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Dangerous Brake Problems

Discussion in '80-Series Tech' started by Tooth Fairy, Jul 29, 2005.

  1. Tooth Fairy

    Tooth Fairy

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    I don't know what's causing this, but, I drove her 80 t'day and it scared the crap out of me.

    What I've noticed;
    Seemingly random loss of pedal pressure.
    Sometimes it will stop fine and other times I have no brakes.
    ABS activates and I have no stopping at all.
    Maintains pedal pressure when engine is off.
    Pedal almost goes to floor when engine is on.
    Pumping the pedal doesn't seem to make a difference.
    Brake fluid level is high and doesn't change.
    No leaks.
    Newer OEM rotors on the front and 100 pads.
    Newer aftermarket rotors on the back w/ new pads.
    This appears to have come on slowly, but, is increasing in frequency.
    Disabling ABS mkes no difference.

    My initial thought was that my aftermarket rear rotors were not thick enough and therefore I needed more pedal movement to engage the pads.

    Then when I tested the pedal pressure with the engine both running and not I am now wondering if it's possibly a brake booster problem because that would only be active when the engine is producing vacuum. The other thing I was thinking is that it could be master cylinder issue. Once again there isn't any fluid leakage either inside or out.

    Whadya think?
     
  2. 92FJ

    92FJ

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    I tihnk you should replace you master cyclinder and bleed teh brakes. The porblem should go away
     
  3. Romer

    Romer fatherofdaughterofromer Moderator

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    I am assuming you checked your brake fluid level?
     
  4. IdahoDoug

    IdahoDoug

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    Romer,

    I'm assuming you read his post? The part where he says "Brake fluid is high and doesn't change"? Heh - feeling frisky tonight.

    Someone recently cured a problem similar to this on the 80sCool list by replacing the rear pads/rotors and they felt it was a thickness problem. I'm not sure I agree with the cure, but it worked. He had replaced the MC and booster I believe and had repeatedly bled things.

    If I were you, I'd do a very meticulous bleed that included some serious volume out of the RF when it's that caliper's turn to be bled as it does sound a bit like air in the system from some perspectives, though not all your symptoms. I'm sure you've done this, but do you have any vacuum lines loose? Double check the little ones you can barely see under the intake manifold between the runners for cylinders. Look at the brake line coils over the left inner fenders and straight inboard of this you'll see a device with what looks like a blue button on its rear end. Above and forward of this are several short vacuum lines I've found unhooked on 3 different 93 80s. If disconnected, they require a bit of finger contortion to get back on their nipples.

    DougM
     
  5. Aussie cruiser

    Aussie cruiser

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    Check your wheelbearings loose or stuffed bearings can cause to pedal to go soft. I had it happen when a bearing seized and collapsed
     
  6. lovetoski

    lovetoski SILVER Star

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    CruiserDan has posted how loose wheel bearings can give wierd brake symptoms. His advice solved a problem on my 60, proving again that he's a god...

    Back to the orginal problem though...this is a case where my approach would be to eliminate everything that's free/cheap to fix/check. For example, doing a really thorough brake bleed makes sense. I found that the LPSV is a biatch to get air out of, and it took multiple bleeds to get it (and the rear brakes) free of bubbles. Much better when I was done.

    Also wouldn't hurt to check bearing play, who knows, CDan might be right again.

    Next would be to use the FSM to check the function of the brake booster.

    If after all of these, you still have problems, it's time for the beverage of your choice...
     
  7. IdahoDoug

    IdahoDoug

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    Seconding the bearing checks F/R - excellent advice. Order the rear seal kit from Cdan. Just did both of mine a couple weeks ago and you can avoid draining the diffy by jacking each side of the axle in turn high enough to keep oil from flowing out. Much more pleasant that way.

    DougM
     
  8. Kalawang

    Kalawang

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    I'm more inclined to believe your pistons in the MC have worn out and need replacement. Most any mechanic should be competent to change them if needed. Pull them out and check the rubber collars for wear and tear. If you find it damaged, check the MC for scratches.


    Kalawang
     
  9. powderpig

    powderpig SILVER Star

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    I would first pull the ABS fuse to see if it is a ABS problem or a mechanical problem. As well as checking the wheel bearings. If your problem goes away with the abs fuse pulled then you have some ABS problems to check out . later robbie
     
  10. Romer

    Romer fatherofdaughterofromer Moderator

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    Sorry, just got back after having 3 Crown Royals and a nice big Cigar.
     
  11. IdahoDoug

    IdahoDoug

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    Ken,

    Hee, hee, hee....

    Robbie,

    More "non reading" of his post? He mentioned disabling the ABS and ruling it out. I think you guys are padding your post counts - heh. As am I....

    DougM
     
  12. Rogorn

    Rogorn

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    My vote would be for worn rubber cups/plungers on the master cylinder pistons.

    My daughter's '87 Camry had intermittent braking problems. Soft steady pressure caused pedal to sink to the floor slowly. She was taught to brake with light pressure - (translation, let the weight of the vehicle bleed off speed) - versus the way my son does it! (hard and quick...)

    Okay, back to the point, she started losing pedal, which was scary for her. The pedal would sink to the floor and pumping pedal restored braking. Sharp, hard use of pedal had plenty of braking and eliminated the need to pump.

    Hypothesis:
    The rubber in the master cylinder would leak when soft pressure was applied, allowing brake fluid to seep around the rubber, poor contact with walls of the cylinder, etc. Where as, sharp or hard braking would keep the rubber flared against the walls and reduce amount of leakage.

    Replacing master cylinder with after market restored firm solid pedal. (Sure, I also did wheel cylinders, new shoes, front pads, etc...)
     
  13. Tooth Fairy

    Tooth Fairy

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    Thanks for all the input . Even you guys that didn't read my 1st post. :flipoff2:

    I have decided to take it back to ID with me rather then leaving it sit here for a month.

    One other thing I was going to try was disconnecting the vacuum line on the booster to see if that makes any difference. It held pressure with the engine off for 1 minute, so, that doesn't really seem like a MC problem.

    I don't know.

    When I make it (if I make it :rolleyes: ) back to ID I'll start with some more things and let you know what I find out.

    Butch
     
  14. Kalawang

    Kalawang

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    Disconnecting the hydrovac only makes the pedal harder to push and does not make the stopping better. It's an illusion. It's also dangerous to try traveling with defective brakes. I truly suggest that you get those brakes fixed as close to where you are as you can handle.


    Kalawang
     
  15. Cube Dweller

    Cube Dweller Moderator

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    I had an intermittent pedal to the floor issue on my runner. Sometimes soft, sometimes fine, seemed to vary at random. Ordered a new brake master, when I pulled the old one you could see fluid leaking from around the rod, so i assume the piston seals were leaking. I didn't disassemble to check what was worn.

    New master solved it. Apparently the PO had replaced it already with a Kragen special, I went OEM.
     
  16. Tooth Fairy

    Tooth Fairy

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    You didn't understand what I was saying. It's just a trouble shooting measure and besides, the brakes are already defective, so, I don't have anything to loose.

    All that doesn't matter anyway because I fixed it. :D

    IDAHODOUG is the winner. You know I've seen those little bitty vacuum lines fall off under the intake once in a while, but, never at the expense of braking power.

    Thanks Doug!

    -Butch
     
  17. Bear80

    Bear80

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    so it turned out to be a vacum line? Was it lose, off, broken?
     
  18. Tooth Fairy

    Tooth Fairy

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    Yeah it was just off. That little line has had a tendency to fall off since I have owned the rig for the past 4 or 5 years. I've always noticed it was off before it ever acted weird though. It's right above the oil dipstick.


    Thanks again to all you guys for the help and Kalawang I didn't mean to come across as a prick. I just reread my post and it sounded a little harsh. No malice intended. I also trust no one else to work on my junk, so, that has something to do with my response.

    :D B...
     
  19. Vitesse_6

    Vitesse_6

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    Sorry to bring up an old thread, But could you remember if it happend more when it was up to running temp? I have had some issues of late Im trying to see where to start.
    I will check what I can ASAP from the list of things above.
    Thanks for any other info.

    Edit.
    Sorry I forgot to mention I have replaced the front rotors and pads and adjusted the rear "DRUM" brakes a month ago, I have been wondering IF I need to recheck/clean the TB.
     
    Last edited: Dec 1, 2005
  20. Tooth Fairy

    Tooth Fairy

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    Didn't make any difference whether it was cold or not.

    Adjusting the right front wheel bearing was all it took. I have had zero problems since.

    B