In Chapter 16 of The Grapes of Wrath, the Wilson's car breaks down again, and Tom suggests that he and Casy stay behind to fix it (it needs a bearing, which they will have to wait to buy on Monday). So, the truck will go ahead to California while the car stays behind a couple of days. Everyone likes this idea except Ma. She threatens to fight Pa with the jack handle if he agrees to this plan. She says:
"All we got is the family unbroke."
Ma refuses to break up the family any more than it's been broken up. The family has already left Grandpa behind. Ma has seen what has happened to the Wilsons because of car trouble: they've been delayed by weeks and had their family broken up too (Wilson's brother had car trouble and couldn't make the trip). No, Ma doesn't care about going to California; she doesn't care about money, or jobs, or opportunity. All she cares about is the family: she's the glue that holds them together:
"Up ahead they's a thousan' lives we might live, but when it comes it'll on'y be one."