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  1. #1
    FEP Supporter Broncojunkie's Avatar
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    Default Need some brake help/advice

    I've been fighting with a brake problem on my pace car for a while. Since I restored the car, I went ahead and pretty much replaced everything except for the brake lines on the front half of the car and the booster. Everything else is new. After bleeding them multiple times, I still have little pressure and hardly any brakes. No air appears to be coming out when I bleed them, nothing is leaking, and wheel cylinders and calipers are brand new, along with master cylinder and all soft hoses.

    At this point, I'm suspecting that the new master cylinder is bad. Before I go replacing it, what do you guys think?

    Also, I'm planning on doing a 5-lug swap this summer. I already have an 87-93 booster and 94-95 spindles, control arms, rotors, calipers, etc. Should I go ahead and replace the booster with the larger 87-93 piece and use a newer master cylinder? If so, which MC works best with the larger front brakes? I'll be sticking with 87-93 drums for now (I'll be swapping the 7.5 rear for a fresh 8.8 very soon).
    Last edited by Broncojunkie; 04-11-2018 at 07:21 PM.

  2. #2

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    I would start by explaining the symptoms. Saying that "I have very little pressure" is a diagnosis.

    When you press on the brake pedal, how stiff is it? How hard are you pressing? How far does it travel when pressed this hard?

    What is the behavior of the brake pedal after the engine has been shut off and the brake pedal has been depressed and released 10 times?

    Have you put a vacuum pump and/or gauge on the brake booster to see if it is holding vacuum and/or measure the engines vacuum level at idle?

    Have you bed the brake pads into the rotors? What does the friction surface of the rotors look like?
    Jack Hidley
    Maximum Motorsports Tech Support

  3. #3
    FEP Supporter Broncojunkie's Avatar
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    The pedal is soft and will go all the way to the floor, with very little pressure. As far as the rotor surfaces, there is barely any noticeable wear. The car has only been moved around the driveway a couple times. Vacuum pressure isn't great, but I think a bad booster would result in a hard pedal... unless I'm missing something.

  4. #4
    FEP Supporter Broncojunkie's Avatar
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    Oh, and about the vacuum pressure, it's not great because of the cam, I believe. I'm only showing around 10 lbs at idle (quite a bit more with any throttle). I also just realized today that my vacuum gauge is crap, so I need to double check that reading.

  5. #5

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    If the brake pedal is that soft, then there is air in the system.

    When you start the engine, the vacuum booster can start to apply assist, so if it is working correctly, the brake pedal will move more with the same applied force due to the assist from the booster. If the booster were broken, it would either leak air into it and make noise (also with a high engine idle) or the brake pedal stiffness would be the same with the engine on or off. 10in of vacuum is not very much, but that isn't your first problem.

    Bench bleed the m/c with it mounted on the car and the brake lines attached. There is probably air in it. Until that air is removed, it is impossible to bleed the rest of the system. Bench bleed the m/c, by holding the brake pedal down, turn one of the nuts CCW on the outlet brake line 1/4 turn. Once the brake pedal goes to the floor, close the nut and release the brake pedal. Hold a pile of rags below the nut to keep brake fluid from going everywhere. Repeat this procedure for both outlets three or four times. Once this is done proceed the bleed the rest of the system normally at the calipers and drum cylinders.

    This should make the pedal firm and then you can test the brakes to see if there is enough vacuum from the engine.
    Jack Hidley
    Maximum Motorsports Tech Support

  6. #6

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    Verify the master cyl is good.

  7. #7
    FEP Supporter Broncojunkie's Avatar
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    Quote Originally Posted by Jack Hidley View Post
    If the brake pedal is that soft, then there is air in the system.
    I really don't believe there is. I bled the mc before attaching the lines, using the kit that came with it. Remaining lines have been bled multiple times and literally pumped a few bottles of fresh fluid through it. I tried bleeding the system again last night and not one bubble came through. My thought is that the new mc is bad, but I'm not sure how to tell for sure, other than just replace it. Thoughts?

  8. #8

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    If there is no air in the system, the only other possible source of a soft brake pedal is incorrect adjustment of the drums. The adjuster wheel in the back should be turned so that you can just barely get the drums back on over the shoes. If that isn't the problem, I can almost guarantee that the problem is from air in the system. It could be a defective, brand new m/c, but the odds of that are 0.01%. The m/c has to fail in a very specific way for it to not push fluid, but for the fluid to not come out the back of it and onto the front of the vacuum booster.
    Jack Hidley
    Maximum Motorsports Tech Support

  9. #9
    FEP Supporter Broncojunkie's Avatar
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    Quote Originally Posted by Jack Hidley View Post
    If there is no air in the system, the only other possible source of a soft brake pedal is incorrect adjustment of the drums. The adjuster wheel in the back should be turned so that you can just barely get the drums back on over the shoes. If that isn't the problem, I can almost guarantee that the problem is from air in the system. It could be a defective, brand new m/c, but the odds of that are 0.01%. The m/c has to fail in a very specific way for it to not push fluid, but for the fluid to not come out the back of it and onto the front of the vacuum booster.
    Rear brakes are adjusted properly. I also pulled drums the other day just to make sure. I'll try the master cylinder bleed again and see what happens. Thanks for the help!

  10. #10

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    Sure sounds like air in the system to me. Bleeding the new master cylinder I installed a few years ago was quite an ordeal to bleed manually on the floor until all of the air was out of it, and then installed it, and bled each wheel, and no issue. Dunno what "kit" you mean came with it for bleeding, but it doesn't sound like it works very well.
    Mike
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  11. #11
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    Quote Originally Posted by Walking-Tall View Post
    Dunno what "kit" you mean came with it for bleeding, but it doesn't sound like it works very well.
    Most rebuilt/new master cylinders I have seen come with two plastic fittings to thread into the outlet ports of the m/c. Then they give you a couple of short lengths of hose that install onto the plastic fittings to route back into the fluid reservoir. Kind of like this, but just with the parts you need. https://www.amazon.com/Dorman-13911-...er+bleeder+kit
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  12. #12
    FEP Supporter Broncojunkie's Avatar
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    Quote Originally Posted by KevinVarnes View Post
    Most rebuilt/new master cylinders I have seen come with two plastic fittings to thread into the outlet ports of the m/c. Then they give you a couple of short lengths of hose that install onto the plastic fittings to route back into the fluid reservoir. Kind of like this, but just with the parts you need. https://www.amazon.com/Dorman-13911-...er+bleeder+kit
    Correct. The last few master cylinders I bought came with the bleeder kit.

  13. #13

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    With some m/c it is very difficult to stroke both pistons 100% with the m/c in your hands. It is much better to bleed the m/c when it is installed in the car and held level. This guarantees that it is done correctly.
    Jack Hidley
    Maximum Motorsports Tech Support

  14. #14
    FEP Supporter Broncojunkie's Avatar
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    I was called back to work for a couple weeks and wasn't able to do much to the car till today. I got me a master cylinder bleeder kit as suggested and bled it on the car. I also found my Mighty Vac bleeder and bled each wheel. It didn't change a thing. Brakes still suck. I'm 99.999% certain that this new master cylinder is garbage.

  15. #15
    FEP Supporter Broncojunkie's Avatar
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    Well, I slapped a new (reman) master cylinder on it and now have brakes! I still need to bleed the system at the wheels, since I only bench bled the mc and threw it on. But it's a night and day difference. Now, I just need to figure out my timing/carb issues.

  16. #16

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    For the 5 lug swap...are you planning on just running V6/Gt rotors and calipers? I have a 95 MC, clean single piston calipers with new ceramic pads, new drilled rotors and new 5 lug drums from LMR. Not using any of it since I went with cobra setup and disc in rear. Let me know man

  17. #17
    FEP Supporter Broncojunkie's Avatar
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    Quote Originally Posted by T-O-N-Y View Post
    For the 5 lug swap...are you planning on just running V6/Gt rotors and calipers? I have a 95 MC, clean single piston calipers with new ceramic pads, new drilled rotors and new 5 lug drums from LMR. Not using any of it since I went with cobra setup and disc in rear. Let me know man
    I have pretty much everything already, but I did pm you with some questions.

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