Gladhands and Trailer Air Lines: How to Find and Fix Air Leaks

Gladhands connect the tractor's air system to the trailer. There are two: the service line (blue), which carries the air for applying the brakes, and the emergency or supply line (red), which charges the trailer system and releases the spring brakes. A leak at either one can cause slow brake release, poor braking or trailer brakes dragging.

Common causes of air leaks

• Worn or cracked gladhand seals — the most common cause, especially in cold weather when rubber hardens.
• Damaged gladhand bodies — bent or cracked from being dropped or driven over.
• Chafed or cracked air lines — lines that rub on the deck plate or frame.
• Loose fittings — at the gladhand or the trailer bulkhead.

How to find a leak

1. Connect the lines and build full air pressure.
2. Listen for hissing around the gladhands and fittings.
3. Spray soapy water on connections — bubbles show the leak.
4. Check the lines along their full length for cracks and rub marks.

Winter tips

• Replace hard or flattened seals before winter.
• Keep dust caps on unused gladhands so moisture and dirt stay out.
• Support lines so they do not drag or rub.

Frequently asked questions

Which gladhand is blue and which is red?
Blue is the service (control) line. Red is the emergency (supply) line.

How often should gladhand seals be replaced?
Replace them whenever they are cracked, hard or flattened. Many fleets replace them as a routine winter item.

Why do my trailer brakes drag?
Possible causes include an air leak on the emergency line, a faulty valve or brakes out of adjustment. Check for leaks first.

Air parts we carry

Shop the Automann Blue Service Gladhand and the Automann Tire Inflator with Gladhand, or browse the Truck Parts collection.

Related guides: Winter Air Brake Maintenance · Truck Air Brake Basics

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