, NHTSA, 400 Seventh Street, SW, Washington, DC 20590. 
Telephone: (202) 366-5206.

SUPPLEMENTARY INFORMATION: Mr. and Mrs. Scott Montreuil of Ramsey, 
Minnesota, submitted a petition dated October 1, 1997, requesting that 
an investigation be initiated to determine whether 1993 Chrysler Jeep 
Grand Cherokees contain a defect related to motor vehicle safety within 
the meaning of 49 U.S.C. Chapter 301. The petition alleges that 1993 
Chrysler Jeep Grand Cherokees have a defective viscous coupling that 
could cause the steering to bind and lock up, and possibly affect the 
vehicle's braking.
    Although not all Jeep Grand Cherokees utilize a viscous coupling, 
some 1993 through 1995 Jeep Grand Cherokees are equipped with a Quadra-
Trac transfer case. An integral part of the Quadra-Trac transfer case 
is its viscous coupling, a speed-sensitive device that controls torque 
output between the front and rear drive shafts. The housing of the 
viscous coupling contains high viscosity silicone fluid and specially 
engineered metal plates splined alternately to an inner and outer drum. 
When there is a difference in front-to-rear axle speed, such as when 
the rear wheels slip, the resulting friction between the metal plates 
increases the temperature inside the unit. This causes the fluid to 
expand, building pressure that moves the plates together. This occurs 
almost instantaneously in two modes: the ``shear'' mode, when momentary 
speed differences occur such as in cornering or tight turns, causing 
the plates to move near each other, or the ``hump'' mode, when high-
speed differences occur for a longer period of time, such as in deep 
snow or on off-road trails, causing the plates to lock and the front 
and rear drive shafts to turn at the same speed for maximum traction. 
As traction is gained, the fluid cools, and the plates separate.
    When the viscous coupling fails, it may remain in one of the above 
two modes all the time, regardless of whether there is a difference 
between front-and-rear axle speed. If the coupling fails in the 
``hump'' mode on dry pavement, it may cause vehicle hopping/bucking 
during turns, resulting in rapid wear of tires.
    NHTSA drove a Jeep Grand Cherokee with a simulated failure of the 
viscous coupling in the ``hump'' mode on dry pavement at various 
speeds. Some hopping/bucking was experienced while the vehicle executed 
turns. However, no steering or braking problems were experienced at any 
time.
    A review of agency data files, including information reported to 
the Auto Safety Hotline by consumers, indicated that, aside from the 
petition, there were no other reports concerning failure or malfunction 
of the viscous coupling in 1993 Jeep Grand Cherokees. There was a 
report pertaining to transmission lockup when the engine was started, 
but this was not related to a failure of the viscous coupling.
    Chrysler Corporation has received 40 complaints concerning failure 
or malfunction of the viscous coupling in the transfer case of 1993 
Jeep Grand Cherokees. Five of these complaints report handling 
problems, such as vehicle hopping during turns. The remaining 35 
complaints are solely related to financial assistance issues. No 
crashes or injuries were reported.
    The agency has analyzed available information concerning the 
problem alleged in the petition. Based on its understanding of viscous 
couplings, NHTSA believes that the failure or malfunction of the 
viscous coupling in the subject vehicles cannot cause lockup of the 
steering or adversely affect the brake system.
    For the reasons presented above, it is unlikely that NHTSA would 
issue an order for the notification and remedy of a safety-related 
defect in the subject vehicles at the conclusion of the investigation 
requested in the petition. Therefore, in view of the need to allocate 
and prioritize NHTSA's limited resources to best accomplish the 
agency's safety mission, the petition is denied.

    Authority: 49 U.S.C. 30162(d); delegations of authority at CFR 
1.50 and 501.8.

    Issued on: January 26, 1998.
Kenneth N. Weinstein,
Associate Administrator for Safety Assurance.
[FR Doc. 98-2937 Filed 2-5-98; 8:45 am]
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