# NHTSA Defect Petition DP78021
> **121 BRAKING SYSTEM, BRAKES LOCK UP** · Opened 1978-01-19 · Closed 1978-05-26
## Investigation
- **Action number:** DP78021
- **Type:** Defect Petition
- **Open date:** 1978-01-19
- **Close date:** 1978-05-26
- **Manufacturer:** Mack Trucks, Inc.
- **Affected makes:** MACK
- **Affected components:** SERVICE BRAKES, HYDRAULIC
- **Affected model years:** 1976
- **Affected (make, year) variants:** 1
## Summary

121 BRAKING SYSTEM, BRAKES LOCK UP

## Source
- [NHTSA ODI investigation page](https://www-odi.nhtsa.dot.gov/owners/SearchResults?searchType=ID&targetCategory=I&searchCriteria.nhtsa_ids=DP78021)
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