Brake Fluid for Commercial Vehicles
For the vast majority of vehicles, a single fluid - brake fluid - is used in both the clutch and brake reservoirs. Check the cap of your clutch fluid reservoir - it should indicate if you need a special fluid.
Brake fluid should be changed every 1 or 2 years. Over time, moisture diffuses into the fluid through brake hoses and rubber seals, increasing the water content. If your brake fluid is low, you probably have a problem such as a leak. Leaks and excessive moisture in the fluid can both result is a loss of hydraulic pressure and braking ability, so it's as well to check and change your fluid periodically.
You can find which DOT your vehicle requires, normally in your handbook. However if you're not sure, or you have a unique or race vehicle contact the Opie experts for Brake Fluid advice.