Brake fluid leak at the booster - Chevy Impala Forums
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post #1 of (permalink) Old 12-15-2009, 06:47 AM Thread Starter
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Question Brake fluid leak at the booster

My 89 caprice was idling in the yard last evening. When I attempted to move it the brake pedal went to the floor and after multiple applications the red light came on. With a flashlight it appeared as the leak was near the master cylinder/ booster connection or under the booster. I could see fluid spraying. Does the booster contain any fluid or would the leak possibly be coming from the surface between the booster and master cylinder? No apperant leaks at the wheel cylinders.
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post #2 of (permalink) Old 12-20-2009, 07:03 AM
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Thumbs up Master cylinder

Your booster does not contain brake fluid unless the master cylinder has leaked into it, and in that case if the leak persists over a long period of time(you just keep adding fluid) then your booster will eventually fail due to the brake fluid attacking the rubber diaphram. Change your master cylinder. Begin by bleeding it on a bench(in a vise) use new clean brake fluid. Next install the master cylinder and bleed all four wheels. Do yourself a favor and flush the system. An easy way to do this is make a "one man bleeder" by placing a piece of vacuum hose inside a clear bottle with a little clean brake fluid inside. Make sure the vacuum hose is down far enough to be covered by fluid. Now go to the wheel farthest from the master cyl.,(usually passenger rear followed by drivers rear, then pass. front & so on) open the bleed screw and place the end of the vacuum hose over it. Now push your brake pedal slowly to the floor about ten times or until you see new fluid coming out of the hose. Close the bleed screw and check you fluid level in the resevoir. Repeat these steps for all four wheels-NEVER reuse brake fluid! The reason you flush the system (and this should be done every two years) is that brake fluid is very hydroscopic(loves water & absorbs moisture from the air), once brake fluid mixes with water ut becomes corrosive and starts eating away at your sealing parts & you develope a leak. Also once water(moisture) is in the system it lowers the boiling point of the fluid--when you hit the brakes at a high speed the fluid in the calipers and wheel cylinders will boil creating vapor which can be compressed. Once the vapor starts to compress you brake pedal sinks to the floor and you no longer have any brakes--a few quick pumps might save ya, but a little preventive maintenance goes a long way. Just like this reply has gone way to long
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post #3 of (permalink) Old 12-20-2009, 07:42 AM
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If you do not have a bench mounted vise another trick that you can do is mount the new master cylinder and do not attach the brake lines just yet. Pour in new fluid and have a helper push the brake pedal as you keep both of your thumbs over the ports that the brake lines attach to. Now you will get fluid every where but if you put some towls over your hands then you will contain most of it. Keep your thumbs tight over the ports and have your helper gently push the pedal several times. You will get air first then nothing but good clean fluid. Now attach the brake lines but snug but not tighten just yet. Loosen them about 1/2 turn and have your helper slowly push the pedal once you see clean fluid then tighten the lines. If it would help do one line at a time.

On 5 vehicles I have done this I have not had to bleed each wheel. But it could happen as the first poster said that you may need to bleed each wheel brake after the new master cylinder install.

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