As the owner of
Performance Line Bearings I repair more than my fair share of ebike motors. We repair most makes of motors, including Brose.
What we have noticed is that each make of motor has its weak point, but it is usually only one weak point! Bosch, it's the lack of water tight seals (Now addressed on the Gen 3 motor). Yamaha, it's the lack of seals and a noisy drive gear. But with Brose there seems to be 5 main weak points!
1, Brose fitted a lovely water tight seal to cover the right-hand crank bearing, but water still enters the left-hand bearing.
2, Water regularly enters the needle roller bearing between the crankshaft and the sprocket carrier. (This is normally when you hear of people complaining that their pedals are stiff to turn backwards) Sadly, if this is not addressed quickly, it tends to destroy the bearing surface on the crankshaft.
3, There are two clutch bearings inside the motor called sprag bearings, one works when you pedal, one works when the motor assists. The bearings Brose use have plastic cages to keep the sprags in place. These plastic cages crack and the bearing starts to fail. (This normally manifests itself by a slipping sensation through the pedals and sometimes noise and notchy feeling through the pedals.
4, Drive belt tensioner failure. This is where the drive belt tensioner actually snaps, shortly followed by the belt stripping. (Felt as instant failure and loss of drive)
5, Drive belt stripping. (Normally felt as a soft bumping or jumping sensation through the pedals, shortly before all drive is lost).
Before you get too disheartened, please bear in mind that there are thousands and thousands of these motors out there, doing exactly what they should be doing, with no problems.
And Specialized have a great warranty attitude. And, when you're out of warranty we are here to help.