Bench bleeding dual master cylinder procedure

[Jim S]

I have a new master cylinder to bench bleed.  It has a bleeder port on the small reservoir. How is that used? Will it only bleed that one, or will it bleed both the small and large resevoir. What is the recommended procedure?

[jccatwb]

I've never bench bled a master cylinder. Don't know why it is necessary or desirable .  Enlighten me.