A leak between Master Cylinder & Booster

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Feb 18, 2012
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Hello,

Quite confused though, I noticed Brake light is on at all times in instrument panel cluster. I checked brake reservoir is completely empty.And then I noticed there is a leak between Master Cylinder & Brake Booster. I tightened the 2 bolts holding the Master Cylinder to the Booster and drove it a mile and there is still leaking. The brakes seems normal though. May I ask which one is the culprit between the 2? BTW the vehicle is a 1984 Isuzu P'up truck
 
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Change the M/C asap because the brake fluid will get sucked in the booster and over time will damage it.
 
If the servo is good you can replace just the MC quite cheaply. Inspect all the hydraiulic system whilest you're in there because brake failure kills!
 
The seal that surrounds the rod that the booster presses on is likely going bad. I had this is my Odyssey and replaced it. Check RockAuto for a replacement. I think I spent $60.
 
Master cylinder piston seal is bad and / or the bore is worn. Replace the master cylinder.

The seal on the booster side has nothing to do with this. There is an intentional gap between the cylinder and the booster so that brake fluid from a leaky cylinder will run out the gap rather than getting inside the booster to damage it. The rubber parts inside the booster are not compatible with brake fluid. Some earlier designs did not have a gap, and then a leak in the master cylinder also meant the booster would fail.
 
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