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Thread: RT142/ST141 1 brake master options?

  1. #11
    Veteran Konakid's Avatar
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    Well the rear drums are quite a big bigger than stock and then there is the hydro master full of fluid as well so ill need a bigger master to combat that. I want a hard pedal!
    RT142 Estate.

    AJPS.

  2. #12
    Site Supporter Javal's Avatar
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    Chooch, the hydro is not a factor, apart from needing to put the prop valve before it so you don't restrict the hydro (which works fine) acting on the rear drums.
    The drum size isn't an issue either,it's that the wheel cylinders are larger and take more fluid volume to move before actually acting on the rear drums.
    At the moment, you're using 1/2 your pedal travel to take up the slack (NO this is NOT an shoe adjustment issue, for those playing at home) and actually build up system pressure, as the front and rear operate in tandem (tandem master cylinder).

    Restricting the rear line will mean the rears will do their work with slightly more progressive rear brake engagement due to the line restriction, but the rest of the system pressure will build up sooner, thus your pedal will be hard and because the pressure higher, sooner, your front brakes will work harder, sooner - which is the root cause of your issue.

    Just fit the adjustable bias valve. I can do the math on this if you really want. Save yourself the time, money and effort.
    You can have any brew you want... as long as it's a Datsun / Corolla / What is that?

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    Veteran maxhag's Avatar
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    The 1UZ car is running R33 front calipers, BA Falcon rotors, G series diff (TruTrac) with R33 rear Calipers and GZ20/MA70 rotors

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    Veteran Skylar's Avatar
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    Or option B. put disc brakes on the rear and ditch the drums. You duders have a pick-a-part/u-pull-it type wrecker? I'm dying to go dig up an ACR30 (from memory) and see what the rear brakes look like on those. Sucks we lost our pick-a-part 5+ hears ago. : [

  5. #15
    Veteran Konakid's Avatar
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    Yeah rear discs is a headfuck on the tarago f series, completely custom deal. Dont need them yet.

    Yes i know about the rear piston size causing the extra fluid, thats what i was alluding too when i said bigger rear drums, anyway...

    Im shopping for a willwood bias valve as we speak.
    RT142 Estate.

    AJPS.

  6. #16
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    Why is it a custom deal? just gotta find the right car and it's a bolt on deal (but I can't confirm since I haven't done it myself). and you get a drum handbrake too! Brakes are big though. Will need 15's.

    And it was a it was TCR10/20, not ACR30.

  7. #17
    Junior Member YRO 11A's Avatar
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    hey mate, jojo's housemate and bmxer54 on toymods, I am on here but seldom rarely.
    Are you sure that your current master cylinder is 15/16 as 13/16 is what i believe they run from factory
    on another note i have converted a yr22 f series to disc, it was a complete headfuck. Although, now that i have done it once i know exactly what to do again.
    If you need me to make all the bits you will need i can probably do that, my setup runs ma61 or mx73 backing plates, rotors and calipers with a custom caliper bracket welded onto the axle flange

    Cheers, Peter.

  8. #18
    Junior Member YRO 11A's Avatar
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    also if your shoes aren't adjusted up to the drums, that will cause excessive wheel cylinder travel, I'm going to look into master cylinder sizes for you tomorrow to try and get this issue resurrected for you, if you can't find an ra60/5 booster i reckon luke o'dea on fb will have something and he is in SA

  9. #19
    Veteran Konakid's Avatar
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    Hey mate thanks for the offer and i did see your write up on Toymods! At this stage im just going to try a bias valve on the rear line to remove some fluid from the rears and send it to the fronts.

    My only drama with this is that there will be less than fluid to the rears so it will be more prone to locking the fronts because they will engage earlier in the travel?

    Ill go this option first either way though before i hunt down an RA booster. Think i have a leak casuing air to get in teh rear atm too, the hydro handbrake now just lifts the whole way up a day or so after a bleed. arggh.
    RT142 Estate.

    AJPS.

  10. #20
    Site Supporter Javal's Avatar
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    Just to update my posts and give some tech insight to the thread -

    Myself and Konakid have spoken about this issue at lengths on the phone. Fitting an adjustable prop valve will be a bandaid fix for this issue, but an appropirate and cheap fix nonetheless. While it will (significantly) help with the braking performance issues this car has, in the end it all comes down to displacement. Brake setups (in a boosted application) should always be set up with the front piston surface area proportionate to the size of the master cylinder surface area. The rear caliper piston or wheel cylinder surface area can be equally matched or less than equivalent and adjusted for with a proportioning valve.

    Prop valves are ideally suited to situations where the rear braking setup has a surface area less than proportionate to that of the front / master combo (without one you would experience excessive rear brake lockup / mechanical bias) thus reducing the flow of the hydraulic medium (brake fluid) to the rear brakes giving slowed engagement.

    In this instance, the root issue with the car is that the rear wheel cylinder surface area is too large, the antithesis of what should be done when planning a brake upgrade unless the fronts and master are matched to the rear. Fitting a proportioning valve in this instance will still retain the long pedal travel (as the fluid must be displaced, no matter what restrictions are in place) but the braking performance will be increased as currently, the fronts brake do not build pressure to operate as the rear wheel cylinders are taking more fluid volume than they normally would to fill and start doing 'work'. Restricting the rear line will allow pressure to build in the master (and thus the unrestricted front circuit) sooner, thus letting the fronts work sooner and the rears come in to play at a more appropriate time. But as always, because the surface area of the slaves has been increased, the travel which the master goes through to displace an appropriate amount of fluid for the slaves will increase proportionately and his long pedal travel will remain the same.

    The 'real' solution to this issue is a front brake caliper upgrade to one with larger piston surface area, match the master cylinder to suit and restrict the rears (or don't, as required) with a proportioning valve. The circumstances surrounding this car (wheel choice i believe is the #1 issue) means that a front brake upgrade must be well thought out, thus a prop valve (which may be required regardless) is an excellent band aid solution while Konakid works out what path the to take to achieve his final solution to the brake system problem while compromising for his personal circumstances.
    Last edited by Javal; 2nd July 2014 at 12:53 AM.
    You can have any brew you want... as long as it's a Datsun / Corolla / What is that?

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