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Brake Fluid Loss

Brakes

Vehicle Information: Model: 911; Year: 1986; Body Type: Coupe; Engine (type, size, modifications): 3.4 L Turbo; Total Mileage: 250,000+;

Hi Chris,I have an issue with loosing brake fluid only at the track. My cars brakes have been modified to 78-80.5 930 front floating rotors with 944 front Turbo calipers and 81-89 rear rotors with 993 rear calipers. I have also upgraded the master cylinder to a Turbo and have installed a brake adjustment valve for the rears to control for rear wheel lock-up. Calipers were rebuilt last winter and a thorough examination of all lines, calipers and fittings indicate no leaks. As I have got more seat time at our home track at Mosport, I have obviously been faster, and, the faster I get the more fluid I loose to the point that the brake warning light comes on usually after cool-down after every second run thus requiring a top-up. The brakes are great and I never suffer from any fade or pedal mush. I run sports street pads which still have lots of wear after a track weekend. I use the Mercedes Benz brake fluid with a boiling point of 500F (Wet at least 356F). I note, however, that the overflow tube is wet and there are some traces of fluid around the outlet. My only thoughts at this stage are that maybe my standard 911 brake fluid reservoir is not is not big enough and/or the brake fluid that I am using has excessive heat expansion properties. I would appreciate your thoughts as to where else I should look, and, if you think that the reservoir may not be big enough and/or wrong fluid is used, I would appreciate your suggestion on alternatives.I always enjoy your Q& As.P.S. Sorry if this is the second email.

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