Brake problem... Confused

Discussion in '80-Series Tech' started by hkimsoft, Jul 22, 2005.

  1. hkimsoft

    hkimsoft

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    Good evening;

    Just got OEM Brake Master Cylinder replaced. Bench bled and bleeded twice.

    Still feels very spongy and it sinks as you keep pressure on the pedal... Did the

    bleeding with engine off... feels very tight... then start the engine... feels very

    spongy again... any thoughts? should I keep bleeding? I've already used 4 bottles of

    toyota brake fluid...


    Thanks.
     
  2. flintknapper

    flintknapper

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    You've certainly started out right by bleeding the MC. Can you describe for us the process you're using to bleed the brakes.
     
  3. hkimsoft

    hkimsoft

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    First bleeding: RR, LR, RF, LF, LSPV
    Second bleeding: LF, RF, LR, LR, LSPV
     
  4. flintknapper

    flintknapper

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    O.K. but are you having someone pump and hold the pedal while you bleed the caliper, or are you using a "one man" device or perhaps a "mighty vac"?

    Sorry, I should have been more clear.
     
  5. hkimsoft

    hkimsoft

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    I am using traditional two men bleeding.

    Feels very tight and good after bleeding; But if I start the engine... it's very

    soft and spongy again...
     
    Last edited: Jul 22, 2005
  6. flintknapper

    flintknapper

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    Are you getting good clean fluid now at all calipers. Have your helper step hard on the brakes (engine off..no power booster) and look at each flex line (rubber hose) on each caliper and see if they are bulging under pressure. If not.. then it sounds as if you still have air in the system.

    For "two man" bleeding this is how I do it: Keep master cyl. full of fluid, use a clear plastic line to attach to the bleeder valve on caliper, pour an inch or so of brake fluid in a container and drop the end of the clear plastic line into it. Have helper pump brake pedal 8-10 times (or until resistance is felt) and hold pressure on it.
    Person at caliper slowly opens bleeder valve and watches for air bubbles.
    When the pedal reaches the floor have him keep it there until you can close the valve. Repeat until all air bubbles are gone and then move on to next caliper.

    I'm sorry for the remedial lesson, and it sounds like you already know this so please disregard if that is the case.

    If you have no leaks from around the seals on the caliper pistons, the lines aren't bulging, the MC is properly bled, and you're getting clean bubble free fluid at all calipers then I'm out of ideas.
     
  7. landtank

    landtank SILVER Star

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    I mentioned this in another thread, but I'll post it here as well. The rear calipers slide on pins. The pins actually bolt into the caliper and then they slide on the backing plte. They can bind up and not allow the caliper to slide to you are not clamping onto the rotor but instead just pushing it from one side. The mushy feeling is from flexing the rotor. I pulled the pins and then cleaned out the holes with a 3/8" drill bit. It seemed to be just the right size for the job. Be careful if you try this.

    To begin I'd pull the rear caliper and then insert the pins by themselves to get an idea of how easilly they move in the holes.
     
  8. flintknapper

    flintknapper

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    This is certainly possible. The pins go through a rubber boot that is supposed to help keep dirt and moisture from getting on them. Mine were very clean and still had lubricant on them but I'm sure the condition you describe can happen.

    It seems the pin or the bore would have to be worn to allow the caliper to get "cocked"..in which case it would indeed push against the torque plate.

    Good observation.
     
  9. landtank

    landtank SILVER Star

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    Just to add here also that my inboard pads where worn quite a bit more that the outters and had a wedge shape to them.
     
  10. hkimsoft

    hkimsoft

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    OK...

    Just had the brand new OEM rear brake pads installed (they were worn), pins inspected (they were

    clean), Inspected all brake hoses (all in good shape), once again bleeding continued... after another

    4 bottls of Toyota brake fluid... It's got even softer and spongy...@!@?@??@

    Could it be a booster? booster checks out according to FSM.

    Thanks.
     
  11. e9999

    e9999 You want to do what...? Moderator

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    did you do all the FSM tests about pedal depressing so many inches after so many tries etc? There are like 3 or 4 tests IIRC.
     
  12. hkimsoft

    hkimsoft

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    What are those 3 to 4 tests? I have a FSM downloaded from techinfo.toyota.com and can't seem to

    find tests other than MC and booster inspection...

    [EDIT] Pedal height, Pedal Freeplay, and Pedal reserve distance are all with in

    the spec.
     
  13. Rich

    Rich

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    Ok, I gotta ask. Why are you paying dealer prices for brake fluid? I guarantee you there is not going to be anything special other than the name printed on the bottle. Go the the auto parts store or the discount store of your choice and buy the big bottle of any name brand brake fluid for bleeding. If you are only topping up, then better to use the smallest bottle that will top up for you.

    There is a good chance you are just not getting all of the air out. Sometimes an air bubble gets in the right spot and the fluid just bleeds past it.

    I suggest the next step would be to go to a brake shop that has a pressure bleeder. The continous bleed will do better at moving a stubborn bubble of air.
     
  14. hkimsoft

    hkimsoft

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    thanks and I will try pressure bleeding. Will let you know what happens...
     
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