Make sure to call ahead and ask if the lower-level "Schaudepot" is open on the day you visit. Half of the cars are in there (less than 50 in total), and it's sometimes closed for rearrangement. Like it was for me, last week.
Oh, and when you're there make sure to visit the Maritime Museum just round the corner. I have zero interest in anything maritime (or so I thought), but that is perhaps the greatest museum I've visited (3 times so far).
Another oh: Hamburg's (arguably Germany's) biggest tourist attraction, the Miniatur Wunderland, is also round the next corner... : )
Great article, thanks for the tip. I contacted them about a Borgward racing car from the 1950's but they said it is no longer in the collection. Borgward, Hansa and Goliath - all part of the Borgward group - were manufactured down the road in Bremen, until the company was shuttered by the government to pay off loans. A very questionable move, especially as the 1.5 liter Borgward was the most powerful engine meeting the new F1 specs of 1961. But racing was a hobby at Borgward compared to Porsche and Mercedes (before 1955).