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Accumulator failures/testing Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Sun, 30 Apr 2006 20:44:40
In Reply to: ABS/Brake Fluid Light Flickers, Justin VanAbrahams  [Profile/Gallery]
, Sat, 29 Apr 2006 16:54:39
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The accumulator looks like a simple sphere, but it's much more.
Across the middle of the sphere is a flexible diaphram. The top side is filled with nitrogen gas; the bottom has brake fluid. When the ABS pump runs, it fills the bottom part with fluid; this presses up on the daphram and compresses the gas. This way the sphere fills (mostly) with brake fluid.
Brake fluid isn't compressible - that's why it does what it does. To store the 'power', the nitrogen is compressed - it's like filling a balloon, but in reverse - the balloon expands. As you use up ABS pressure, the gas gets to expand.
So, how does it fail? The gas leaks out of the sphere, usually due to a diaphram leak. The sphere now fills with fluid. You can pressurize it, sure. But you don't get any movement - the brake fluid won't compress, and that sphere isn't going to stretch like a ballon. You can pressurize the system, which makes the lights go out. but there is no pressure storage, so when you use the brakes, the ABS pressure drops very quickly, and the ABS and Brake Fluid lights come on. The ABS pump tries to keep up.
How do you test it? Easy. Start the car and let the ABS pressure come up - wait until after the lights go out, AND you hear the pump turn off. Now, pump the brake pedal hard and fast - like a bunch of firm stops, as quick as you can. Count the number of pumps before the lights come on.
A normal Accumulator will take 12 or more pumps to turn on. A weak accumulator is in the 5-12 pump range. Anything less than 5 pumps is a shot accumulator.
posted by 12.76.12...
, Sat, 29 Apr 2006 16:54:39, Sun, 30 Apr 2006 20:44:40 <-- Viewing This Message, Sat, 29 Apr 2006 17:23:38, Sun, 30 Apr 2006 01:06:11, Sun, 30 Apr 2006 18:30:54, Sun, 30 Apr 2006 20:00:27
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