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Cat th83 brakes

Discussion in 'Forklifts/Telehandlers' started by Moonlite, Dec 20, 2015.

  1. Moonlite

    Moonlite Senior Member

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    I replaced the brake disks and booster cylinder. With out the machine running the pedal goes all the way to the floor but I can get fluid at the bleeders on the axle. With the machine running the pedal will pump up but I have no brakes. With the machine running I can't gett fluid to the bleeders on the axles. I talked to cat tech service and was told to replace the booster cylinder so I did. I still have the same problem. I am getting 400 lbs of pilot pressure to booster. I called cat back and they sent me the bleeding procedure. The master cylinder resivoir I have is sealed and has 3 lines on it. What they sent me is for a reservoir with a cap and one line on it. They call for drilling a hole in the cap and filling with 10/30 motor oil. then a set up a conglomeration of stuff. But I have sealed reservoir that fills with hydraulic oil when I hit a function? Anybody got any other info? Thanks
     
  2. Moonlite

    Moonlite Senior Member

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    SER is catoth83h3rn04481
     
  3. Nige

    Nige Senior Member

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    Question: Why did you replace the brake discs..? Worn out..?

    So if I understand you correctly you replaced the booster cylinder along with the discs then at the recommendation of the dealer you replaced the booster again with another one, right..? Were both the boosters you installed new..?

    Is there any possible way you could have got the fluid piping connected incorrectly when you installed the brake booster cylinder..?
     
  4. Nige

    Nige Senior Member

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    A couple more questions. When you replaced the discs did you readjust the brakes..?

    Also regarding your brake fluid reservoir. Is yours like the one on the left or the one on the right of the illustration below..? If it's the one on the right then that is the old version, the updated one is the one on the left. The new one can be retrofitted quite simply in just a few minutes and enables you to use the brake system bleeding procedure that the Cat dealer sent to you.

    TH83 Brake Reservoir.png
     
  5. Moonlite

    Moonlite Senior Member

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    Originally it had brakes just not very good. The ring gear and pinion on rear diff was shot. So we pulled it down and found disks worn. So we ordered new ring gear and pinion brakes disks and all the prongs to reseal brake pistons ect. I could only get fluid to disks with machine not running. So I called cat tech service and explained what I had done. They told me to check my pilot pressure to booster and if I had close to 400lbs replace booster.
     
  6. Moonlite

    Moonlite Senior Member

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    image.jpg

    This is what my reservoir looks like. The big hose refills it when I hit a function. The little line goes to master cylinder. There is a 3rd line that I haven't traced yet.
     
  7. Moonlite

    Moonlite Senior Member

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    I did replace disks and orings on all four axles
     
  8. Nige

    Nige Senior Member

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    Did you adjust the brakes after replacing the discs..?
     
  9. Moonlite

    Moonlite Senior Member

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    Yes I did adjust the brakes. When I had the axles and after new disks were installed I bottomed out each adjuster bolt. Then I backed each one off a 1/4 turn until I could turn the axle.. Total was 3/4 to 1 full turn. My problem is I can't get fluid through booster when machine is running. Is it possible the master cylinder is not putting out enough pressure to activate the booster ?
     
  10. Nige

    Nige Senior Member

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    If you have already replaced the booster twice with no result the possibility is there. Why not try disconnecting the line that supplies oil from the master cylinder to the booster and pump the pedal to see what happens..?
     
  11. Moonlite

    Moonlite Senior Member

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    I have only replaced booster once. I did pull the inlet line off and had someone pump pedal. I couldn't hold my finger over the end. When they were pumping it. If I was to adapt a gauge to it how much pressure should I have?
     
  12. Moonlite

    Moonlite Senior Member

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    The booster has 4 lines in it. Inlet outlet pilot and tank. I assume the tank line is a return?
     
  13. Nige

    Nige Senior Member

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    Here's the schematic of the TH83 brake system along with the text to go with it.

    TH83 Brk Sys Schematic.jpg

    1 Brake discs
    2 Pilot valve
    3 Pressure switch
    4 Brake cylinder (boost)
    5 Brake cylinder (master)
    6 Hydraulic tank
    7 Brake reservoir
    8 Parking brake switch
    9 Lever (parking brake)
    10 Cable
    11 Joystick control

    The brake pedal is connected to a mechanical linkage in order to operate brake master cylinder (5). When the brake pedal is pressed, oil pressure is transmitted from brake cylinder (5) in order to operate brake cylinder (4). The operation of the brake cylinder (4) creates high pressure oil which is transmitted through the brake lines in order to engage the brake discs at each axle.

    The operation of brake cylinder (4) is assisted by boost pressure from the implement pilot system. The implement pilot system is connected to the brake cylinder (4) from pilot valve (2). The brake master cylinder (5) is automatically topped off with oil from the brake reservoir (7). The brake cylinder (4) is automatically topped up from oil from pilot valve (2) .

    Pressure switch (3) is used in conjunction with the transmission neutralizer control (switch) on the dash panel to disengage the transmission when pressure is applied to the brake pedal. When the transmission neutralizer control is engaged, the transmission is engaged at the speed which was previously selected. Parking brake lever (9) is connected to cable (10) in order to operate the brake discs in the front axle. Parking brake switch (8) enables the transmission to disengage when the lever for the parking brake is pulled slightly upward.

    One way to tell if you are getting enough pressure from the brake master cylinder. Does the transmission disconnect like it's supposed to when you press the brake pedal..?
     
  14. Moonlite

    Moonlite Senior Member

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    Thanks for all the help Nige
     
  15. Moonlite

    Moonlite Senior Member

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    Again thanks nige for all the help. Replaced master cylinder and the reservoir I broke. Being that the reservoir was sealed on this one . I pulled the line off that went to the master cylinder and adapted a qt bottle full of cat hydraulic oil turned it upside down. The put a hose long enough to reach the cab from the bleeder screw on the booster cylinder. Pumped the pedal until I got fluid out of the hose attached to booster cylinder. Closed off that bleeder then pumped up the pedal and then blocked the pedal down and opened the bleeders on each axle one at a time.. Now it has brakes.
     
  16. Moonlite

    Moonlite Senior Member

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    One thing that made a difference I got this thing off of the job and drove it the 2 miles to my house where people weren't standing over me asking are you gonna have it ready to day so the guy can load it and get it out of here. Finally told them yesterday that it was leaving yesterday by driving it or hauling it.
     
  17. Boe

    Boe New Member

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    I'm having the same problem with my cat th83 and I guess I'm not understanding what made the difference as far as what he did to fix it
     
  18. Moonlite

    Moonlite Senior Member

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    I just bled it real good after replacing the master cylinder
     
    Tarhe Driver likes this.
  19. lawrence517

    lawrence517 New Member

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    wht is the part number associated with that booster? im having the exaCT ISSUES
     
  20. Nige

    Nige Senior Member

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    Posting your machine Serial Number might help in some small way to identify the necessary Part Number for your machine. Otherwise it's a cr@p shoot.