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Thread: Bleeding hydraulic-air brakes?

  1. #1
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    Bleeding hydraulic-air brakes?

    Ok this may sound like a dumb question, but I am stumped. How do you bleed hydraulic air brakes? I have never bled this type of system before and don't know where to start, or what the problem is. The machine is a late 80's model W14B wheel loader. It all started when i busted a brake line on the front. When I went to replace it, I noticed the back 2 brake lines were disconected/ missing . I ended up replacing all of the lines that were bad, and filled it full of fluid. Now the question is what method do I use to bleed the entire system? Nothing has seemed to work so far.

    Thanks Brandon

  2. #2
    Charter Member RonG's Avatar
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    It seems as though you could gravity bleed them if the reservoir is above the wheel cylinders.I have bled Cat loaders that way.If not you might try the vacuum method.
    Let us know what you have tried so far.Ron G

  3. #3
    Member GOINGBROKE's Avatar
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    I found a tool called Phoenix injector http://www.brakebleeder.com/product.php?pid=2
    it pushes the brake fluid backwards from the wheel cylinders, pushes the air out and fills the resivor. The only thing that I have found that works to bleed some clutch slave cylinders on some tractors.

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    I have messed with it a little, but not extensively. Our neighbor's son-in-law is familiar with heavy equipment and messed with it quite a bit one day, with no luck. It has a air tank that connects to the master cylinder. The pedal in the cab is different than bleeding like a regular tractor or truck because of the air assist. It has no good way of "pumping" to build the pressure and hold like you would in a non-air assist system. I'm sure that I am just doing something wrong. I have tried filling the resovoir and hitting the pedal to the floor while someone breaks open a bleeder, and then closing it after fluid comes out. This hasn't woked, but I haven't had the chance to work on it for a few weeks now. I will try to get a bleeder, like the one on that website, and try that method out this weekend or next. I can't gravity bleed them easily because of the way the lines are ran.

    Thanks Brandon

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    O also the front wheel calipers have two bleeder screws. Not real familiar with this setup. I assume I bleed the screw closest to the brake line first on each caliper, and then open the second screw after the first one is bled good? Is there any good pages that show step by step process to brake bleeding on the internet for air assist brakes?

    Thanks Brandon

  6. #6
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    Lack of brakes

    It would be wise to check out the Master cylinder, it sounds like it needs a re-seal, I do not know what a W14B is??? but near all loading shovels have 2 line brakes, one for the front axle and one for the rear, fed from 2 master cylinders or 1 tandem cylinder, if its an air over hydraulic system the min air pressure needed would be 65 psi, the usual max working pressure would be 120/125 psi, lots of calipers are fitted with top and bottom bleed screws, this is so 1 caliper does both left and right side wheel station, the only bleed screw you need to be fiddling with is the top/highest one, I always use a water pressure test kit to help me to bleed out a brake system, I fill the fluid pot up, then screw on a test fitting in place of the pot cap, then open a bleed screw a bit and hand pump a few psi into the pot, then do up/undo any other bleed screw/s in the system, I always start on the closest bleed valve to the master cylinder, lots of service manuals say start at the furthest bleed valve, I stick to what works for me and gets the job done, if you use a pressure in the pot system to bleed the brakes, you dont fan the brake peddle and get other people involved in what can be a mucky old job if they pump the peddle at the wrong time, so re-seal your master cylinders and it should work great.

    tctractors

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    Thanks will give it a try this weekend or next when I get the opportunity.

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    Quote Originally Posted by GOINGBROKE View Post
    I found a tool called Phoenix injector http://www.brakebleeder.com/product.php?pid=2
    it pushes the brake fluid backwards from the wheel cylinders, pushes the air out and fills the resivor. The only thing that I have found that works to bleed some clutch slave cylinders on some tractors.

    I found this reverse bleeding the easiest way to bleed the brakes on the older cat loaders, just make sure that the wheel cylinder bleed screws are clean, or you'll end up with crud in the wheel cylinder.

  9. #9
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    You bleed these systems just like you would a manual system. Fill the reservoir, push down on the brake pedal and hold it. Now crack the bleeder open until you hear the air stop rushing through the fitting. Close the fitting and then let up on the pedal. Wait a couple of minutes to make sure the master is all the way back and then do it again.

    You start at the furthest fitting from the master. When that fitting has oil go to the next furthest.

    From my experience all those brake system components were manufactured by Bendix Westinghouse. You can probably find rebuilt units at your local Napa store instead of doing the dealer parts. They are not very complicated at all.

    You might check that the master cylinder is moving at all. I've seen them frozen completely solid at the end of their stroke because they have sat so long with no fluid in them.

    Good Luck!

  10. #10
    Senior Member Cmark's Avatar
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    I agree with John C. Especially if, as you say, a brake circuit has not been working for a long time then a siezed M.Cyl is (almost) guaranteed.

    Strip and rebuild all your master cylinders and then use conventional brake bleeding techniques. Just remember to pause a little longer between pedal strokes as an air-over-hydraulic system needs to vent its air pressure to allow the M.Cyl to return to the start of it's stroke.

  11. #11
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    Balky brakes

    Separate the master cylinder(s) from the actuator to see if the piston is stuck at the bottom end. We have an older CAT that leaks fluid and if it gets empty than this seems to happen.

  12. #12
    Probationary Member vbe75's Avatar
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    Not sure if this will help, i am not familiar with loader brakes. On my 5 ton 6x6 the brakes are air-hydraulic. The air assist pak has two fittings on it that you need to bleed the fluid from before you go to the wheel cylinders.

  13. #13
    Senior Member Iron Horse's Avatar
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    You will more than likely find that the rear brake lines were removed for a reason , you may have re-created an old exsisting problem by re-connecting them . Also what can happen is that the piston in the master cylinder has been stopping in the same position for years . When the brakes are bled after working on the system , the piston is forced past this point . This can damage the cups as they are forced over a ridge or over a dirty/rust pitted area . A re-sleeve and a full overhaul is then needed . A method i have used on hard to bleed trucks and machinery is to buy a new pump up weed sprayer , the kind with the hand pump on top ($20). Put a litre of fluid in it , take off the wand and push the hose over the bleed nipple on the furthest calliper and open the nipple "slightly" . Push the trigger on the sprayer which forces fluid and any air up the lines and into the resovoir . Be aware that the resovoir will overflow so if necesary , put a tin under it to catch the fluid or just hose off the machine later .

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