Technically, you can purchase anything you want during your divorce case. The more important question would be… what are the consequences of making a major purchase during my case? The answer to this question depends on a number of different factors, including the Judge assigned to your case, the county your case is being heard in, and the amount of assets you have.
In St. Louis County, there are local rules that go into effect upon the filing of the case. These rules, listed as local rule 68.3, include restrictions on finances including not making any extraordinary purchases or spending down any accounts. Other counties have varying versions of this rule.
So what do you do if your car dies during your case? The easiest thing is for your attorney to reach out to opposing counsel and negotiate for a car to be purchased by consent. You could also file a Motion with the Court asking the Judge to allow for a major purchase. The worst option would be to just go buy a car without consent or Court approval. This decision could negatively impact your case as the Judge might choose to compensate your spouse for your decision or you could be sanctioned by the Judge.