rear disk brakes not releasing

Discussion in 'Domestics' started by kettle, Jun 5, 2017.

  1. kettle

    kettle Full Member

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    Please fill out the following to ask a question.

    MAKE: jeep
    MODEL: Cherokee ZJ
    YEAR: 1996
    MILES: 152ooo
    ENGINE: 6 cyl
    DESCRIBE ISSUE....Rear disk brakes calapers are not releasing. Both rear wheels are sticking. Both rear wheels are restricted and get very hot. Vehicle can not be driven. I have disconnected the brake line from both rear calapers hoses . With this done I can compress the piston of both calapers, meaning calapers are ok. I opened brake line on the frame rail at the brake hose to rear axle and have a restriction between these 2 points. There is a splitter mounted on the axle shaft. The input hose goes into it 2 brake lines leave it. and there is a hose leaves it from the top . What is the purpose of this hose and where does it go? The splitter looks to be permanent mounted to the axle shaft. How do I remove it if I have to replace? The restriction is in the splitter or the hose feeding it. If anyone has had this problem with a jeep Cherokee please tell me about it. and trll me the purpose of the tube in the top of the splitter.
     
  2. billr

    billr wrench Staff Member

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    I can' t advise about that "splitter", but hoses often fail such as to cause a problem like you describe. The inner hose liner gets a small hole and the hose becomes a "check valve" that lets pressure get to the caliper, but not back out.
     
  3. nickb2

    nickb2 Wrench. I help when I can

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    Does your "splitter" valve look like this? I certainly hope not.

    Screenshot (71).png
     
    Last edited: Jun 6, 2017
  4. nickb2

    nickb2 Wrench. I help when I can

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    Here are more views, as for the "tube", that is most likely your vent tube for the differential. Tell me which picture resembles most what you have. One is just a rear view of the housing, the other just a front view. Commanche or cherokee of these times were exactly the same. Screenshot (72).png Screenshot (73).png
     
  5. nickb2

    nickb2 Wrench. I help when I can

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    My thought is, the "splitter" goes to load compensating valve which is either bad, or adjustment off, keeps pressure amplified ALL THE TIME to rear. I really can't see anything else.

    Was very common actually when I was working for mopar.
     
    Last edited: Jun 6, 2017
  6. nickb2

    nickb2 Wrench. I help when I can

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    Normally, that splitter valve is an integral part of the axle tubes and never goes bad. Usually, it's the compensator
     
  7. kev2

    kev2 wrench

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    My guess it is is the hose - from chassis to differential.

    The 3rd hose - could it be the diff vent hose ? Visible might be a different type of hose ?

    GTG
     
    Last edited: Jun 6, 2017
  8. jd

    jd Hero Member

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    Change the hose, for sure. Cheap and often it's the problem. Look for any steel brackets/clamps/guides that hold the hose in place, or away from moving parts. If you find one, loosen or remove and look for rust festering up and squeezing the hose.

    It's good you aren't driving it. Let me mention this odd case. Strange but it happened to me. The Master Cylinder has two vent holes per chamber, meaning two front and two rear. One of the two is large and allows the reservoir to fill the cylinder when the pedal is released. The second is very small, farther into the piston stroke. It's there to allow any pressure in the system to bleed down, back into the master cylinder reservoir. On a Toyota with an aluminum master cylinder, that little bleed hole "healed up" with corrosion. As the car drove, the system got hotter and actually started applying the front disc brakes at highway speed, without touching the pedal. Since each front wheel had a hose, and loosening either bleeder relieved the pressure, I decided to dismantle the master. Took me two tries to spot the little "scab" in the bottom of the reservoir. Took it apart and cleared the hole with a little number drill. Ran a hone across the area inside the bore to make sure I hadn't put a burr where the piston seal cup would run. Solved the problem.
     
  9. kev2

    kev2 wrench

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    My 2$.02 in nicks pictures above - the differential has the block 2 metal lines 2 flex lines - that should be your set up - am I right?
    metal are obvious brake lines L and R.
    flex are 1 brake line chassis to block the suspected issue.
    other flex is diff vent - jeep type to keep out water for the off road types.
    Am I close or again way way off?
     

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    Last edited: Jun 6, 2017
  10. Mobile Dan

    Mobile Dan wrench

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    [​IMG] The "splitter" is part of the rear Axle-to-frame brake hose. It is held to the axle with a single bolt. Sometimes, the bolt is hollow and has the axle vent hose attached to it.[​IMG] [​IMG] [​IMG]
     
  11. NickD

    NickD wrench

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    Two brand new vehicles in the family, first post production work was to look at the brakes, for eight caliper guide pins, only one or two were properly lubricated. Fill those with silicone, especially in the boots to help block road salt from getting in. Also pop off the boots on the pistons and fill those with silicone as well to help block road salt from getting in to seize the pistons.

    Most are using torque plates or pad brackets, have clips on them that can trap road salt, expand and seize the pads. they get coated with anti-seize. Pad backing plates are painted, should be plated, rust builds up on the tips that jam them in those clips, more anti-seize. Remove the rotors and anti-seize the mating surfaces to the hub. Ever spend two hours trying to remove a rotor?

    Actually my youngest kid spent a winter in Milwaukee, they really pour on the road salt, all four wheels had major drag with a new Soul, that was a job cleaning. needed to use a puller to get out the guide pins. Has those cheap rear disc with that combination service and parking brake, those levers were not even close to getting to the home position. On some of this new crap, using an self adjusting parking brake, another bad joke, but hers had a nut on it, so could loosen that.

    When on the interstate, like to stop for gas or a rest area, just take a quick walk around holding the back of my hand to each wheel, if I feel heat, know I have a problem.

    Sure love my 88 Supra, uses conventional calipers on the rear wheels with drums for the parking, inherently self adjustable just like on the fronts. These combinations are a PITA, and not even my dealer knew you had to work the parking brake for adjustment. And replacements are way overpriced. Toyota did invent those torque plates, can't use a C-Clamp on rear disc calipers, most copied this, but not the separate drums for the parking brake.

    Newest problem are these super cheap ABS modules, hardly a four inch sized cube with a slot car sized ABS pump motor on it. Now you need a scanner to activate that ABS pump for proper bleeding, but the shop manual states, only for short periods of time or else you will burn up that POS motor. What a joke ever since our AH congress made this law. Another bad joke is TPMS.
     
  12. billr

    billr wrench Staff Member

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    Yeah, I sure agree with you about how cars are now over-burdened with stuff like TPMS, ABS, SRS, traction control, active suspension, infotainment, Big Brother logging, etc.

    I and my cars are getting to the age when a new car is probably going to be needed, but I am resisting because of all that crap I don't want, that I will have to accept.
     
  13. JackC

    JackC wrench

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    Agree. I may be able to get through this life with my old vehicles.
     
  14. kettle

    kettle Full Member

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    I Thank you guys for all the replies. They were all helpful to me. especially the pictures. The hose I was asking about was a breather hose for the rear end. The problem was the hose from the frame to the splitter, which are made together. It was acting like a check valve. I replaced it and now the brakes work as they should. I Want to thank you guys again. I always go to BAT when I have mechanical problems that I need help with and you guys have always been able to help me. Thanks again.
     
  15. jd

    jd Hero Member

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    Good news! Glad you're running again, and Thank YOU for the update!
     

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