Bleeding a disk brake 404
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Thread: Bleeding a disk brake 404

  1. #1
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    Default Bleeding a disk brake 404

    Hi all,

    I am trying to bleed the brakes on the 404 and I am not winning. I have checked that the master cylinder is moving freely and is pumping well, but I am only getting the tiniest trickle at the rear. The weight is on the rear axle so I don't THINK the limiter is the problem.

    I am getting no significant back pressure at the master.

    I wonder should I progressively bleed between the master and the booster?

    Advice gratefully accepted.

    Matt

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  2. #2
    Fellow Frogger!
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    You probably have a frozen proportioing valve at the rear that will not allow propper flow to the rear cylinders or you have a problem with the rear hose.
    I can supply you a reconditioned valve exchange for $140 plus post
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  3. #3
    1000+ Posts Beano's Avatar
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    As Ian has said, the limiting valve does freeze up, and 404s are getting old.

    Are you getting ANY fluid coming out of the bleeder nipples ? In the past I have unscrewed nipples and found that the tiny hole at the inside end has been clogged / rusted up. Try that...

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    I'd crack a flare nut before the diff hose, and progressively move towards the brake rear cylinders.

    The item before the flare nut that doesn't flow is the stoppage.

    I'd also check the master cylinder is pumping fluid by cracking the flare nut at the booster inlet.

    All bets are off what is working or not working on a 49 year old vehicle - you need to fault find or better still check each item in the brake system and replace/ recondition as required.
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    Quote Originally Posted by Beano View Post
    As Ian has said, the limiting valve does freeze up, and 404s are getting old.

    Are you getting ANY fluid coming out of the bleeder nipples ? In the past I have unscrewed nipples and found that the tiny hole at the inside end has been clogged / rusted up. Try that...
    Once you see this happening, the whole system is getting very tired and needs a refurbish. Need to keep up with the autonomous braking systems on new cars
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  6. #6
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    What about the front end ?
    Any fluid coming out there?

    Sent from my GT-I9505 using aussiefrogs mobile app

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    Hello Matt,

    Was this a running car or a sleeper?
    Like Beano advised go for the nipples first, they tend to get clogged up. If still persist than would suggest you unplugged the flexible hose attached to the torque tube in picture one. This hose also has a tendency to get block. I think from here roughly you can figure which directions to go.
    Bleeding a disk brake 404-20171104_121538.jpg
    Last edited by peugeotnut; 4th November 2017 at 04:05 PM.

  8. #8
    1000+ Posts Beano's Avatar
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    Yes, that flexible hose feeds both rear brakes (at least in 504s). And in case you're wondering, they don't get clogged up with dirt or anything....they collapse internally.

    But go for the nipples first

    Did that model 404 have single circuit brakes ? Because the master cylinder could be stuffed.
    Early 504s had single circuit brakes, so I am assuming that 404s certainly did.

    If they ARE single circuit and the master cylinder has not been replaced or resleeved in the last few years, I HIGHLY recommend doing so. It is truly frightening to lose all braking....both front and rear at the same time.
    Resleeving in stainless, together with new seals will cost about $140 for a 504, and less for a single circuit 404. Perhaps as low as $80

    Often resleeving is about the same price as a new one.....dependent on how much you shop around.
    Last edited by Beano; 5th November 2017 at 02:26 PM.

  9. #9
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    All 404's in Australia (Right hand drive ) were single systems. The later European versions had a twin system. More space in the engine bay. The brake booster in Australia, Hydrovac were the same version as being used in the earlier European drum brake versions. They also had a back up vacuum tank. With the cracking of the line nuts, that is a good idea. But make sure you also check the exit pipe from the booster. The valving/cups in the booster (If it is an original) may stuffed as well. This will prevent fluid from entering the rear lines.

    Have you tried the front calipers. Do they release fluid. If so, that would indicate that there is nothing wrong with the master cylinder. Operationally anyhow.

  10. #10
    1000+ Posts robmac's Avatar
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    But make sure you also check the exit pipe from the booster. The valving/cups in the booster (If it is an original) may stuffed as well.
    My experience is the power booster is often full of non specific semi fluid black goo.

    So invert the booster and drain extraneous fluid. It's likely to have ruined the booster diaphragm. Which is a very expensive repair if it happens to still be a Girlock unit.

    In this case the cost effective option is to replace the booster with PBR VH24. Which is smaller and screws to the same hoses.

    You can eliminate future goo inside the booster, by ensuring the vacuum hose is routed to curve above the carby, if you don't excess fuel from the carby drains into the power booster via the vacuum hose. Which , I believe ,is cause of goo in the first place.
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