Pension and other securities

Hi, I am recently unemployed and have been looking at the possibitlity at getting a car for work and education purposes. My income is unemployment. My Grandpa would be more than willing to co-sign on a car loan for me, but he is very afraid of loosing his pension and social security. If he co-signs, could he be at risk for loosing these incomes? Of course, I wouldn't want to put him in this situation if I defaulted. His pension is with the MTA bus company.