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More info abt hydraulic systems than anyone should know Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Thu, 16 May 2002 09:18:11
In Reply to: ABS diaphragm?, Chris, Wed, 15 May 2002 15:31:55 Members do not see ads below this line. - Help Keep This Site Online - Signup |
First off, that sounds about right. It's just a lousy explaination.
Second, DON'T DRIVE THE CAR WITH THIS PROBLEM. See more below.
The ABS system stores pressure to run the ABS system AND for brake boost. If the pressure drops below a certain point, you get BOTH the ABS and Brake Fluid lights on.
The ABS system stores pressure in an 'accumulator' - a cylinder on top of the master cylinder, AKA 'da bomb'. It has a flexible diaphram (there is is!) inside - one side has nitrogen gas, the other side brake fluid. When the ABS pressurizes the accumulator, the diaphram moves, compressing the nitrogen gas. The pressure goes up, the lights go out, all is well. When you hit the brake, some pressure is let out for the brake boost - the gas expands slightly, forcing the fluid out. The energy, or 'throw', is stored in the pressurized gas - That provides the 'oomph' for the brake boost. Once the pressure has dropped far enough, the ABS pump runs, bringing the pressure up.
In your case, the diaphram has ruptured. Now the brake fluid fills the entire accumulator, and the gas escapes into the brake fluid, giving you a lousy pedal feel. The ABS pump runs and pressurizes the fluid, which turns out the ABS and Brake Fluid lights. But when you press the brake pedal, the pressure drops in the accumulator very quickly. Fluids don't compress well-that's why they're used for hydraulic system. So the lights come on.
The solution is to replace the accumulator - you can't fix just the diaphram. If the mechanic had said 'you need a new pressure accumulator', it would have made more sense.
Yes, these parts do go bad. Pressure accumulators live in lots of places, from car ABS systems to hot-water home furnaces to aircraft. And diaphrams break.
DO NOT KEEP DRIVING AROUND WITH THIS PROBLEM! It's much more than no ABS. The pressure provides Brake Boost. There is enough pressure in the system to provide a few brake applications, but the ABS pump is running like mad to keep up. If the ABS pump overheats, it will stop running, and overheat it enough, and you'll kill it - and an ABS pump is MUCH more expensive than an accumulator.
IF you lose the ABS pump, or you just get ahead of it keeping the pressure up, you'll lose brake boost. This will probably cause a crash. Without brake boost, pedal pressure increases dramatically. Braking distances will double or triple. Here's the scenario - you're coming up to a red light, and you expect your normal brake response. You hit the brake, and it feels stiff, and the car doesn't slow down. You take a few fractions of a second to recognize something is wrong, and now you have to lay into the brake pedal like you're doing a leg press at the gym. So you've lost about 20 or 30 yards to recognizing the problem and reacting, and then your braking distances are twice as long, even with the superman act on the brake pedal. Instead of stopping at the stop line, you sail through the intersection.
Of course, if there was a big truck stopped at the light, you won't make it to the intersection because you're now part of the trailer hitch. Interestingly, that's the GOOD scenario.
The intent here is to scare you. Most people assume the brakes will be there. If they aren't, they hit things.
The part should be available used. Also try some of the folks that advertise on this page. But I recommend having someone with experience install it. The system has to be de-pressurized carefully. Mis-installation can range from 'it doesn't work' to 'where do you want the flowers sent'. I recommend you have the brake fluid flushed - it's now filled with nitrogen gas, giving a lousy pedal feel.
Good luck!
posted by 140.157.4...
, Thu, 16 May 2002 09:18:11 <-- Viewing This Message
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