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And the bad news is... Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Tue, 4 Jan 2005 06:17:56
In Reply to: braking problem c900, bobby, Mon, 3 Jan 2005 21:27:05 Members do not see ads below this line. - Help Keep This Site Online - Signup |
That's the ABS pump. That pump provides pressure for both the ABS system and the brake boost. That pressure is stored in the accumulator, that black sphere sitting on top of the master cylinder.
I assume that you're also seeing the Brake Fluid and ABS lights on. Those lights will BOTH come on when your ABS pressure is too low. Yes, there are pressure switches-
If the ABS pressure is less than 140 Bar (atmospheres), the ABS pump will turn on. It'll keep running until the pressure (in the accumulator) reaches 180 bar. Normally, the pressure drops down slowly, some due to leakage past a valve, and from using the brakes. Pressure drops down to 140, the pump starts back up. If the pressure is less than 100 bar, you get both the ABS and Brake Fluid lights. At 100 bar in the accumulator, there is about 5 full stops with brake boost left.
But if the pump doesn't run, you get no pressure.
If you aren't getting the Brake Fluid and ABS lights, then I'd suspect problems with the pressure switches. Not only would they not light the lights, they wouldn't tell the ABS pump to run.
However, if you do have the lights, it could still be the pressure switches, but I would suspect either the ABS pump relay, or the ABS pump itself. Especially true since a tap gets things going. Near the master cylinder you'll find the ABS Main Relay and the ABS Pump Relay. Make sure they're well seated. If tapping the relay gets things running, I'd pull the relay and clean the contacts - open it up, and clean the contact points with some fine sandpaper - lightly! Take off the carbon, but don't take off the thin metallic coating.
If it isn't the relays, then it can be a sticky ABS pump. I've come to that last because it's a very expensive part. Saab parts aren't cheap, but ABS parts are very, very expensive. A new pump can easily cost $1000. If it turns out to be the ABS pump, think about a used one. However, do LOTS of troubleshooting first.
posted by 192.249....
, Tue, 4 Jan 2005 06:17:56 <-- Viewing This Message, Tue, 4 Jan 2005 12:17:03
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