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Somewhat meaninless survey Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Mon, 9 Dec 2002 11:55:24 In Reply to: Brake Warning Lights, deeph8, Mon, 9 Dec 2002 10:28:15 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The ABS and Brake Fluid lights are BOTH on when the ABS system pressure is below 105 bar. The ABS pump runs until the pressure gets to 180 bar. When the car is shut off, the ABS pressure leaks down slowly, as the fluid moves from the pressure accumulator to the brake fluid reservoir.
How long the lights both stay on is a function of how low the pressure has dropped and how fast the pump can re-pressurize the system. The longer the car sits, the longer the fluid has had to drop down. But a lot of that depends on the car - a very minor leak rate difference in the porting valve can result in a big time difference at startup. Also, some folks have reported that the system pressurizes faster with fresh fluid, and this makes sense. Old fluid has water and air trapped in it, and the trapped air has to be compressed first before you can pressurize the accumulator.
Another big variable is the ABS pump speed. Yes, some pumps run faster than others, but they all run on volts. When you start your car, some voltage regulators sit at about 12.5 volts until the throttle is blipped, others jump right up to 13.5 or more. That 1 to 1.5 volts makes a BIG difference in pump speed. Also, outside temperature not only makes a difference in the alternator voltage (more voltage at lower temps), but it affects how fast the pump runs, and the ease of pumping (colder brake fluid is stiffer and harder to pump).
Lastly, older cars take longer to get pressure up - just like the rest of us.
Quite frankly, any time up to around 45 seconds for the lights to go out is fine. A really long time isn't good, but 25 seconds isn't inherently better than 30 seconds - so much depends on so many variables.
What counts is that the lights stay out when driving and braking. If you want a good test of the system, start the car and wait for not only the lights to go out, but for the ABS pump to stop running (buzz stops). Now, pump the brakes hard and fast. The lights should come on after about 12-15 pumps. That's normal. If the lights come on after only 3-5 pumps, you've got a problem with the ABS fluid accumulator.
You can have the lights go out very quickly and have an accumulator problem. So unless the lights take forever to go out, or come back on during normal braking, don't sweat it.
posted by 192.249....
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