the old system of gentleman's agreements did not prevent the abuse of the fillibuster.
whenever i hear that term "gentleman's agreement" i remember that a gentleman's agreement between the airplane manufacturer Macdonald-douglas and the FAA where the company promised to fix a flaw in it's new D.C-10 aircraft where the cargo door of the plane would fail to lock, and led to explosive decompression. after a near miss, Macdonald-douglas promised to fix the cargo doors on the d.c 10, but begged the FAA not to issue a order to ground the d.c 10 and go through a redesign of the cargo door.
that gentleman's agreement did not lead to the fixing of the flaw, and the result was the crash of turkish airlines flight 981, when all 346 people on board perished when the cargo door unlocked and blew away from the aircraft, causing explosive decompression which destroyed the planes hydraulic systems and rendered the plane uncontrollable.
if you need to get a better understanding of the accident, check the link
Turkish Airlines Flight 981 - Wikipedia, the free encyclopedia