Subsequently, he shared the reign in the reunited duchy of Saxe-Lauenburg with John and his brother Eric V. However, most of Saxe-Bergedorf-Mölln had been alienated, such as the Herrschaft of Mölln (sold to Lübeck in 1359 under a repurchase agreement) and the Herrschaft of Bergedorf, the Vierlande, half the Saxon Wood and Geesthacht, all of which Eric III had pawned to the city of Lübeck in 1370.
On a visit there under safe conduct granted by the Hamburg's senate (the city government), his creditor Heyne Brandes [de] (later in modern standard High German also: Hein Brand[t]) took the defaulting duke to task and dunned him in a way the duke considered insulting.
[4] This caused a civic uproar of Hamburgers, electing from each of the then four parishes 12 representatives, the Council of the Forty-Eighters (die Achtundvierziger), who on Saint Lawrence Day (10 August) stipulated with the senate the Recess of 1410 (considered Hamburg's oldest constitutional act), denying the senate's privilege to arrest without a prior judicial hearing.
[5] In 1411 John IV and his brother Eric V and their father Eric IV pawned their share in the Vogtei over the Bailiwick of Bederkesa and in the Bederkesa Castle [de] to the Senate of Bremen including all "they have in the jurisdictions in the Frisian Land of Wursten and in Lehe [de], which belongs to the afore-mentioned castle and Vogtei".
[6] Their share in jurisdiction, Vogtei and castle had been acquired from the plague-stricken Knights of Bederkesa,[6] who had dropped into decline after 1349/1350.