mac9k5 Posted November 15, 2009 Share Posted November 15, 2009 Hello, I am not sure what is going on. When i press the brake pedal in my 280z slowly the pedel will just go to the floor with no braking power or fight. but when i stomp on the pedal the thing will stop on a dime or lock the wheels IE works well. I have bled the brakes countless times trying to make them better and they seem to get worse over time untill i bleed them again. any advice or info. Thanks. Quote Link to comment Share on other sites More sharing options...
kiwi303 Posted November 15, 2009 Share Posted November 15, 2009 I think that's the sign of a bad seal in the MC, as you press slowly there's time for the fluid to ooze around and through the seal on the shaft. but when you stomp on it theres no time for it all to get out. as to bleeding, fluid getting out also would suggest air can get in through the same place, hence the need to bleed reguarly. If you have a parts car sitting around, swap the MCs over and see what happens? Quote Link to comment Share on other sites More sharing options...
DAW Posted November 15, 2009 Share Posted November 15, 2009 Are you losing fluid? DAW Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 15, 2009 Share Posted November 15, 2009 That is the classic test for a master brake cylinder. Yours failed. You might be losing fluid into the master, you might also be transferring it from the front reservoir to the rear. Regardless, your master needs to be changed. Quote Link to comment Share on other sites More sharing options...
DAW Posted November 15, 2009 Share Posted November 15, 2009 Almost any leak in the system could give that sign (push fast is firmer than push slowly). However, if you are losing large amounts of fluid it could also be a bad wheel cylinder or caliper, or a loose bleeder screw. The pathognomonic test is to push quickly to get a firm pedal, then ease up a bit on the pedal pressure - - if the pedal now drops when you eased up; then your master cylinder is defective (and you may find some fluid in the dust seal on the master; or soaked into the paint and your carpeting under it). DAW Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 15, 2009 Share Posted November 15, 2009 Almost any leak in the system could give that sign (push fast is firmer than push slowly). However, if you are losing large amounts of fluid it could also be a bad wheel cylinder or caliper, or a loose bleeder screw. The pathognomonic test is to push quickly to get a firm pedal, then ease up a bit on the pedal pressure - - if the pedal now drops when you eased up; then your master cylinder is defective (and you may find some fluid in the dust seal on the master; or soaked into the paint and your carpeting under it).DAW I suppose you're right, I just assumed that there weren't any other obvious leaks as it sounds like he's been over the system a bunch of times. Quote Link to comment Share on other sites More sharing options...
DAW Posted November 15, 2009 Share Posted November 15, 2009 the same basic rule applies. I recently had a soft pedal on my 510 and it turned out to be a bad rear wheel cylinder and NOT the master cylinder (of course I discovered this after I had already bought online the master cylinder rebuild kit). DAW Quote Link to comment Share on other sites More sharing options...
turboboost Posted November 16, 2009 Share Posted November 16, 2009 I had this problem on my off-road truck. I replaced the master cylinder and all problems went away. Quote Link to comment Share on other sites More sharing options...
psdenno Posted November 16, 2009 Share Posted November 16, 2009 My 914-6 is currently in the shop getting a new M/C after presenting me with the same symptoms. Unfortunately, the Porsche M/C is quite a bit more labor intensive to replace than the one on the Z. Dennis Quote Link to comment Share on other sites More sharing options...
Z lion 71 Posted November 21, 2009 Share Posted November 21, 2009 i would replace out the mastercylinder first.more than likely your problem.then hit the wheel cylinders next.make sure you bleed the system well.get all the air bubbles out. Quote Link to comment Share on other sites More sharing options...
shika805 Posted November 22, 2009 Share Posted November 22, 2009 seal in the MC... like stated. happened to me a few times with cars Quote Link to comment Share on other sites More sharing options...
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