Mrbus Posted April 3, 2010 Share Posted April 3, 2010 For some reason my brake pedal "hisses" & stops when i press it. Im guessing it is something to do with pressure. I think my brakes work fine & im sure it didnt make that noise before. Any advice on if it should be like that, or is something wrong? Its a manta B GTE/E. Might also sell but not sure how much its worth? 1987 GTE/E hatch 107k MOT sep10 Quote Link to comment Share on other sites More sharing options...
upk Posted April 3, 2010 Share Posted April 3, 2010 from what you say it could be the servo thats failed and what you can here is the vaccumn suction pull on the servo!! Quote Link to comment Share on other sites More sharing options...
philip warren Posted April 3, 2010 Share Posted April 3, 2010 yeah sounds like the diaphragm in the servo has split. Quote Link to comment Share on other sites More sharing options...
mantadoc Posted April 3, 2010 Share Posted April 3, 2010 Air is supposed to enter the servo via the area around the brake pedal as it has a foam filter around the pedal rod If air couldn't get into the servo it would not work, think about it the pipe into the inlet manifold should have a one way valve in so no air flows back in up the vacuum pipe and into the manifold and these only work by allowing air in to press on one side of the diaphragm and move towards the low pressure engine side. I've had some you can here and some you can't. Quote Link to comment Share on other sites More sharing options...
Retro Power Posted April 4, 2010 Share Posted April 4, 2010 vacuum is always applied to both sides of the servo under normal driving conditions. When you brake air is admitted to the "pedal side" through the foam filter so that the vacuum pulls the brakes on. If its hissing its the air admittance valve leaking slightly Quote Link to comment Share on other sites More sharing options...
mantadoc Posted April 5, 2010 Share Posted April 5, 2010 For some reason my brake pedal "hisses" & stops when i press it. So hissing when not pressing the pedal is bad.......... hissing when using it (letting air in) expected Quote Link to comment Share on other sites More sharing options...
Retro Power Posted April 5, 2010 Share Posted April 5, 2010 Yep, only when you press the pedal you open the valve a lot so it won't really hiss, it just lets air "waft in" so to speak Quote Link to comment Share on other sites More sharing options...
mantadoc Posted April 5, 2010 Share Posted April 5, 2010 That's what I thought, cool Quote Link to comment Share on other sites More sharing options...
Mrbus Posted April 5, 2010 Author Share Posted April 5, 2010 So what exactly is the part i need to change? The brakes seem fine when i keep my foot on the pedal as it does not gradually sink to the floor, so im guessing they are fine. I just get the hissing noise when the pedal is not pressed! Quote Link to comment Share on other sites More sharing options...
Retro Power Posted April 5, 2010 Share Posted April 5, 2010 You don't "need" to change anything. Your brakes will still work normally, the master cylinder return spring will be enough to prevent the leak from actually pulling the brakes on. If you wanted to get rid of the hiss then you'd be best to change the whole servo unit as I've no idea how to get the valve out, never done it! As a quick check, its worth making sure that the brake light switch isn 't stopping the pedal from fully returning, as this could cause it to leave the valve very slightly open and cause the hiss. Nothing to panic about in any case though Quote Link to comment Share on other sites More sharing options...
IanMc Posted April 6, 2010 Share Posted April 6, 2010 Any use? Ebay item Quote Link to comment Share on other sites More sharing options...
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