I'm posting this here and on BrassGoggles, in the interests of crossover fairness..
I reckon that The Airship (I think it needs capital letters) is a fundamental part of both Dieselpunk and Steampunk - whether the ornate Victorian kind or the sleek and majestic Zepplin. Is there anything else?
Good question. I think a fascination with modes of travel - by ship, by train - are shared by both, although there are clearly differences in what that looks like in each context.
Are you asking about which common tropes cross over between the two styles?
I'd say the entire 1910s was a soft period between the two, so you would have:
I'd say that they have the whole Industrial Revolution in common. Both genres inherit the scifi focus on technology. In steampunk, machines have gone beyond the prototype stage, and their users have decorated them to show off artistic skills as well as mechanical skills. In dieselpunk, we take another step and hide the function behind the elegance of the form. In both cases, however, the machines have gone from occasional tools to transformative elements that change our lifestyles. For instance, gas lights and neon lights have different infrastructures and designs, but they both make it possible to function without sunlight--that was only possible before with candles, torches, and lanterns, all with exhaustible fuel.
not being an expert at all ;) but what links both should be the punk attitude!
Steam Trains are definately a crossover technology, as they persisted up until the early Atomic era. While "Streamliners" are total Dieselpunk, the more rough and rugged non-streamline "riveted cans" were still being built in the 1950s.
Coal-burning steam electrical generators are still in use today.
Speaking of electricity, "Teslapunk" type stuff is a big crossover area with big honking lightening-arcing Tesla Coils and spark gap generators a common "mood setting" technology in both areas. The Mad Scientist archetype in general starting with Viktor Frankenstein as Shelley designed him up to the "Evil Tesla" archetype perpetuated in the cinema.
Telephones. The "old fashioned" wall hangers with the fixed mouthpiece and ear horn on the wire lasted from Victorian era up into the 1920s. In general it was the "internet" of its day until Wireless stole the show in the Diesel era. Wireless can cross backwards into Steampunk as well.
Culture too: Ragtime music and Tin Pan Alley type stuff are borne in that 1900's/1910's transitional period and fit both areas equally. Old Time music transitioned from African-American work songs and Scots-Irish folk balads of the Steam Era through the Piedmont and Delta sounds that informed Blues and early Country and Folk of the Diesel era and eventually morphed into Bluegrass and Country and Blues and Rock.
Vaudeville was born in Steam and perisited well into Diesel. The circus and the sideshow were still the main forms of entertainment for those who lived away from major cities and add a creepy punk vibe to either area.