Serious safety issue! -Master cylinder mods

Discussion in '40- & 55-Series Tech' started by lostmarbles, Oct 28, 2007.

  1. lostmarbles

    lostmarbles SILVER Star

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    UPDATE: ----AT POST 56 OF THIS THREAD I'VE BECOME LESS SURE THAT THE REMOVAL OF THESE "VALVE THINGIES" WILL BE HARMFUL AND NEED STILL MORE HELP TO BE ABLE TO UNDERSTAND WHAT EXACTLY THEY DO. - Sorry if the title of this thread has raised alarm unnecessarily (Still too early for me to tell) Lostmarbles -1 November 07

    It is becoming apparent (to me at least) that there may be a serious safety issue concerning the modifications some people are making to their brake mastercylinders.

    I am talking about the removal of so-called "residual valves".

    Have a look at the posts in my thread "What are these" to see what I'm talking about.

    Here's the link (if I can follow Pin_Head's advice properly): http://forum.ih8mud.com/showthread.php?t=185090

    It is possible there are other types (to mine) of "residual valves" fitted ex-factory to our 40 series cruisers - but I can say for certain that my type are there to serve an important safety function. (And that function is just as important for a vehicle fitted with disc brakes as it is for one fitted with all-drums.)

    Yet it appears to me as though some of these same-type valves are being discarded during vehicle modification work.

    Any comments?
    Last edited: Oct 31, 2007
  2. Pin_Head

    Pin_Head

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    What safety issue?

    I only know that people remove them when they convert to disc brakes, because disk brake masters don't have them. They don't keep the pistons from returning completely as some in the other thread have claimed.

    I read the other thread and you are right that these particular valves are just one way flow regulators that bias flow in the cylinder direction. This will slow the rate that the piston returns. Unlike other masters, these don't maintain any residual pressure.
    Last edited: Oct 28, 2007
  3. bandy rooster

    bandy rooster

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    your kind of unclear on what your saying or asking ... or maybe i don't understand

    as far as i know most disc brake vehicles still use residual valves but there usually 2 lb not the 10 lb versions on most drum brake vehicles...

    what do you mean by safety function?
  4. lostmarbles

    lostmarbles SILVER Star

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    Thanks Pin-Head. This is getting into quite a good discussion!!
    If disc-mastercylinders don't have them, then they must surely have something else that performs the same job.

    Not true for the "thingies" that I removed from my ex-factory mastercylinder. The photos prove that they don't serve that task at all,
  5. lostmarbles

    lostmarbles SILVER Star

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    Sorry - You'll need to read all the dribble I placed in the "what are these" post.

    If I knew how to make a link I would
    :cheers:
  6. Pin_Head

    Pin_Head

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    I edited my post to reflect my reading of your other thread that I hadn't seen yet. Other vehicles are different and they are actually used to retain residual pressure, but from the pictures you posted this is not true for the Toyota ones.

    I doubt that they are a "feature" to allow you to run misadjusted brakes by double pumping the brakes, because this is a very bad idea compared to having them adjusted correctly. I'm not sure what the purpose is, but obviously the fluid returns more slowly to the master.

    I honestly don't thing that you need to remove them for a disk brake conversion either because they don't retain pressure.

    To add a basic link, all you need to do is copy the URL from your browser and past it into the message.
  7. lostmarbles

    lostmarbles SILVER Star

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    I agree fully Pin_Head. What really worries me is that some people may be discarding the "Toyota type" thinking their purpose is just to leave "permanent residual pressure" in the brake lines - when this is a job they don't even attempt to do.

    I doubt that too. I didn't mention "badly adjusted brakes" in connection with what they are there for. I believe they are there to give you "emergency braking" (through pumping-the-brakes) when air is trapped in the fluid system. And a typical way air enters is by a leaking seal draining fluid out and the owner then retopping the reservoir after air has already entered too far.

    Without these "Toyota valves" you haven't a hope in hell of getting a "hard-pedal" by pumping the brakes. So this must prove they are fitted for safety reasons.

    Good. Me too. And thanks for the info on making a "Link". I'll try that.
  8. gladly

    gladly User title SILVER Star

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    if I were looking for a serious safety issue, I'd look first at your master cylinder, as shown in the other thread:
    [​IMG]

    there is a reason that master cylinders generally have two reservoirs. If something happens in the front or rear circuits (eg. a ruptured brakeline) if you have the stock setup (two reservoirs) you will be able to maintain braking pressure at the other end of the truck. however on your master cylinder, modified from stock as it is, a leak at one end would be able to puke out all the fluid for the entire braking system of your vehicle!!

    edit, in case you are thinking that the fluid would all be lost regardless, there are two seperate pistons in the M/C and one dry reservoir will not cause the other circuit to lose fluid or function
    Last edited: Oct 29, 2007
  9. Pin_Head

    Pin_Head

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    I don't think so. Air bubbles make the pedal feel "spongy" or soft, but it doesn't lead to a hard pedal by pumping it. The pedal is firm at the end of the stroke with air bubbles; it just takes a little more to compress the air.
  10. lostmarbles

    lostmarbles SILVER Star

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    Now I thought you were going to point to the cut vacuum line on the booster Gladly (but perhaps it never showed up well in the photo)!!!!!!

    The reservoir is easily explained. While it may look like a single reservoir, it actually has two separate internal compartments for the very reason you mention. And I'm afraid it is completely "stock".
  11. lostmarbles

    lostmarbles SILVER Star

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    Maybe "hard" was a bad word choice Pin_Head.

    Try this:

    In an unmolested vehicle, if there is sufficient air contamination, it may take several rapid pumps-of-the-pedal before you'll achieve a "pedal pressure" that will produce any braking force at your wheels to enable you to stop. (Obviously if the contamination is too severe you may NEVER get pedal pressure.)

    However if you were to be driving a vehicle with a mastercylinder like mine where the "toyota valves" have been removed with the same level of air contamination, you would never ever ever ever (enough evers?) achieve the "pedal pressure" and "braking force" result you would be desperately striving to get.

    In my mind's eye I can see you're right foot pumping up and down at 50 cycles per second with your eyes bulging as you speed towards everlasting peace!

    OK - I concede I'm ignoring the safety-effect of having the front and rear brake circuits separated
    Last edited: Oct 29, 2007

  12. gladly

    gladly User title SILVER Star

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    :doh: overseas spec are different, I figured that if yours was four wheel drum it would be the same as a NA spec 4 wheel drum setup (older cruisers like mine) hard to tell that it is a split reservoir in the pic
    back to your regular scheduled residual valve discussion :D
  13. lostmarbles

    lostmarbles SILVER Star

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    No problems. The one pictured here is the original AISIN one that was on the vehicle when it left the factory. I've actually just removed an aftermarket PBR unit that did have 2 completely separate reservoirs (in order to refit the "reconditioned original"). But I'm having problems getting the original one to work again. =Which is why I started looking at those damned "thingies".

    My vehicle was actually assembled in Japan but most New Zealand cruisers arrived here CKD (completely knocked down) and were assemebled in NZ at the Toyota plant in Thames. I've noticed that these NZ-assembled models also tended to have the separate reservoirs fitted from new.

    :cheers:
  14. nuclearlemon

    nuclearlemon not an addict Moderator

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    the "single" reservoir is used on 60s with no issues. not sure why, but it is a factory thing'

    as to removing the valves, i've done multiple disc conversions and never had a problem locking up the tires without the valves there. i don't see a safety issue.

    and yes, if you don't remove them, they will lock up the discs...ask me how long it took me to figure that one out when i coverted magoo and forgot to pull the valve:doh:
  15. pbgbottle

    pbgbottle Forum Lifer SILVER Star

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    i don't no if this info helps .but i posted a question earlier asking about these valves and when looking up the part #'s for them for my master 78/fj40 front disc ,rear drum .converted to 4 wheel disc with no valves .i was thinking i should put some 2lb.s ones back in ,but when looking them up Toyota lists the same # for front disc valve as they do rear drum valve . so why would the master have the same valve for both front and rear circuit. these would be the plastic valve with spring and metal disc . not the drum valves lostmarbles posted

    http://forum.ih8mud.com/showthread.php?t=177075&highlight=residual valves
  16. lostmarbles

    lostmarbles SILVER Star

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    If you remove the "toyota-type thingies" -you will still be able to stop perfectly in any normal situation. Furthermore, no routine safety inspection will ever uncover any fault. You've misunderstood what I've been saying.

    I must assume that the "valve" you pulled was not the same type as the valves in my ex-factory mastercylinder. Mine CANNOT leave residual pressure in the brake lines because they incorporate a PERMANENTLY-OPEN bleed hole. Thus they CANNOT cause disc brakes to bind.

    :cheers:
  17. Trollhole

    Trollhole THC Moderator Supporting Vendor

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    I understand what you are talking about but don't know where you are going with this?

    You pull the risidual valves under the cups. Dependant on your setup. You never touch the other section where the brake lines feed into.

    How it works I don't know but it does.
  18. lostmarbles

    lostmarbles SILVER Star

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    Thanks pbgbottle. I am sure the part numbers would also be found to be the same for any mastercylinder that uses the same type of valve as mine. (I wish I could inspect those plastic ones to see for myself how they work and confirm for myself what they do.)

    I can promise everyone that my mastercylinder is indeed the original ex-factory one. And I promise also that the assembly of the components in this photo is exactly "as fitted" and that no-one has molested this mastercylinder by drilling those permanently-open bleed holes in the tops of those "caps.)

    labelled.JPG
    labelled.JPG
  19. lostmarbles

    lostmarbles SILVER Star

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    I'm trying to alert anyone who may have thrown away the same type of valves that are fitted to my mastercylinder that, in doing so, they have made their vehicle "much more unsafe". (If they don't mind this effect- Then that's their affair except I pity any unsuspecting future owners of their vehicles.)

    Like most people, I make mistakes. But I've learnt that a good way of avoiding most of mine is to try and "puzzle things out" as I go.

    If you blindly follow what others have done (or even what your Manual says to do), you will frequently get into trouble. That's my experience.
  20. projektdotnet

    projektdotnet

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    The residual valves for the NA 4wheel drum spec hold a higher residual pressure than the ones for disc brakes. Disc brakes do not have the same spring mechanisim that drum brakes and therefore do not push back as hard. The 10lb valves can, not always, cause issues with disc brakes not returning to rest due to line pressure remaining too high. You can either remove the one for the circuit that runs disc brakes (NOT THE DRUMS!) without problem. A 2lb valve is available to replicate for discs what the 10lb valve does for drums.

    At least that's what I have read.

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