WARNING:  The brake system could be affected if the brake fluid level is below the MIN mark or above the MAX mark on the brake fluid reservoir.
  WARNING:  Do not use any fluid other than the recommended brake fluid as this will reduce brake efficiency. Use of incorrect fluid could result in the loss of vehicle control, serious personal injury or death.
  WARNING:  Only use brake fluid from a sealed container. Contamination with dirt, water, petroleum products or other materials may result in brake system damage or failure. Failure to adhere to this warning could result in the loss of vehicle control, serious personal injury or death.

Hydromax
Chassis with gross vehicle weight ratings of 20500 pounds (9299 kilograms), 22000 pounds (9979 kilograms), 24000 pounds (10886 kilograms) and 26000 pounds (11793 kilograms) come with Hydromax Brake Booster Systems. Use Motorcraft DOT 5.1 Motor Vehicle Brake Fluid or equivalent meeting Specification WSS-M6C65-A3. See  Capacities and Specifications . 
Add fluid up to the bottom of the rings at the top of the reservoir. Do not fill above this line.
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  • Use only DOT 5.1 brake fluid certified to meet our specifications.
  • A clear gel-like substance in the hydraulic brake master cylinder reservoir could appear on some vehicles. This substance is a silicone base lubricant used during assembly of the master cylinder. It floats on top of the brake hydraulic fluid in the master cylinder. This condition is normal and in no way affects the operation of the brake system. It does not require any service.
  • Replace brake system fluid on a regular basis to maintain optimum braking performance, especially under heavy-duty driving conditions such as frequent steep slopes or heavy towing loads.   See   Scheduled Maintenance
Hydroboost
Chassis with gross vehicle weight ratings of 16000 pounds (7257 kilograms), 18000 pounds (8165 kilograms) and 19500 pounds (8845 kilograms) come with Hydroboost Brake Booster Systems. Use Motorcraft DOT 5.1 Motor Vehicle Brake Fluid or equivalent meeting Specification WSS-M6C65-A3. See  Capacities and Specifications . 
Add brake fluid from a clean, unopened container until the level reaches MAX. Do not fill above this line. Use only DOT 5.1 brake fluid that is certified to meet our specifications.
Replace brake system fluid on a regular basis to maintain optimum braking performance, especially under heavy-duty driving conditions such as frequent steep slopes or heavy towing loads.   See   Scheduled Maintenance