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Thread: Brake woes...

  1. #1

    Unhappy Brake woes...

    I've done the SN85 Front spindles and brakes with rear Lincoln Mark VII disks and calipers with ranger rear axles. Installed the 95GT brake master cylinder from LMR 1 1/16", recommended for disk / disk setup. Using my original 1985 brake booster. Problem is I have bled these brakes over and over again, no air at any bleed screw. I pump up brakes, 3 quick presses, then open bleeder screw, until pedal to the floor, tighten bleeder screw then repeat. Took forever to not get any bubbles at bleeder screws. But have never had good pedal feel thorough the process. When engine off, you can pump up the brakes to get good pedal feel. With engine on, pedal goes right to the floor. Very frustrating. Here are my thoughts.....

    1) No brake fluid seeping at any junction so no air leaks.
    2) Must have air in the system or would not be spungy.
    3) Brake lines to both front passenger and rear brakes are mounted on firewall just below hood (Higher than master cylinder).
    4) Using SN95 porportioning valve with valve still in place.

    I was planning on taking the stang out for a run and start testing out the pedal travel, rear lockup, etc, to start to work out the proper portioning setup, and just wanted to be able to stop for now.

    I am wondering if I need to move the brake lines lower that the master cylinder to ensure that air cannot get trapped. Since this is the only place I can figure out where the air is hiding.... All thoughts and ideas appreciated...

    Rich
    85 GT vert with 88 drive train
    Orlando

  2. #2

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    I feel your pain, I have the same problem. Mine is to the point where the car will stop, but the proportioning is still off with the adjustable prop valve all the way open. I'll be interested to see if anyone has anything new to add here. I've tried everything.

    As for your lines under the hood running along the pinch weld, that's where the factory put them, so I can't imagine that's too much of a problem.

    You can look up my thread "Air STILL in the brake lines?!" for some ideas if you want.

    Sent from my SM-G960U using Tapatalk
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI, T-5
    '17 Ford Focus ST
    '14 Ford Fusion SE Manual

  3. #3

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    Sounds like air to me!

    First, I never, never pump the pedal before bleeding. I have someone step on it and we do the procedure, I say "down", when it hits the floor they say "down" then snug the bleeder screw. Quick pumps cause air bubbles.

    Use some teflon tape on the bleeder screws, you will get air bubbles from the thread. This isn't your problem, but it make bleeding more accurate.

    Did you pre-bleed the master? You can still do it, just get a cheap kit and bleed the master into itself until no bubble appear. Don't press fast and hard, just step down. It might take a few minutes as you need the bubbles to subside in the master after each press. You can introduce a lot of air into the system if you go "fast and hard".

    Are you sure you have the calipers on the correct side? Is the bleeder at the highest point? Just saw this on an early TBird disc conversion. The can go on either side.

    I don't believe the high lines will have any effect on your brakes.

    You must have a lot of air in the system. Be patient, you will figure it out.

    Post of picture of the brakes, maybe someone will see an issue.

    I also bleed with the adjustable proportioning valve at its highest (screwed in) setting. Not that it makes a difference as far as I know, just a habit.

    Kenny
    Last edited by mudgepondexpress; 05-26-2020 at 06:29 PM.

  4. #4

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    x2 on the air in the system and checking bleeder orientation. When I did my SN95 swap, I didn't bench bleed the master cylinder and had zero issues bleeding the system.

    Start bleeding the system at the caliper furthest from the master cylinder (right rear IIRC) go to left rear, then front right and front left. Rinse, lather, repeat as needed.

    Personally I'd also remove the SN95 proportioning valve and install an adjustable in it's place. Once this is resolved, bleed the system again and report back.
    Jeremiah

    1986 Mustang GT 5spd, 3.27's
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  5. #5

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    I agree that it feels like air still in the line....When I bleed brakes, I always start with: bleeder screw open, brake pedal slow down, when at floor "DOWN", close screw, pedal up "UP" and repeat the process until no bubbles. But this requires a partner, and I was getting restless and did not want to wait until my wife had time to give-me-a-hand, so I started with a vacuum brake bleeder system. The Teflon tape on the bleeder screw is the only way it you are vacuum bleeding or it will pull air in from the bleeder screws. Anyway did this probably 6 times around the entire car until no bubbles could be seen. Should be good right? Nay-Nay. Pedal right to the floor even with engine off. Would not even pump-up. Gave up on the vacuum bleeding and waited for wife. Finally started the buddy bleeding down-up, down-up, a little air in the rear lines, no air in the drivers front, lots of air in passenger front. Wend around car 5 times. Clear fluid finally at all wheels. Should be good right? Nay-Nay. Climbed in car slight pedal, pumped it up to firm pedal in three quick pushes. Started car, no pedal no pumping up.... Scratching head, had a beer, looked under hood and all lines for leaking joint since I thought on down pedal, it should push fluid out of a leaking joint, then up pedal could pull air into joint. No fluid anywhere...... idea did not pan out. Looked at brake lines running higher than master cylinder and thought how would air get out of those lines, since bubbles always seek the highest point, and it appears it would be trapped. Then I remembered that high enough pressure will force air into solution, and once in solution you can bleed it out with the fluid, so I started the quick down-down-down, open bleeder, down to floor - close bleeder, repeat process. The amount of air that came out of the passenger front was incredible, did this 15 times per wheel, and did 5 times around the car. Has to be rock solid now...Nay-Nay. Now have spungy brakes with car off, no brakes with car on....This is why I am seriously thinking about re-running the brake lines to make sure the master cylinder is the highest point in the system and no humps in lines where air could be caught.

  6. #6
    Moderator wraithracing's Avatar
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    Most brake suppliers don't recommend depressing the brake pedal all the way to the floor when bleeding. That can overstroke the MC which can cause damage and allow internal back bleeding in the M/C. Most recommend going to @ 2" above the floor and stopping there. Often I will place a small 2x4 flat under the brake pedal to prevent me from depressing it too far.

    My brake bleeding procedure is a bit different than some because I usually do it solo. I use a 1 quart mixing cup. Filling the bottom 1/4-1/3 with clean new brake fluid. I get the proper size vacuum line that fits the bleeder screws tightly and enough length so that I can attach the hose to the bleeder screw and the hose end will be submerged in the brake fluid. I crack open the bleeder screw 1/4-1/2 turn. Just enough for fluid to come out, but not so much that it leaks around the threads. Then I make sure the M/C is full of fluid and I stroke the brake pedal 8-10 times slowly allow it to return to the top by itself. I check my fluid in the M/C and see how much fluid has been bleed into the cup. I will generally run 8-16 oz of fluid through each bleeder screw. If using a paint mixing cup its easy to read how much. Once I am satisfied with the amount of fluid, I move to the next wheel. I start at the passenger rear wheel, the driver rear, front passenger, and end with driver front. After one full round and usually 1 to 2 bottles of fluid depending on if I am flushing or bleeding a new system the brake pedal feels very firm and all the brakes are operating. I then drive the vehicle for a week or so as is (assuming the braking capacity is good) and then I do another round of bleeding flushing 4oz-8oz per wheel again assuming the are no braking issues. This will generally give me an excellent pedal feel and no air in the system. I have done it this way for 25 years and get better results than my friends with vacuum brake bleeders. If you have a friend, buddy, etc that can pump the pedal while you watch the fluid in the cup, you can watch for bubbles to make sure you get all the air out and then quit at that point. I still bleed a second round, just because I have often gotten additional air out the second time that seems to get trapped somewhere in the lines during the first bleeding. Having the vacuum line submerged makes sure the system can't suck air back into the lines when you release the brake pedal is the reason I do it this way. The open/close of the bleeder screw works, but this is faster for me and works perfect in my experience. Good Luck!
    ​Trey

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  7. #7
    FEP Super Member gr79's Avatar
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    x2
    Asking someone to pump the brakes is more work. Communication and skill is the problem.
    Never got good results that way no matter who was helping.

    Open bleeder screw 1/3-1/2. Or minimum to allow good flow and quick close.
    Use box wrench. Or soak and socket if bleeder is real tight initially. Preserve the bleeder flats.
    Removing and taping the bleeder screw keeps air out and treads lubed.
    Push brake pedal down easy, count 1001, 1002, 1003, then let up count 1004, 1005, or even 1006.
    If not using hose-in-- fluid procedure, tighten bleeder at 1003 count. Have helper working pedal count out loud.
    With no tape and hose in fluid, harder to get and keep all the air out.

    Hose-in-fluid procedure is a continuous purge operation. No need to keep open/closing bleeder.
    Open when starting, close when satisfied all air is gone. Micro bubbles ok.
    The vinyl hose is like an extension of the brake line if set up and done right.
    Can open or close bleeder at will when tubing is immersed in fluid. Close bleeder before removing tubing.

    One quart of regular brake fluid is plenty to do many purges. Two pints should be plenty or even one if careful.
    Having extra fluid left over is ok. Quart is a better value. Stays fresh enough if recapped quickly.
    Opening then storing brake fluid is not mixing epoxy with clock ticking.

    Height of brake tubing run is not a factor as long as enough fluid is run completely thru to purge air slugs.
    20-30 pedal push cycles are no big deal. Better more pumps than not enough.
    Brake fluid is inexpensive. Good firm brakes are a safety factor. Cars/trucks/people are large investments.
    3 pedal pushes are surely not enough. Minimum of 12.
    Check master cyl resv level every 12.
    After driving, will check for leaks and rebleed only if pedal lacks normal height, feel, and action.

    DIY tool. Keeps accidental tip overs to a minimum and holds a lot of used fluid.
    Slim 12 oz+ plastic bottle in glass jar. Vinyl tubing is long and same id as bleeder screw. Can see air moving thru tubing.
    Simple components, quick bleed with consistent positive results.

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    Last edited by gr79; 05-27-2020 at 01:23 PM.

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