Missouri just must have experience as a mechanic or been properly trained and can show how to properly adjust. No card needed.
Always made me wonder, CA, OR, WA and many other states have pull offs to perform a brake and brake function test before proceeding Down Grade. Not gonna get a mechanic up there to adjust them for you if out and if bypass the stop lose braking are subject to multiple fines. So Fines for adjustments No Card or Fines and possibly accident lawsuit If do not. Not exactly a coin toss.
Your correct no card needed-now.
During the time of FHWA the rules were different. Starting in 1998 the federal rules regulating motor
carriers and involved maintenance were overhauled-including brakes and related repair. The FHWA
became FMCSA. By 10-1-2001 changed rules and all verbiage pertaining to new/old rules was changed.
Because major motor carriers lobbied the old rules were archaic originally drawn up by the old ICC
going back to the 30's. Back in those years there was a brake certification card although most never
acquired and rule was never enforced. The card was brought on by Teamsters along with other odds
and ends.
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Part of this regulation overhaul also had to do with the crazy rules individual states had on the books,
One such rule was in Conn. Driver had to prove he had night clothes on when off duty in sleeper.
No joke-rules like that were lobbied and abolished.