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Thread: Brakes - Single or dual circuit?

  1. #1 Brakes - Single or dual circuit? 
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    The Marina roadster I have just started to rebuild has the original single circuit brakes.
    For safety I would like to change to dual circuit but so far I have failed to find a tandem master cylinder. They seem to be like hens teeth.
    So the questions are:
    Are there any downsides to dual circuit? I know that the dual circuit brakes on a Spifire have a dreadful reputation...
    Where might I find a master cylinder? I have tried all the usual places with no joy.
    As I understand it the bore of the non servo master cylinder is 0.7" (the servo one is 0.75"). Can anyone confirm that?
    At this stage I don't want to consider using a master cylinder from another vehicle, with the associated hassle of modification, as I see some others have done.
    I am also not currently considering a servo although that might change!
    Cheers Robin
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  2. #2 Re: Brakes - Single or dual circuit? 
    frequent forum contributor Club Member
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    Check out 'Car Builders Solutions' They have lots of info.
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  3. #3 Re: Brakes - Single or dual circuit? 
    frequent forum contributor Club Member jon_cox's Avatar
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    If it were me, I would go with a dual master cylinder setup using a servo delete solution like the one from compbrakes.
    https://www.compbrake.com/product/cu...inder-std-kit/

    CMB0336-PEDAL-BOX-BIAS-CUSTOM-UNIVERSAL-HYDRAULIC-STD-200x200.jpg

    You would need to upgrade your pedal box to one that was designed to take a servo if yours is a non-servo type.
    Last edited by jon_cox; 26-09-2020 at 07:02 AM.
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  4. #4 Re: Brakes - Single or dual circuit? 
    club member Club Member andyf's Avatar
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    I'm considering updating mine as well. I found that a TR6 servo and master cylinder will fit, or at least I found a reference with pictures of such an installation in the Morris Minor forum where the owner was upgrading to a Marina pedal box of all things. The page can be found here. I'm going down the route of building something like this to get bias adjustment as well as future proofing the installation
    Mk2 SWB Marina Roadster with a 2.0L Pinto built in 1986
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  5. #5 Re: Brakes - Single or dual circuit? 
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    I've just read that a master cylinder with servo from a Austin Allegro 73-75 bolts straight on and its dual circuit. Gleaned from Fast Marina site.
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  6. #6 Re: Brakes - Single or dual circuit? 
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    Two different beasts

    There are tandem master cylinders - so if one circuit fails you still have the other

    And dual master cylinders where you can have one on each "end" - and change the brake bias front/rear

    As all Marlins have radically different weight distribution to their donor cars IMHO you NEED the dual type so that you can move the brake balance to suit your car
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  7. #7 Re: Brakes - Single or dual circuit? 
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    My Roadster is over braked on the front and a suggestion was made to fit a pressure reducer in the font line to balance it. Car Builders IIRC.
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  8. #8 Re: Brakes - Single or dual circuit? 
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    Quote Originally Posted by HairyDave View Post
    My Roadster is over braked on the front and a suggestion was made to fit a pressure reducer in the font line to balance it. Car Builders IIRC.
    Hmm that's interesting. What is the configuration of your car?
    Cheers Robin
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  9. #9 Re: Brakes - Single or dual circuit? 
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    Quote Originally Posted by duncan View Post
    Two different beasts

    There are tandem master cylinders - so if one circuit fails you still have the other

    And dual master cylinders where you can have one on each "end" - and change the brake bias front/rear

    As all Marlins have radically different weight distribution to their donor cars IMHO you NEED the dual type so that you can move the brake balance to suit your car
    Interesting view. The problem is that cars with adjustable brake bias are not road legal in the UK I believe. They are certainly not allowed in the IVA.
    Cheers Robin
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  10. #10 Re: Brakes - Single or dual circuit? 
    frequent forum contributor Club Member chris_cussen's Avatar
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    Robin is correct. However if you use dual cylinders and find the best ballance then weld the adjustment then it will pass as it won't be adjustable....
    Cabrio, Omex 2.0l 150bhp Zetec blacktop, Omex ECU and wiring loom.
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