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  1. #1
    Join Date
    Feb 2005
    Location
    Crowthorne Berkshire
    Posts
    126

    Sumo Mk3 New Cosworth spec Rear Calipers - Brake bias ?

    Hi all,

    I just had an unfortunate incident after a recent replacement of my old rear brake calipers , after the handbrake adjuster had nearly given up both sides, where the car spun out of control nearly taking me out in the process!!

    I'm still waiting for the car to be returned to me, but thinking if possibly because the rear brakes are now far more efficient , they may have locked up before the fronts (Hi-spec twin pots).

    I believe the original scorpio/sierra fitment was ABS all round, but also a proportioning valve between font and back mounted at a critical angle to stop any chance of rear lockup?

    In the 35k miles before the replacement of the rears , i have never had any indication of the rears behaving erratically , but bearing in mind the rears calipers would have already been 15 yrs old, so likely not that efficient?

    Although the new calipers were cosworth spec, they appear to be exactly the same specifications of the standard scorpio ones , and there was a lot of different part numbers applicable to both.?


    Once I get the car back I'll thoroughly test it out, but even an MOT wont pick up on differential brake bias, so interested to get opinions here?



    Thanks...

  2. #2
    Join Date
    Nov 2012
    Location
    South of Winchester
    Posts
    165
    Brake bias does sound a likely culprit - you could test it in the same way they do in the IVA - drive at about 20mph and jam on the brakes very hard - have a knowledgeable person watch and see if the rears lock up before the fronts - brake bias valves are easy to fit and adjustable ones are readily available/cheap. Not sure who would have the same sort of testing equipment as the IVA station but maybe its also worth a visit/call to your local one??????

  3. #3
    Join Date
    Feb 2005
    Location
    Crowthorne Berkshire
    Posts
    126
    Thanks Phil,

    I was going for a more graceful approach , by applying gradual brake pedal, and see if the front wheels rotate freely before the rears, but either way seems good.

    Of course I have not ruled out the rear calipers are a diiferent spec, as after market versions sold by rallydesign.

    I'll update the thread when I know more👍

  4. #4
    Join Date
    Mar 2005
    Location
    BERKSHIRE
    Posts
    620
    did you do much damage to the cobra ?

  5. #5
    Join Date
    Dec 2008
    Location
    Newcastle upon Tyne
    Posts
    1,848
    Hi ? (-sorry don't know your name)

    Hope the car was not too badly damaged and you are back on the road soon, sounds like a scary experience!

    Are you using the standard Sumo brake pedals & servo from a Sierra and did you make any changes to the master cylinder when you fitted the HiSpec front calipers?

    I am interested as I am currently changing the brakes in my Mk3 Sumo after removing the brake servo to get the new engine (Lexus 1UZ-FE) further back in the engine bay. Planning to upgrade the front brakes to HiSpec Billet 4 calipers with a 300mm vented rotor and need to size the front master cylinder.

    I believe, from memories of previous test (not always reliable!), that they test the front and rear brakes separately so should be able to give some indication of relative performance.

    Good luck with it!


    Regards,
    Ian
    Pilgrim Sumo Mk3; IVA Apr. 2014; RV8 3.9 EFi ; Cosworth T5; Granada Donor
    Phase Two underway - Conversion to Japanese

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