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brakes locking up on me

Discussion in '40- & 55-Series Tech' started by bj40man, Jan 16, 2003.

  1. bj40man

    bj40man

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    Hello fellows,

    This is my first post to the forum! :D
    I am currently working on a BJ40 that I inherited from my dad. It is a 1975 bj40 with poor country specs - which means no front disk brakes, no booster & single cylinder master brake pump (yuk!) among others. I have already replaced the factory engine with a 3BII out of a 1998 Toyota Dyna truck. This engine came with very low mileage and a few other goodies such as a power steering pump and vacuum pump incorporated on the crankcase. This forced me to install power steering and front disk brakes. I got new vented rotors for Land Cruiser and other used parts from a hilux (mini truck in USA) I also got a proportioning valve off from an old disk brake Land Cruiser. I put in a booster and a new 7/8 master cylinder brake pump same as found in a disk brake cruiser, but now when I start the engine in the morning, the brakes are way down and as I drive they kind of start coming up and eventually lock up on me. I have to bleed the line for the brakes to loosen up again. This seems to happen with regards to the rear breaks, but these also affect the front ones. &nbsp:Do you have any ideas what is bugging my cruiser? I am at a total loss. I first thought it could be the booster pushing the master cylinder, but then I took the vacuum out and ran it for a while, and still the brakes kind of charge until lock up. Any ideas are greatly welcomed.

    Thanks,
    Gustavo Lepe
    Bj40man
    Tegucigalpa, Honduras
     
  2. woody

    woody Internet Fireman Staff Member

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    Check to be sure the adjustment rod between the pedal arm and the master is adjusted properly...too long, and it will build pressure each time you hit it.
     
  3. Guest

    Guest Guest

    Just a thought, but is that master cylinder (pump) made for the disk brakes. If it is a drum brake application it will have residual pressure valves in it. This is meant to prevent too much slack building in the brake cylinders of the drums, but if used on disks will prevent them freeing up. They are basically one way valves, but there is some slow bleedback.
    Good luck
     
  4. Erics75

    Erics75

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    I agree with both Brian and Martin, push rod adjustment is important, and different m/c (master cylinders) have different depths in the m/c piston for the pushrod. The fact that it also does it w/o the brake booster would indicate that there is a check valve in the m/c but only for the rear brakes, so if you plumbed your rear brake line to the rear m/c port ( closest to firewall ) like your drum brakes were then its incorrect. The disc brakes plumb to the rear port ( closest to firewall ) and rear brakes to the port nearest the front of the vehicle. The disc brake reservior will be the largest because your calipers have no adjustment for brake wear. BTW the check valve keeps a few lbs of pressure in the brake line to prevent air from entering the wheel cylinders, the return springs on the brake shoes are applying pressure on the shoes which in turn push the w/c pistons back into the cylinders when you release the brake pedal.
    Eric
     
  5. pfry

    pfry

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    My "drum" master Cylinder was doing the same with front disks when I converted.
    Woody recommended I pull the little "residual pressure" valve out of the master cylinder. It works fine know.
    If you take off the front brake line off the master cyl. and then the fitting that is in the cyl. There is a little plastic thingy about as big around as a dime.
    Pry it out and pitch it in the trash.
    Reassemble and bleed.

    Also I've has stopped up brake hoses, the flexible at the wheels give me fits.