My Volvo excavator is experiencing the same problem. I have to keep the brake on all the time to keep the machine in a safe position. Then I spoke with a friend who works in a used Volvo equipment store. He said that it's the lever lock, and it won't stay locked in the locked position, so that's why I have to keep the break all the time; this causes the machine to clunk into gear when I'm reversing because the lever lock is holding the lever down, causing the engine to try to go into gear. So You'll need joysticks to operate the lever lock. Thank you.