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Old 11-01-2008, 10:26 PM
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If the ABS no worky the rears can be very easy to lock up, so drive carefully.
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Old 11-02-2008, 11:54 AM
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It rained heavily and now it all seems to be working again lol...

Thats got to indicate its an electrical fault at a sensor..I think....

I am awaiting some new belly pans and converter from Roger (928Rus) , also will be fitting a wideband/gauge, so will strip all the wheels and sensors down while I have it in the air....

All the best Brett
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Old 11-02-2008, 12:15 PM
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Originally Posted by 123quattro View Post
On a car with ABS, the best way to disable it is to unplug the wheel speed sensors. That will immediately fault the system (at least a newer system). For the 928 I'm not so sure since it's modulations is 3 generations old, but on newer stuff with two sensors pulled you still get electronic brake force distribution, EBD. That drops pressure in the rear circuit. If you just pull the fuse on an ABS car you will have too much rear pressure. In effect it's the same as totally removing the prop valve on an older car. The hydraulic unit runs higher brake pressure than normal at light applies, and then limits rear pressure builds as total circuit pressure goes up. Pulling the fuse removes that functionality.
I don't believe this functionality exists on a 928 system - remember it was one of the earliest production ABS systems. As far as I am aware When it faults for anything - it shutsdown everything.

It does have various failsafes - but the biggest concern seems to hane been that it would operate when it should not and reduce brake circuit pressure when that would be dangerous... obviously a major liability issue for the manufacturer (Bosch) and a black mark against ABS in general.

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Old 11-02-2008, 12:31 PM
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Originally Posted by Jfrahm View Post
If the ABS no worky the rears can be very easy to lock up, so drive carefully.
When my ABS failed the fronts locked easily to the point I smoked the PS2s down to the cords with the OEM bias valve.

With the ABS repaired, the 33 bar bias, new rear rotors and pads the car now brakes very hard with little nose dive. PBR ceramic pads all round.
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