Vacuum Hose

• If the vacuum hose coming from the manifold and entering the side of the unit is corroded or cracked, the Cherokee will not have full braking power. If that is the case, do not attempt to repair the hose with tape or silicone. It is much safer to replace it altogether. Also, sometimes the connection itself could be loose or worn, and may need a new gasket; you can find this at any parts store. Check the clamps on both ends, too, to ensure a proper seal on both the master cylinder and the manifold.
  
  

Fluid Seal

• The master cylinder contains a tray that holds the brake fluid. If the rubber seal on the lid of the tray has torn or is squished in there, brake fluid might be allowed to squirt out of the cylinder, greatly reducing pedal pressure and braking ability. Remove the bolt and inspect the gasket and fluid level. If the fluid is not up to the full mark, braking can also be affected, especially when the vehicle is at an angle. If the tray itself appears to be leaking, replace it with a new or remanufactured unit.
  
  

Plunger

• Inside the master cylinder, there is a plunger that is activated when you depress the brake pedal. When compressed, it adds pressure to the fluid in the lines, pushing outward on the brakes. If the plunger has a bad seal, it will allow brake fluid past it, and the result will be a weak-feeling brake pedal and lack of stopping power. If the plunger seal is bad, replace the entire unit unless you are skilled enough to rebuild it.