Do you need a cdl for a Ford F750?

The F750 is sold as a 26,000 lb. GVWR vehicle, but actually has 31,000 lb. axles. If it's registered as a 26,000 lb. vehicle, and is not loaded over 26,000 lbs., then no, you don't need a CDL. If it's loaded to a gross weight of over 26,000 lbs., or if it's registered and tagged as a GVW vehicle (or whatever your state's classification for a vehicle over 26,000 lbs. is), then yes, you do.

Now if it's not registered as a vehicle over 26,000 lbs., but you're towing a trailer with it which brings the Gross Combination Weight Rating to over 26,000 lbs., you will need a CDL - Class B if the weight rating of the vehicle in tow is 10,000 lbs. or less, Class A if the weight rating of the vehicle in tow is more than 10,000 lbs.

In any instance where it's transporting a quantity of hazardous materials which requires placarding, or is a bus designed to transport more than 15 persons (including the driver), you need a CDL with the appropriate endorsements, regardless of what weight class the vehicle is registered as. If it's registered as a 26,000 lb. GVWR vehicle, you would need a Class C CDL with passenger or hazmat endorsements. If it was registered as a 33,000 lb. GVWR vehicle, you would need a Class B CDL with passenger or hazmat endorsements.