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  1. #1
    Join Date
    Feb 2006
    Location
    Somerset
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    1,093

    no brake pressure all of a sudden

    Hi
    Took the Cobra out today for a relatively long run around the Dorset coast on what was a lovely hot day. Everything was fine until about an hour into the journey when I had been stuck in a long line of caravans etc on a hilly coastal road. I put my foot on the brake pedal going down hill and the pedal nearly hit the floor!! I pumped it once and they worked OK. By the time we got to our destination which was another 20 minutes I was having to pump once or twice to get any pressure. We stopped and went for a walk and a think together with a drink and something to eat. When we got back to the car an hour later, the brakes seemed fine so we set off home, pledging to stop and call the RAC if the problem returned, which it didn't. Checked the brakes occasionally all the way home and they seemed fine. I haven't lost any fluid and I had it MOT 'd about three weeks ago so I know the pads and disks are good.
    The brake fluid needs changing as its over two years old, even though I haven't put any miles on it could that be part of the problem?

    I really have no idea so any thoughts would help

    Many thanks

    Martin

    GD427 Mk4. Chassis No J0258

    Ford 347ci Stroker - AFR 185 heads - Holley 670 - KB Pistons - Lunati "Voodoo" 272/280 Cam - 451 bhp/441 lbft.

  2. #2
    Join Date
    Feb 2007
    Location
    West Sussex
    Posts
    9,530
    Faulty seal in master or slave cylinder? Just a guess - can you see any leaks from either of these?
    Crendon Chassis No.49
    Huddart FE428 + toploader

    Not listed in the Shelby Register.

  3. #3
    Join Date
    Feb 2006
    Location
    Somerset
    Posts
    1,093
    No leaks that I can see anywhere?

    GD427 Mk4. Chassis No J0258

    Ford 347ci Stroker - AFR 185 heads - Holley 670 - KB Pistons - Lunati "Voodoo" 272/280 Cam - 451 bhp/441 lbft.

  4. #4
    Join Date
    Sep 2010
    Location
    Nova Scotia
    Posts
    986
    Stuck in that traffic may have caused engine heat to start the brake fluid boiling. Once the fluid cooled down, your brakes came back. Check to see if any of the brake lines are close to the exhaust. If so, you may have to insulate the line(s).
    John

    “A prudent person profits from personal experience, a wise one from the experience of others.”

  5. #5
    Join Date
    Jan 2009
    Location
    Dronten, the Netherlands
    Posts
    361
    Is any part of your brake system too close to an exhaust part, header/ downpipe? Too much heat and almost zero blow through under the hood could have resulted in some of the fluid reaching its boiling point which, as it's not the freshest, could have gone down due to water solved into it.
    Best not ignored, brake issues... .
    Good luck, Theo

  6. #6
    Join Date
    Feb 2006
    Location
    Somerset
    Posts
    1,093
    Putting new fluid in on Friday. Will check all of the above as well. She certainly gets very hot in traffic, but never had the issue before.
    Excuse my ignorance but what happens to brake fluid when it reaches to high a temperature?
    Thanks
    Martin

  7. #7
    Join Date
    May 2004
    Location
    Finchampstead, Berkshire, UK.
    Age
    55
    Posts
    3,836
    If you can’t find fluid anywhere (take the cover off behind the wheel to check the M/C) then boiling would be likely. Nice graph here showing the impact of old brake fluid on dropping the boiling point.

    https://epicbleedsolutions.com/blogs...of-brake-fluid

    Regards

    Jim
    GD Mk3 Jag based
    Supercharged LS1
    GD J1M

  8. #8
    Join Date
    Sep 2004
    Location
    Broughshane Ballymena Northern Ireland
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    Posts
    522
    Hi Martin, Brake fluid absorbs water over a period of time and normally this will not be a problem , but if it get too hot , the water boils and turns into steam creating a bubble in the brake line . It gives a similar effect to having air in the brakes . When it all cools down , the steam turns back into water and is reabsorbed into the brake fluid and the brakes will be fine again. This is why you need to change the brake fluid on a regular basis.
    As already stated , check that your brake lines are not too close to the exhaust .
    Jim

  9. #9
    Join Date
    Jan 2006
    Location
    Chelmsford Essex
    Posts
    1,668
    I would change the fluid first. To give you more temperature head room use DOT 5.1 higher boiling point than DOT 4.0 . Also look at shield you master cylinder and break pips near headers.. I would consider changing the master cylinder if it's old. Seals deteriorates over time and brakes are not to be messed with.

  10. #10
    Join Date
    May 2004
    Location
    Cowbridge, United Kingdom
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    10,347
    Agreed changing the brake fluid first is the way forward.
    I suspect in doing so you may discover that you can't bleed the system correctly, suggesting that you need to replace / repair the master cylinder.
    Also check the one way valve on the servo vacuum line if you have one.
    Kev Davies
    South Wales Area Rep. UKCC Membership Secretary
    DAX Mk4, 383 Chevy Stroker, Tremec. SOLD
    Contemporary CCX 3-4028, 445ci Big Block FORD FE,TKO 600, Old School IVA'd and SOLD
    Dax De Dion LS2 and T56 IVA'd June '17 SOLD
    1965 Ford Mustang 289 Convertible SOLD
    In build- Hawk 289 Sebring Awaiting IVA

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