Errr, ehe, ahem... yeah, right. Like the Sturmey Archer 5 speed IG hub? With a 90 mm drum? The days of the tandem drum drag brake are gone. The problem the OP had was that the brakes were not sized correctly for the terrain they ride in.

My initial choice of Hope E4 brakes was a mistake on my part. They were fine on relatively flat roads we ride on here in North Dakota and Minnesota. They were not up to steep hills and high speeds. The Hope V4 brakes with the Hope vented rotor have never had any issues. Even as a drag brake on a touring tandem that can be carrying as much as a 500 pound load maintaining 30 MPH on long steep hills.

By the way, a Hope V4 brake set with a vented rotor runs about $300.00, which is less than you will pay for an Arai drum work alike today, and it is superior to the Arai in every possible way; lighter, stronger, fade resistance, absolute stopping power. Boiling fluid? Use Castrol SRF brake fluid. Yeah, it is expensive. Very high boiling point. Cheaper than surgery.