Green’s Dictionary of Slang

1. (US) of machinery, out of order.

1914

Ade ‘The New Fable of What Transpires’ in Ade’s Fables 143: A Good Woman was a Jewel, but if one of them got a fair Run and Jump at a Check-Book she could put the National City Bank on the Hummer.

2. (US) at a disadvantage.

1912		R.W. Brown ‘Word-List From Western Indiana’ in DN III:viii 584: on the hummer, adv. At a disadvantage. ‘I’ve got him on the hummer and he knows it.’.
1920		Ade Hand-made Fables 29: Between the two of them it was the work of about an Hour to put most of the Old Families on the Hummer.

3. (US tramp) travelling on freight trains; thus living as a tramp [? SE humming along].

1919		D. Runyon ‘A Tale of two Fists’ XVIII in Pittsburgh Press (PA) 21 May 27/1: It might shock the promoters to see a $300 fighter come into town ‘on the hummer’.
1927		C. Sandburg ‘A.R.U.’ in Amer. Songbag 191: Been on the hummer since ninety-four.
1930		‘Dean Stiff’ Milk and Honey Route 210: On the hummer – Being on the bum but not down and out.
1948		McHenry & Myers Home Is the Sailor 19: I’ve been on the hummer for a week [...] I’ve been catching me a bowl of stew down at the Angel’s and flopping on the docks.