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Why don't my brakes work?

Discussion in '40- & 55-Series Tech' started by dentedpig, Mar 25, 2004.

  1. dentedpig

    dentedpig

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    Well hello there, I've been a lurker for quite a while, and finally feel the need to post. I have a 1969 FJ55 that I just put minitruck disc brakes onto. I'm using the hard parts and booster from a 1983 pickup. the rotors are from and 81 FJ40, and the Master cylinder and calipers are from a 1990 4x4. I'm also using the hard lines from the 1983 truck for the front brakes, and have maintained the original 1969 brake line for the rear circuit. I just finished getting everything together, and to my dismay, these brakes just don't aren't working too well. When the truck is not running, the brakes feel normal, but when the truck is running, there is very excessive pedal travel before the brakes are actuated. The brakes appear to work, but resistance is only felt once the pedal gets almost to the floor. This does not match the symptoms of a bad booster. Anyone have a guess of what is wrong? Is the 1" master cylinder too small to run this combo of brakes, does it have the wrong size residual valve? I have not tried driving it yet, as I am waiting on a machine shop to shorten and retap my relay rod.
     
  2. Landpimp

    Landpimp

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    have you adjusted the rear drum brakes? sounds like they are not adjusted up to me.
     
  3. Jukelemon

    Jukelemon

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    Rear disks all around? If so, sounds like air in the line/cracked line/just plain bad line.
     
  4. Poser

    Poser Oh...Durka Durka Durka. s-Moderator Supporting Vendor

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    Welcome.

    As John suggested, make sure the rear brakes are adjusted.

    How much play is there in the pedal before the mater cylinder begins to move? If you remove the master from the booster, you will see a accutuation rod that may be adjustable, and, there is the adjustment between the pedal and the booster to look at also. What did you do to make the booster work on the older, non power brake firewall?

    I do not think that things are adjusted properly in this area....

    A 1" bore master will provide ample fluid to the brake system, provided it is acctuated properly.. ;)


    Good luck!

    -Steve
     
  5. dentedpig

    dentedpig

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    The rear brakes were adjusted yesterday, as I thought this was a possible problem. Barely made any difference in pedal feel. When the truck is not running, the pedal actuates the brakes about 5% into the pedal stroke. When the truck is running, the pedal actuates the brakes about 90% into the pedal stroke. All of the lines are fine and there are no leaks. The MC was bench bled. On top of that, I passed 1 1/2 qts. of brake fluid through from bleeding (3 times altogether). I felt this was necessary because of the crud in the brake lines. The push rod on the inside of the truck is adjusted all of the way down to accomadate the landcruiser brake pedal. On the firewall, I moved the mounting points about 1/2" to the right and about 1/4" down. To make up for this, I fabricated a different mount to mount the pushrod to the pedal. I did not notice an adjustment on the pushrod that goes between the MC and the booster. However, upon further inspection, this pushrod moves in and out freely with absolutely 0 resistance. When not connected to the MC, the booster has a "flat" spot in its travel. A point where resistance is lost and gained again. I have not yet checked the vacuum that my manifold is pulling, but will do that tommorrow. One good thing I've gained from this, I realized that 2 of my wheels are 3.75" BS while another 2 are 3.5"BS. They look identical, but I noticed that one rim required grinding of the caliper for fit, while the other did not.
     
  6. dentedpig

    dentedpig

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    All right, I'll reply to myself here since I didn't think before typing my last message. The master cylinder begins to move just as the booster push rod begins to move, there is no free play there. When not running, the brakes feel great. No double pump or anything of the sort. Now today I was inspecting it some more, and running or not, the brakes actually lock up with very little pedal travel, there just is no resistance whatsoever to provide brake modulation/control. In the older landcruisers, clearance around the booster can be a problem, mine barely fits between the throttle cable and the clutch MC. In the junkyard this morning I notice some very small boosters that had the same bolt pattern as the toyota MC. They were on very old chevy luvs/isuzus. The only problem is that the bolt pattern on the firewall doesn't match up. FYI.

    So, am I in need of a proportioning valve or something to limit the pedal travel. It seems like the front brakes grab before the rears, even though the rears are adjusted out as far as I am comfortable with.
     
  7. Jukelemon

    Jukelemon

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    I know you said you bled the system but it keeps sounding like an air pressure issue. I had a vehicle do the EXACT same thing and it was a cracked line barely noticeable. You may want to check the air inline again.