Rob_B Posted December 5, 2012 Share Posted December 5, 2012 A friend of mine has a strange problem with his '97 300 TDI Discovery (automatic with ABS). On the road it is fine, but offroad he loses brake pressure. You need to press the pedal down twice to get pressure and brake. It feels like when you have been in water and mud and you some times need to press the pedal further down to brake the first time. But this one does it almost all the time. When you have pressure and wait a little (without driving the car), you need to press the pedal twice again. Any idea where to look for this problem? We have change to master brake cylinder for a new one and bled system a few times. And checked for wheel bearing play. The car doesn't lose any brake fluid. I can't understand why it only happens offroad and not when the car is used on the road. Thanks. Rob. Quote Link to comment Share on other sites More sharing options...
Tanuki Posted December 5, 2012 Share Posted December 5, 2012 Check the wheel bearings: if they are slack or worn then 'excessive' loads can cause the disc to be deflected, pushing the brake-pads/pistons further back into the caliper than normal. Then it can take a "pump" of the brakes to push the pistons back to the point where the pads actually contact the discs. Quote Link to comment Share on other sites More sharing options...
JimAttrill Posted December 5, 2012 Share Posted December 5, 2012 Damn! Tanuki beat me to it! That is without doubt the answer to your friend's problem It also happens on road cars if the bearings are loose. Luckily adjusting the wheel bearings is not difficult if you have the right box spanner for the hub nuts. Worth buying one if you don't have one. Best to take the hub to bits and renew the grease while you are at it. If greased well the bearings last for ever. Quote Link to comment Share on other sites More sharing options...
Rob_B Posted December 5, 2012 Author Share Posted December 5, 2012 That is what we thought at first too.Had that on an other car before. But the front wheel bearings where replaced already. And the rears have no excessive play either. These where re grease and adjusted not to long ago. Quote Link to comment Share on other sites More sharing options...
ianl1 Posted December 5, 2012 Share Posted December 5, 2012 My defender has started doing this, started during some off roading at the weekend and has continued at every brake use on the day and all this week back on the roads. Wouldnt a knock whilst offroading affect one side and cause uneven braking rather than an even lack off? Would this still be the likely cause if it is happening every time i brake, even if just roll forward 10 yards between succesfull double tap and next push? I was thinking leaking seal somewhere causing air? Quote Link to comment Share on other sites More sharing options...
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