Yesterday I was moving 5 tons of crushed gravel and leveling some areas around driveway project etc. I have it in 4 low most of the time. Anyway after waiting for the mini ex operator to pile up some crap clay dirt and rocks I went in a grabbed a big scoop and took off to dump it about 200 feet away. I noticed the tractor struggling more then normal. When I got back to get the next load I noticed the parking brake was on. I popped it off and all was well again. I did this twice. My question is simple how can I adjust them so it just don't go, or is is this normal? Here is some of what I was moving and grading.