CONSPIRACY!
WHAT if your (Durango159)'s Convertibles are in need of new carbon brushes? I have an elder Metal base U4047 and it ran GREAT without the brush, but even with a fully free and moving original HOOVER brushroll, The cleaner slowed to barely a crawl!
I was advised to check the brushes, But have not got into that. My Eureka did the same thing about the brush slowing, I need to learn how to replace brushes! I've heard it's fairly simple, I'll have to order a commuter stone, But I'm likely to get my heart racing from the flying sparks! I've got Three projects backed up (The convertible, the Eureka, And a secret HOOVER surprise)!
Over Carbon Brushes. Anyhow, I'd recommend checking the carbon brushes, and ensure the motor can spin VERY freely, and resistance is not a good thing! you should see the RPM's on a freshly lubed cleaner (You've likely have, though)!