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Master Cylinders and rear disc on FJ40

Discussion in '40- & 55-Series Tech' started by Dunkane, Feb 21, 2007.

  1. Dunkane

    Dunkane

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    hi all !
    a question :

    with my new setup, rear disc brake instead of drum brake, i've got a new problem (if it is one), we change the DOT liquid, but no brake att all, the operation have been done 3x , no brake at all....is the disc brake setup could destroy an OEM master cylinder, due to the high pressure in caliper ?, or something else ?

    have i to mount a Master Cylinders of LC70 ?, or modify something in the setup ?

    best regards !
    Dunkane
     
  2. tlcruiser66

    tlcruiser66

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    Check to make sure you installed the calipers correctly (bleeders up). Make sure your bleeding the brakes rr, lr, lf, rf. Other than that, not sure without some more info.

    Kevin
     
  3. FJ40Jim

    FJ40Jim The Cruiser Whisperer

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    bleed order

    Bleed order is based on hydraulic distance from the MC.

    Correct bleed order on a 76-newer FJ40 is LR, RR, LF, LR.
     
  4. exmodlad

    exmodlad

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    you have to make sure you have the correct M/C for a disc brake rear as well as the correct proportioning valve
     
  5. Dunkane

    Dunkane

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    ok more details about the setup :

    - Master cylinder of BJ42 - 1984 , 18 months old
    - no proportionning valve

    the first time we made the mod of the rear brake , it was ok, good braking
    , after changing one brake aviation line by a hard brake line and refill all the circuit with the two method (normal by hand and also with the help of a special air pressurized tool in a tire shop)...nothing at all...brake in front, but nohing in rear....strange......i think there is two kind of Master cylinder, one for front disc and rear drum...and other for 4 disc, think my master cylinder is dead because of the high pressure.....or maybe i should looking for a voodoo :)

    if you have ideas..because i look in the FAQ, and noting...
     
  6. exmodlad

    exmodlad

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    M/C you have is disc/drum style

    you need to find a disc/disc style , valving is totally different for disc brakes in the rear....you must have a proportioning valve or you will have way to much juice going to back resulting in brake lockup

    i personally don't see to many benefits for disc's in the rear, as long as the drums and all the components are in good working condition...

    but thats up to you

    Best Regards

    Gord
     
  7. dgangle

    dgangle total rice SILVER Star

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    I suggest buying a gauge to measure the pressures at both front/rear ports of the MC and at each caliper. Stainless Steel Brakes sells one for about $50USD. Front disk pressures should be in the 1000-1600 psig range, rear disks 800-1200 psig and rear drums 600-800psig, in my experience.

    What's peculiar is that your arrangement is very common and that it worked properly before you replaced one of the hard lines, if I understand you correctly.

    Don't get hung up the whether you need a proportioning valve or have the right MC at this time. You have a different problem, at least for now.
     
  8. nuclearlemon

    nuclearlemon not an addict Moderator

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    you don't need a special master cylinder. you just need to remove the residual valves from the master cylinder (in where the lines screw in).
     
  9. Dunkane

    Dunkane

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    ok , tomorrow i try to remove the residual valves...i think to remove those for the rear..., i'm also waiting for a LC70 Master cylinder (KZJ70 master cylinder)
    i'll test it also, i 've a residual valve but nothing to mount it..i'll test...
    what is amazing, is the fact that the system was ok, before, during 1 week...and ine one time, nothing...i think the Master cylinder is Knoc out !..i'll verify !

    tanks, for your help, i'll give somes news !
     
  10. Dunkane

    Dunkane

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    ok , i changed for a HJ60 master cylinder, and all is good now.... ;), had no residual valve in the old AISIN bj42 master cylinder...for info
     
  11. dgangle

    dgangle total rice SILVER Star

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    I'm glad your problem is solved but this makes little sense. You said everything was fine until you replaced one of the hardlines, correct? This doesn't have anything ot do with the MC......./???????? Did you measure the pressures?
     
  12. Dunkane

    Dunkane

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    i have nothing to measure the pressure...somes news of my system, now i have the old MC of the HJ60, the brake is good, but not perfect, sure due to this MC, whic is a lilttle bit old.

    i receive a new MC of a 70 4 disc series (KZJ73), i mount it tomorrow and give you somes news...

    i'll put a proportionnal valve with a gauge to see what's happen on the rear..