The Sturmey-Archer AW freewheeling three-speed hub is extremely reliable. Unfortunately, Sturmey-Archer's record for three-speed coaster brake hubs is the very opposite.

The TCW series is particularly notorious for unreliability. They had so much trouble with the original TCW that the re-designed it, and came out with the TCW Mark II.

This was still a problem, so they came out with the TCW Mark III and later the TCW Mark IV.

All four of these hubs shared a fundamental design flaw:

They ran the brake through the gear train. This means that when you're in high gear, when you would be most likely to be going fast...the brake is at its weakest!

Even worse, if your shifter is mis-adjusted and you accidentally shift into the "neutral" position between 2nd and 3rd gear, the brake will not work at all!

This flaw was so dangerous that Consumer Reports magazine rated the TCW "unacceptable."

That finally got Sturmey-Archer to do yet another re-design, and to abandon the tainted "TCW" designation, so the new, improved model was designated "S3C."

This model ran the brake directly from the driver, so it was much safer than any of the TCWs. Unfortunately, the S3C is rather fragile, some internal parts are prone to breakage.

This was in turn replaced by the "AWC" model, which seems to be reasonably reliable.

Generally, if you have a TCW of any "Mark" version, I advise against riding it unless the bike has two good hand brakes.