'91 CB9
VERY hard to stop, very hard pedal & hissing sound while brakes are applied. I had this problem about a year ago and swapped a brake master & booster from my daughters '92 CB7 before she scrapped it. So, not 100% sure which one is at fault this time. I did read that hard pedal & hissing means it's the booster.
I did take the master & booster off my car earlier & correct me if I'm wrong but the booster is not suppose to have brake fluid in it....right? A lot poured out the vacuum port when I turned it over.
I'm heading to the junk yard first thing in the morning to look for boosters. Any tips on how to tell if it may be bad? Other than signs of brake fluid in or leaked on the outside of it?

THANKS in advance, this site is a savior.

 

Brake boosters should NOT have brake fluid. Brake fluid goes from master, into lines, into caliper. Period. Unless you have ABS, but it's only a line and the unit. NEVER brake booster.

Brake boosters are vacuum-based, there's a vacuum in there that as you push the brake, the vacuum makes it easier to push them forward as there's less resistance. Brake fluid in the booster means 1. you don't have a vacuum and 2. your master's leaking. Replace both.