Adjusting Master Cylinder rod

Discussion in 'Classic Mustang Specific Tech' started by geostang351, May 4, 2007.

  1. geostang351

    geostang351 Member

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    How do you and how much do/can you adjust the MC rod that goes from the power brake booster to the MC? My pedal bottoms out too soon and I'm guessing I can adjust this rod so that brakes work a little sooner in their travels.
     
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  2. ForceFed70

    ForceFed70 That's why they call it "dope"
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    In my '70 the rod isn't adjustable, I don't think yours is either.

    Does the pedal bottom out shortly before it hits the floor, of 1/2 way through the stroke?


    Could your problem be related to old lines ballooning or air in the brake lines?
     
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  3. geostang351

    geostang351 Member

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    Bottoms out to the floor basically.

    I just rebled the brakes again this weekend just to make sure the air is completely out. I changed the calipers this winter so new fluid is in the lines. The rubber hoses that go into the caliper are only about 6 years old themselves.

    Why do you think it is non-adjustable? Can I put in a long rod and do you think that would help?
     
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  4. jcode68

    jcode68 Active Member

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    That is a lot of pedal travel to make up for with an adjustment to the rod. As I recall, the rod (at least in my 68) has less than an inch of adjustment and it may actually be closer to 1/2 inch. Has it been like this the whole time or did it get worse over time? Was the master cylinder bench bled before installed in the car? You could have air in the MC that will not come out in the normal brake bleeding process. Lastly, I would check the brake pedal where it connects to the booster. This rod is also adjustable in some models.
     
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  5. gsxrken

    gsxrken Member

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    There is a specification for how to check the pushrod length. PM me and I can dig it up in the 69 shop manual. But they're usually fine. I'd ask you to check the orientation of the calipers. They are RH and LH specific and often installed on the wrong side of the car. What's odd about them is that the bleeder screw should point to the rear of the car, not up. If they're on the wrong side, you will never get all the air out and you will have alow pedal.
    Of course, make sure your rear shoes are right up against the drums for a high pedal and effective e-brake, too.
     
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  6. jcode68

    jcode68 Active Member

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    That strange, everything I have read specifies the bleedera should always be pointing up, otherwise you will never get all the air out. Is this something specific to the stock 69 calipers?
     
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  7. 2nd Mustang

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    I'm going through some brake problems on my 67 coupe with power front discs. I've basically replaced everything, MC (twice), front calipers (twice), distribution block, rear cylinders, springs and shoes (Torino drum brakes), and other things.

    I've tried the specific length adjustment on my push rod as suggested by the Ford factory manual, but found that the brakes lock up too soon, and I do mean lock up, so have been adjusting the push rod to be shorter. It still locks up occasionally upon heavy braking so will adjust it even shorter next weekend.

    I noticed something weird though. If I give the pedal one light pump before before braking to a stop, the brakes don't get grabby at all. Yes, I have bled the MC and all lines.
     
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  8. geostang351

    geostang351 Member

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    I guess I'll try to adjust the rod and go from there. The calipers appear to be on the right side as the bleed screw points back up and is located at the top of caliper.

    The rod from the booster to the pedal is adjustable too? That would take work to adjust this as the assembly is together.

    The MC was never bench bled priot to installation but I've bled the brakes about 4 times im 6 years. There could still be air in there?
     
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  9. 2nd Mustang

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    Don't take this as gospel, but this last time was the only time I really bench bled the MC using lines curled back into the bowls. Prior times, I just put a lot of rags under the MC and pumped away.

    The rod from the brake pedal to the booster didn't have any adjustments on mine.

    Happy tweaking, oh what fun.
     
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  10. 2nd Mustang

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    I finally got the brakes working great. I measured the inside length of the MC where the rod would go in and in order for the rod not to be touching all the time, it required that I take out all the available adjustment on the push rod. The brake pedal still is at the same height. Funny thing, the MC I took out, required more length of the push rod when I installed it five years ago. :shrug:

    Getting back to your original question, if the pedal is going to the floor, can you pump the pedal to build pressure or some pedal height? If yes, then probably air in the system, but if no, probably if equipped with rear drums, they need to be adjusted.
     
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  11. geostang351

    geostang351 Member

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    If I pump, it still goes to the floor. The car does have rear drums? How do I make this adjustment?
     
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  12. 2nd Mustang

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    The same as adjusting using the star wheel on the inboard side of the backing plate. It will allow the shoes to be closer to the drums and also help with the length of pull on your parking brake handle.

    If you pump and it still goes to the floor, it would seem to me that you have other issues on top of the rear brake adjustment. Even with the rear brakes completely out of the picture, you should still have some braking ability on the front brakes if you have the dual reservoir.
     
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  13. geostang351

    geostang351 Member

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    I do, that is why I am asking for help
     
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  14. 2nd Mustang

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    Apparently you have brake fluid going to the front calipers if you were able to bleed them, but even with air in the lines, you should be able to build up some kind of pressure and keep the brake pedal off the floor.

    Try pumping the brake pedal while someone else tries to spin the front tires by hand to see if the tires will even try to stop. If they don't stop, then more than likely your MC isn't directing enough pressure to the calipers. I assume your calipers are new? Can you see if the caliper piston is moving while you pump on the pedal?
     
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  15. geostang351

    geostang351 Member

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    Would the proportioning valve possibly be bad? The calipers are new. I'll have to try the "rotating wheel" scenerio to make sure that the fronts work at some point.
     
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