BenjaminTDI Posted April 3, 2007 Report Share Posted April 3, 2007 Hi guys Had a card some time ago saying my A4 is due for a bi-annual brake fluid change. Just wondered if any of you knew much about why the brake fluid should be changed, I know it's a risk if moisture gets in and causes some problems, but I just wondered if any of you knew more about it than I did and would be kind enough to enlighten me as to whether it is worth doing or not? Comments would be greatly appreciated. Also, what are your experiences with Poole Audi as I am in Bournemouth for the next 6-8 weeks so I think that is the nearest stealers to where I am at the moment so will look towards them for taking care of the change if I decide to go ahead with it. Ben Quote Link to comment Share on other sites More sharing options...
paul_tdi Posted April 3, 2007 Report Share Posted April 3, 2007 hi Ben, Personally I would get Yeovil Audi to do it, they will come out and collect your car and did my latest service 170 quid less than what Poole quoted! They did a good job and were very helpful! I was going to use Poole as they were nearest to me but would not match the price, yeovil is further away but they collected and left a car FOC. Paul Quote Link to comment Share on other sites More sharing options...
kite Posted April 3, 2007 Report Share Posted April 3, 2007 Brake fluid is changed every 2 years because it absorbs moisture Quote Link to comment Share on other sites More sharing options...
MarskeBear Posted April 3, 2007 Report Share Posted April 3, 2007 ws qouted around £80 if done when i got pads chaged, told them to f-off. Local place done it for 30. Quote Link to comment Share on other sites More sharing options...
S4teve Posted April 3, 2007 Report Share Posted April 3, 2007 Ben, As the above says brake fluid absorbs moisture. When this happens two risks increase. 1) the chance of the brake fluid boiling (water has a lower boiling point) and if this happens air will also be introduced into the system (watch your kettle boil). Air can be compressed (unlike fluids) and therefore when you step on the middle peddle you get spongy brakes not good. This is extreme and is more likely to happen long after the two years and most likely in more demanding situations 2) Moisture in your brake system can introduce corrossion - not good either. Changing brake fluid is not a difficult job - the stealer did mine recently in no time at all. If you are due a service wait until then if not book it in - I think it's about £80 at a main dealer but not sure Quote Link to comment Share on other sites More sharing options...
UBM Posted April 3, 2007 Report Share Posted April 3, 2007 Actually, the brake fluid absorbs moisture which starts to degrade it. The inherent viscosity of the fluid falls over time, therefore, the fluid is thinner and it takes more pressure on the brake pedal to stop the car. Quote Link to comment Share on other sites More sharing options...
S4teve Posted April 3, 2007 Report Share Posted April 3, 2007 Mmmm, yes the fluid degrades but thin fluid dosent make it harder to apply pressure, only fluid that contains air will do this. Fluid of any viscosity cannot be compressed so will act on brake cylinders quite well. Hi performance fluids increase the boiling point and resist moisture and other air / fluid borne contaminents Of course not a suggestion but theorectically pure water can act as a brake fluid so long as you prevent boiling and corrossion. Quote Link to comment Share on other sites More sharing options...
UBM Posted April 4, 2007 Report Share Posted April 4, 2007 Be careful, I have a PhD in chemistry..... Seriously! Quote Link to comment Share on other sites More sharing options...
UBM Posted April 4, 2007 Report Share Posted April 4, 2007 What you mean is brake fluid is hygroscopic. It does not absorb gas, it absorbs water. This therefore lowers the viscosity of the brake fluid and also lowers the boiling point. In fact at about 2-3% water the boiling point of the brake fluid is lowered such that the water can evaporate into the gas state - which gives your "absorbed" gas phenomenon, and therefore affects braking. And by the way, liquids can be compressed, as can gases! Supercritical CO2..... And it is the anti-oxidants in the fluid that degrade over time too. So, the inherent reduction in viscosity is not the primary cause, it is the reduction in the boiling point of the fluid. The reduction of viscosity can be used as a test to check the status of the brake fluid. Quote Link to comment Share on other sites More sharing options...
S4teve Posted April 4, 2007 Report Share Posted April 4, 2007 [ QUOTE ] What you mean is brake fluid is hygroscopic. It does not absorb gas, it absorbs water. This therefore lowers the viscosity of the brake fluid and also lowers the boiling point. In fact at about 2-3% water the boiling point of the brake fluid is lowered such that the water can evaporate into the gas state - which gives your "absorbed" gas phenomenon, and therefore affects braking. And by the way, liquids can be compressed, as can gases! Supercritical CO2..... And it is the anti-oxidants in the fluid that degrade over time too. So, the inherent reduction in viscosity is not the primary cause, it is the reduction in the boiling point of the fluid. The reduction of viscosity can be used as a test to check the status of the brake fluid. [/ QUOTE ] OK so you explained it better than me But basically - however the air gets in there (after the degrading and then boiling etc etc) it is the air that causes spongy brakes - right P.S I'm not trying to out do anybody here Quote Link to comment Share on other sites More sharing options...
jackrory Posted April 5, 2007 Report Share Posted April 5, 2007 had mine done at an independant whilst having my last service..cost on bill- brake fluid change...£4.80. but my car is 4 years old and out of warranty so i can understand going to a dealer if its a newer car. Quote Link to comment Share on other sites More sharing options...
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