push rod adjustments - disc brakes

Discussion in '40- & 55-Series Tech' started by brooklyn, Sep 6, 2010.

  1. brooklyn

    brooklyn SILVER Star

    Messages:
    423
    Fj04
    Disc Brakes (front & rear)
    Problem: Brakes grabbing after 20 minutes of driving.
    Suggested 1h8mud solution: Adjust the push rod

    Followed the advice of a few fellow posters and added shims between the master cylinder and brake booster and then test drove.

    1st shims - 4mm
    2nd set - 2mm
    3rd set - 1mm

    In all cases the binding brake problem was solved and no more mad hot rear calipers and dragging brakes.

    ONE LAST ISSUE - the brake pedal does not fully return and this keeps the brake light on an may be slightly applying the brakes.

    I have a return spring and I can hook my foot under the pedal an it returns easily, but no so easy that the spring works.

    There is a slight groan when I come off the brakes on a hill right before the truck rolls.

    Some pictures are included - this one has the 4mm shims

    Any ideas??????
    4mm.jpg
  2. fieldsken1

    fieldsken1 SILVER Star

    Messages:
    2,480
    Location:
    in my little world
    maybe its rubbing on the shims.
  3. brooklyn

    brooklyn SILVER Star

    Messages:
    423
    shims (2mm and 1mm)

    Here are pics of the 2mm and 1mm shims I used. The best braking performance seemed to come when I was using the 1mm shims.

    However, the brake light stayed on and the brakes pedal needed to be pulled up using my foot.

    Shortened the return spring, but still could return the pedal to the top.
    1mm.jpg
  4. brooklyn

    brooklyn SILVER Star

    Messages:
    423
    prop valve

    Here is a look at some of the plumbing....
    IMG_5381.jpg
  5. Ray185

    Ray185

    Messages:
    12
    Location:
    Australia
    Can I ask why you are adjusting pushrod to master clearance by adding shims rather than just adjusting the pushrod itself (you know it is adjustable right?)?
  6. brooklyn

    brooklyn SILVER Star

    Messages:
    423
    Using an 8" power booster

    Using an 8" power brake booster and the matching master cylinder.

    Here is what I have as possible next steps


    1. replace rubber brake lines - previous owner mentioned having some issue bleeding one of the rear lines - didn't get good flow. Didn't pay much attention at the time, but maybe this is an issue.

    2. swap out the booster & master to see if that is the issue

    Any other ideas on why this may be occurring????
  7. fieldsken1

    fieldsken1 SILVER Star

    Messages:
    2,480
    Location:
    in my little world
    thats what i was wondering also. the little rod the comes from the booster and pushes on the master can be filed down as to not have any pressure on it also you can adjust the push rod from the pedal to the booster to fix the amount of play. as far as the brake light staying on why cant you adjust the switch?
  8. brooklyn

    brooklyn SILVER Star

    Messages:
    423
    Using Shims

    Yes, but I didn't want to disconnect the brake lines from the master cylinder every time I made an adjustment. The lines are too short to just move the master cylinder aside.

    Adjustment is done from the MC side of the booster unless I misread the instructions.
  9. Ray185

    Ray185

    Messages:
    12
    Location:
    Australia
    Normally, for stock landcruiser master and booster setups the little pushrod inside the booster that pushes the master cyl on pedal application is adjustable (two pieces, threaded with two 8mm hex heads for adjustment). It does not need to be filed down. Winding the rod in and out is easily done with two 8mm spanners. You don't need to move the master cyl very far to get the rod out, maybe an inch or so at most. Your master cyl brake pipes will flex enough for this.

    It sounds like your push rod is set too long and is pre engaging your master cyl with no pedal effort. You need to shorten it. Remove the rod after moving the master back enough to do so. Mark a line (permanent marker/scribe/etc) across the rod so you have a reference of where the adjustment was. Wind the rod in with your spanners and put a small dab of grease on the end of the rod (master cyl end). Put the rod back in and bolt up your master cyl. Remove the rod once again and see if the grease on the end has deformed indicating that it has engaged the master cyl piston. If it has, wind it in a touch more and repeat. You want there to be about 1mm clearance between rod and piston so it will take a little fine tuning. Try and adjust the rod in quarter turns each time. This "should" fix your problem. Again this is based on stock toyota master/booster setups. I don't recognise that booster/master you are using (I'm an Aussie) so the pushrod may not be adjustable in exactly the same way I have described but should still be adjustable.

    Good luck.
  10. fieldsken1

    fieldsken1 SILVER Star

    Messages:
    2,480
    Location:
    in my little world

    if you look i dont think it is a stock mc/booster
  11. mattcamp

    mattcamp

    Messages:
    750
    Location:
    Aloha Oregon
    You need to replace the return spring with one that brings the pedal all the way back up(away from the floor) if your foot is not pressing the pedal it should never sag down towards the floor, that would explain your brakes engaging and getting hot, also the groaning as you start to roll down the hill, the wieght of the pedal if it is sagging down is enough to slightly engage the brakes, if you drive like that it will get the brakes smoking hot from the friction and cause premature failure.

  12. Ray185

    Ray185

    Messages:
    12
    Location:
    Australia
    Yep, doesn't look stock to me either by Australian standards, I figured your (US delivered) 40s might be different to ours in this area...and by different I mean ass backwards. :hillbilly:
  13. fieldsken1

    fieldsken1 SILVER Star

    Messages:
    2,480
    Location:
    in my little world

    i dont have a return spring on mine and it works fine some did not have that. however a stiffer spring would not hurt
  14. bsmith123

    bsmith123

    Messages:
    3,079
    Location:
    Norfolk United Kingdom
    Sounds like the answer is more adjusting


    Brakes
    NOTE: Correct push rod length is essential to reliable braking. If the rod is too long, it causes the compensating ports in the master cylinder to be closed off, eventually resulting in brake drag. If the push rod is too short there will be excessive brake pedal travel and possibly there will be a groaning noise ;) from the brake booster. Use the following procedure to check the push rod adjustment.
    CAUTION: Wear protective goggles when performing the following procedure! Brake fluid may erupt from the master cylinder with sufficient force to cause personal injury.
    1. Remove the master cylinder reservoir cap or cover.
    2. While an assistant slightly depresses the brake pedal, watch for fluid to erupt in the reservoir when the pedal is depressed 3/8" to 1/2". This indicates correct push rod length. On dual system master cylinder, fluid may spurt only from the front reservoir.
    3. If the pedal travels more that 1/2" before master cylinder fluid erupts, the push rod is too short. If nothing happens no matter how far the pedal is depressed, the push rod is probably too long. 4. To adjust the push rod length, first remove the master cylinder from the power booster. Using a pair of pliers, turn the push rod adjusting nut in to shorten and out to lengthen the push rod.
    5. If the push rod is non-adjustable, use shims between the master cylinder and power booster to shorten it. If too short, remove existing shims or remove the push rod from the booster and replace it with one of the proper length.
    6. Install the master cylinder onto the power booster and recheck push rod length. 7. Connect the vacuum hose(s) to the power booster.
    8. Reconnect the ground cable to the battery.
    9. Make sure the braking system works correctly before moving the vehicle. If the pedal is soft or has excessive travel, it may be necessary to bleed the entire braking system.
    930393h.jpg
  15. cmiller114

    cmiller114

    Messages:
    298
    Location:
    Enola, PA.
    There is a simple "H" shaped tool that makes this job quick and easy.

    SPX Toyota | Tool Detail

    Easy tool to make as well.

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