# NHTSA Preliminary Evaluation PE86073
> **INEFFECTIVE AIR BRAKES** · Opened 1986-08-13 · Closed 1986-10-16
## Investigation
- **Action number:** PE86073
- **Type:** Preliminary Evaluation
- **Open date:** 1986-08-13
- **Close date:** 1986-10-16
- **Manufacturer:** General Motors, LLC
- **Affected makes:** CHEVROLET; GMC
- **Affected components:** SERVICE BRAKES, HYDRAULIC
- **Affected model years:** 1984, 1985, 1986
- **Affected (make, year) variants:** 6
## Summary

SUMMARY OF INFORMATION FROM MANUFACTURER:NONE AT THIS TIME.ANALYSIS:A PNEUMATIC BALANCE TEST PERFORMED ON FOUR OF THE SUBJECT BUSESBY AFTERMARKET BRAKE SYSTEM DISTRIBUTOR INDICATED THAT DURING A 15 PSIBRAKE APPLICATION, THERE WOULD BE 15 PSI AT THE FRONT AXLE AND 0 PSI ATTHE REAR.ONE OF THE KEYS TO BRAKE BALANCE IS BRAKE ACTUATION AND RELEASE.THE REAR SHOULD APPLY BEFORE THE FRONT AND RELEASE SLIGHTLY AFTER.SINCEMOST BRAKING OCCURS BELOW 20 PSI, IT WOULD SEEM THAT HAVING THE SAME ORCLOSE PRESSURE IN ALL CHAMBERS IS IMPORTANT FOR PROPER BALANCE.PROPOSED ACTION:OPEN A PE.SEND AN IR.

## Source
- [NHTSA ODI investigation page](https://www-odi.nhtsa.dot.gov/owners/SearchResults?searchType=ID&targetCategory=I&searchCriteria.nhtsa_ids=PE86073)
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