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DOT 3 or DOT 4

Discussion in '40- & 55-Series Tech' started by ktjensen, Jan 23, 2003.

  1. ktjensen

    ktjensen

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    I have a weird intermittent problem with my brakes over heating. It has happened on two events that I went to last year.

    First time (new Cruiser owner of a 1994 FZJ80) the brakes went to mush after a long drive decent down a mountain. I looked at the fluid and it was dark (maybe burnt?). After cooling all was okay for the drive home, and for the rest of the weekend.

    I had someone do a passive drip flush of the brakes a week later. Then I went on another trip.

    I did get some mushy brakes after a long decent, but not as bad as before. The fluid did turn dark again. I am thinking I need a power brake flush with DOT 4 fluid.

    Any other possibilities?
     
  2. ledge

    ledge

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    Are you talking about on the trail, or on the road? If you are on the road I cant answer your brake problem, but as a CO resident who drives in the mountains all the time I can tell you to get off the brakes on your decents. Use your gears to hold you back, and you wont have to worry about braking as much. If it was on the trail I would also think that gears should be enough with only minor use of brakes.
     
  3. petescoffee

    petescoffee

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    Have had similar problems in my 3/4 ton truck when towing down a long steep decent when I was fully loaded and towing a trailer. The Brake fluid had boiled. Learned what a emergency break is really for. Changed to Synthetic fluid and it did not boil, but gave a different feel to the brakes. Eventually just used Dot 4 and did not have a problem. I carry extra Break fluid when off road now and can change it easily just in case it happens again.
     
  4. Erics75

    Erics75

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    Brake fluid is "Hygroscopic" which means it tends to absorb water. The water in the brake fluid is what actually causes the boiling problem becuase it lowers the boiling point of the fluid. Keep the system clean by periodic flushing, I usually do it every couple of years and if you want to spend the money switch to DOT 5 which is silicone and it won't absorb the water like DOT 3 or 4 and the boiling point is much higher. I've never heard of a passive drip flush, but using a pressure bleeder probably works better than anything and it might get rid of any moisture trapped in your calipers and cylinders.
     
  5. cruzila

    cruzila

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    Yes, the dark may be coming from the rubber in the system. As it deteriorates, it will put rubber into the fluid making it darker.

    The boiling previously mentioned is covered but I would add that if you go to DOT5, CLEAN the entire system, NEVER add any other type and carry spare fluid as it may be hard to find.

    I use DOT 4 and flush regularly. I wheel in water and mud at times so this is needed.

    Scott
     
  6. ktjensen

    ktjensen

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    I replaced the master cylinder because I thought it was the culprit. I still am having problems with mushiness.

    Forgot to mention that this has ABS, and I can not lock the brakes (with ABS turned off with center diff lock switch) no matter what I do. ABS worked in the snow.

    Kev
     
  7. 74cruiser

    74cruiser

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    juat adding another brake question regarding mushey brakes, i have the same problem, i replaced the master cylpider and rebuilt the calipers, now instead of the breakes heating up and seizing they are mush and dont want to stop, what is the best way to flush out the brakes and make sure there is no air in them at all, also mine being a 74fj40 i have 2 resavors, the front (the one i cant get to work) is clear and the rear is dark.
     
  8. Guest

    Guest Guest

    The 'Mushieness' could also be from over heated Brake Pads, Easiest way to fix this is to put Grooved Rotors on and go to a Brake Pad with more Metel in it.
    Dad went from Bendix Standard to Benix 4WD and now the Rotors do not get glazed on his FZJ80R.

    Could install a Exhaust Brake or get the Head changed on the 1FZ-FE to one that has a Jake brake mechanism. :slap:
     
  9. Erics75

    Erics75

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    Hi 74cruiser, when you replaced the M/C did you bench bleed it? This process gets rid of air that may be in the M/C, this should be done while it's mounted on the vehicle to prevent over stroking and damaging the rubber cups on the compensating ports. here are instructions I found on web.
    http://www.misterfixit.com/brakbld1.htm
    Like I said, it can be done on the vehicle, and because I have seen the cups get damaged by overstroking in a vise, its a better method for your application.
     
  10. 74cruiser

    74cruiser

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    yes i bleed the MC and i was mostley working fora bit, the brakes sometimes over heated, but the worked. then i had to disconnect the brkaes lines from the front caliper to do some work and ever since then the front brakes havent been working. i bleed them as best i could, but they still went working so i rebuilt them no i have to figure out how to get all the ait out again, and see if they work. whats the best way to makesure all the air is out besides pumping and releasinng the brakes w/ 2 people.
     
  11. 3_puppies

    3_puppies SILVER Star

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    I've bled brakes solo. I hook a clear plastic line up to the bleeder screw, then stick the other end into a container with a little brake fluid in it. As you pump the pedal the fluid goes into the container, air bubbles come out and fluid goes back in. With the clear line you can see that all the bubbles are out. Then tighten the bleeder carefully as to not break the seal and let air in.