No, it isn't safe ! You never know when it might just go all the way out and make it very difficult to stop your truck ! Get that taken care of right away. After all, it's there for a reason, isn't it ? From your mechanic.com
What does a power brake booster do?
- A brake booster makes it easier to push the brake pedal. It is a vacuum assist system. If the car did not have a brake booster, it would be very hard to push the brake pedal and stop the car. The brake booster is located underneath the hood in the engine compartment, behind thebrake master cylinder.