Investigation EA84027: Vehicles

Status

CLOSED

Opened

Aug 28, 1984

Closed

Sep 4, 1987

Model years

—

Subject

Rear brake lockup

Summary

Summary: the proportioning valve was changed for 1983 models (470 psi to250 psi split point) to reduce rear brake torque. Gm claims that brakingperformance may be limited by tire traction on an unloaded vehicle withnew unburnished linings, but braking balance improves once the liningshave been burnished as a result of normal use.analysis: testing at etf shows that braking performance of an unloadedvehicle was improved by use of the 1983 proportioning valve but brakingefficiency with the 1982 configuration appeared to be acceptable (79% to90% on low friction surfaces).status: closed 9/4/87.===

An NHTSA investigation looks into whether a safety defect exists. Opening one is not a finding. Outcomes can include a recall, closure without action, or further inquiry.