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Dual brakes sticking on.

Discussion in 'Brakes' started by Barten, Jan 16, 2018.

  1. Tom W

    Tom W Member

    This looks the same as the setup on a Jaguar E-type 4.2. Sticking brakes is a known problem with them, if you search the web for “Sticking Jaguar reaction valve” there’s lots of info available. As far as the Jaguar system is concerned, there’s a couple of different sources of the problem, but initial symptoms are similar.

    The little push rod in the end of the master cylinder can stick and fail to retract fully. This causes the reaction valve to open and servo to operate, even when the pedal isn’t pressed. The reaction valve and the pushrod are only held closed by a small spring under the reaction valve cover. This can corrode slightly and go weak over time. Dirt in the reaction valve could prevent it sealing properly, or a split diaphragm could also cause problems.

    The other area to give problems is the servo. On the Jags, at least, this has 2 independent hydraulic systems in it. These are separated by a shuttle piston that’s free to move along the servo bore to balance the pressure in the two systems. Pressure in the primary system is transferred to the secondary system through this shuttle. Corrosion and debris in the servo bore can cause this shuttle to stick, retaining some pressure in one or other of the systems.

    A final area to check is replacing all the vacuum hoses on the system. These can go soft and collapse, holding the vacuum on when it should be released. Be sure to use proper vacuum hose, heater hose is no good.
  2. Barten

    Barten Member

    Thanks for your input Tom and Clive. I will certainly check out the thing you mentioned. Don't think I will have time to do it before my next work period though. But in about 3 weeks I will dive into it again!
    Regards, Barten
  3. Barten

    Barten Member

    It has been a long time and I have changed out my master cylinder - still the brakes were stuck on( only on front wheels). Yesterday I decided to take off the servo with the slave cylinder. I thought maybe there was something wrong with the way I had reassembled it. Looking at the drawing in the WM it seemed like I had locked the rod inside the servo assy incorrectly. That had prevented the piston from releasing properly when I relaxed the brake pedal. I assembled it like the book said, installed it and voila-- brakes were not sticking anymore! Result. Now I just have to bleed the dual system properly. I felt there was a tendency for the brake pedal to be a bit sticky, ie not coming back out after I pressed it. Now I can check some of the other issues like the wipers not working correctly, the tacho not working and the speedometer must be recalibrated ( 5 speed gearbox). And not to forget fitting all internal stuff still missing plus the outer badges and chrome.
    Regards, Barten
  4. mrtask

    mrtask Well-Known Member

    Sounds like you've had a real result, Barten. Great stuff. Needless to say you've got a list of other things to rectify, isn't that always the way with these fine old cars!? Keep working your way down your list, and if you've any recent photos of your pride and joy, let's see 'em! If you haven't, well it is time to take some, eh!?

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