How much brake fluid should I put in my boat trailer actuator?

Your boat trailer actuator should be filled with DOT 3 or DOT 4 brake fluid (as specified by most manufacturers, including Tie Down, Titan, and Dexter). The actuator’s master cylinder must always remain full, with fluid level kept approximately ¼ inch below the reservoir fill opening to allow for thermal expansion.

Filling & Maintenance Guidelines:

• Do not overfill: Leave a small air gap at the top of the reservoir. Overfilling may cause pressure buildup and leaks.

• Use fresh brake fluid only: Old or contaminated fluid absorbs moisture and can lead to internal corrosion and brake failure.

• Check regularly: Inspect fluid level before each trip and top off as needed, especially after bleeding the brakes or replacing lines.

• Never mix fluid types: Use only the type recommended for your actuator (usually DOT 3 or DOT 4). Mixing fluids may damage seals and reduce braking efficiency.

• Bleeding required: Anytime you add a significant amount of fluid or open the hydraulic system, bleed the brakes to remove air.

Safety Note: Brake fluid can damage painted surfaces. Use a rag to catch spills, and immediately wipe off any fluid that contacts trailer paint or vehicle finishes.