Buick Regal Forum : “my car won't go in reverse until it's warm, do i need a new trans or can it be f...”

First check fluid level.

your problem is most likely either a slipping gear in the transmission that once it warms up expands enough to grip the opposing gear, or it simply does not have enough fluid. either way take it to a transmission shop first, make sure to get quotes from different people if it is not a simple fix, its also possible that the issue is the rear end of the car, if i remember right the 85's are rear wheel drive if so it is also possible that the reverse side of your pinion gear is damaged