What difference, if any, is there between a warning device and a warning signal?

Section § 393.51: Warning signals, air pressure and vacuum gauges.

Question 5: What difference, if any, is there between a warning device and a warning signal?

Guidance: For purposes of §393.51, the terms may be used interchangeably.

Is a warning device required in a Commercial Motor Vehicle (CMV) with a single hydraulic brake system which uses the driveline parking brake as the emergency brake system?

Section § 393.51: Warning signals, air pressure and vacuum gauges.

Question 4: Is a warning device required in a Commercial Motor Vehicle (CMV) with a single hydraulic brake system which uses the driveline parking brake as the emergency brake system?

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Are vacuum gauges required on the vacuum portion of vacuum-assisted hydraulic brakes?

Section § 393.51: Warning signals, air pressure and vacuum gauges.

Question 3: Are vacuum gauges required on the vacuum portion of vacuum-assisted hydraulic brakes?

Guidance: No. Section 393.51(d)(2) requires only that CMVs with vacuum brakes (not...

Is the vacuum portion of vacuum-assisted hydraulic brake systems required to have a warning device?

393.51: Warning signals, air pressure and vacuum gauges.

Question 2: Is the vacuum portion of vacuum-assisted hydraulic brake systems required to have a warning device?

Guidance: No. Only the hydraulic portion of vacuum-assisted hydraulic brake systems is...

Is the low pressure warning device required to activate before the tractor protection valve?

Section § 393.51: Warning signals, air pressure and vacuum gauges.

Question 1: Is the low pressure warning device required to activate before the tractor protection valve?

Guidance: No. Section 393.51 does not explicitly require the warning device to...

Are the brakes on a vehicle towed in a driveaway-towaway operation or towed disabled vehicle required to be operable at all times?

Section § 393.48: Brakes to be operative.

Question 3: Are the brakes on a vehicle towed in a driveaway-towaway operation or towed disabled vehicle required to be operable at all times?

Guidance: Section 393.48(c) provides an exception to the requirement...

If a truck or truck tractor manufactured prior to July 25, 1980, and having 3 or more axles, has inoperable brakes on the front axle or some of the brake components are missing, would the vehicle be in violation of § 393.48?

Section § 393.48: Brakes to be operative.

Question 2: If a truck or truck tractor manufactured prior to July 25, 1980, and having 3 or more axles, has inoperable brakes on the front axle or some of the brake components are missing, would the vehicle be in violation...

If a CMV manufactured on or after July 25, 1980 (see § 393.42) has brake components on the front axle, and the brakes are not operable, does the vehicle comply with § 393.48?

Section § 393.48: Brakes to be operative.

Question 1: If a CMV manufactured on or after July 25, 1980 (see § 393.42) has brake components on the front axle, and the brakes are not operable, does the vehicle comply with § 393.48?

Does the term ‘‘rear wheels’’ include the tag axle on a bus/motorcoach?

Section § 393.44: Front brake lines, protection.

Question 1: Does the term ‘‘rear wheels’’ include the tag axle on a bus/motorcoach?

Guidance: Yes. The braking system on a bus/motorcoach must be constructed so that if any brake line to either front wheel...

Are tractor protection valves required by § 393.43(b), or may similar devices be used?

Section § 393.43: Breakaway and emergency braking.

Question 1: Are tractor protection valves required by § 393.43(b), or may similar devices be used?

Guidance: No. Similar devices may be used provided the devices meet the performance requirements of § 393...