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Technical Brake Bleeding!?

Discussion in 'The Hokey Ass Message Board' started by jaw22w, Jan 2, 2022.

  1. jaw22w
    Joined: Mar 2, 2013
    Posts: 1,407

    jaw22w
    Member
    from Indiana

    I am embarrassed to post this. Very rudimentary. I have never been able to get the kind of brake performance that I know my brakes were capable of. I started out with the GM metric calipers and Corvette master cylinder. I couldn't get them bled out to my satisfaction. Always took a pump to have good brakes. I'll bet over the 3 years I played with that system I ran 5 gallons of fluid through it trying to bleed it out. It got really tiresome. I figured it had to be trying to build a system with mis-matched parts. So with all the "stimulus" money still burning a hole in my pocket I installed a complete new Wilwood disc brake system. D154 calipers front and rear, 7/8" master cylinder, proportioning valve, residual pressure valves and braided flex lines. I cannot get the air out of the system! First hit of the brakes gives just barely adequate braking. One pump then gives great braking. First hit goes a long way down, second pump gives a high hard pedal. So it's not a lot of air, but there is some there. There are no leaks. Annoying as hell.
    My very first attempt at bleeding the system was using my vacuum pump. That got it close, but not 2 pump close. So I got the wife out to do the pump, hold and release method. That got me to where the second pump gave me good brakes. Driveable but not good. So, then I tried the hose in a bottle with some fluid in it. I pumped a quart through each caliper. Still a 2 pump system. I have re-bench bled the MC a couple of times. I have been taking the calipers off and using spacers to mock the rotor because as mounted the bleeders are not exactly at the top. The bleeders are not far from being straight on top, but I have been removing them to get that last little bit of air. I have tried bleeding the rears with the proportioning valve both ways. I have checked each line individually for flow. Unfortunately nothing has got that last little bit of air out. I certainly don't have the braking performance this system is capable of. I am out of things to try and out of ideas. I know that Wilwood has engineered this whole system to work together, but I can't make it work. Just shoving more brake fluid through it ain't working.
    This ain't my first rodeo. Been playing this game for more than 50 years. Never had a system I couldn't get bled out.
    I haven't tried pressure bleeding. Never needed to. Also don't have a pressure bleeder. I have been thinking about drilling a hole in the MC cover and pressurizing the MC to force fluid in instead of sucking it in. That seems a little radical to me though.
    I would appreciate any insight any of you guys might have!
     
  2. Casey Riley
    Joined: Jun 27, 2018
    Posts: 535

    Casey Riley
    Member
    from Minnesota

    I think you could have leak somewhere that is not obvious.
     
    oldiron 440 and jaw22w like this.
  3. Are you sure that none of the rotors Are warped?
    When you Are driving along, does the discs push the brakepads and the pistons on the calippers inwards? I heard about this problem on a rally car once, it turned out to be bent axles in the rear axle

    Rune Waltoft from Norway
     
  4. 1971BB427
    Joined: Mar 6, 2010
    Posts: 7,090

    1971BB427
    Member
    from Oregon

    I think you need to be sure there's no air trapped at the outlets of the master cylinder. Even after bench bleeding the master, and then pressure or vacuum bleeding the lines, you can still have air trapped at the outlet fittings of the master cylinder output fittings.
    Get someone to help by pumping and holding the pedal down, and then break an output line loose. Repeat on the 2nd output fitting until you only get fluid at both. I've had the exact same issues you described, and both times it was air trapped at the outlet fittings that was cured once I broke them loose under pressure.
     
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  5. shorrock
    Joined: Oct 23, 2020
    Posts: 36

    shorrock

    I don´t know your Wilwood calipers but anyway, here is my solution, proven several times on my motorcycles. Exactly the same behaviour as your brakes, pedal or lever quite soft, second stroke improves the feel and braking a lot. Everytime I have this, I take the calipers into pieces and clear the recessed groves for the rubber seals, works every time!
    The reason is this:
    When the seals are compressed a bit by the corrosion or dirt behind, the friction on the piston increases. Piston will only slide through the seal when a longer travel distance is possible. This does not happen in your caliper so the seal gets deformed a bit more when brake is applied. As the deformed seal is all what pulls the piston back, you need more fluid next time as your seal pulls the piston further back than needed.
    I would clean the groves for those quad seals and use new seals. The piston should be a moveable by the palm of your hand - if not, it will give you problems like you have.
     
    jaw22w likes this.
  6. This could be as simple as placement of pushrod from pivot bolt to pedal pad relations.
     
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  7. jaw22w
    Joined: Mar 2, 2013
    Posts: 1,407

    jaw22w
    Member
    from Indiana

    This could be it. After bench bleeding I always loose some fluid out the outlet ports before I can get the lines hooked up. I have always wondered about that but never had a problem with it. It is definitely worth a try! I have it up in the air now ready to try bleeding again as soon as I can get the wife out to run the pedal.
     
  8. V8 Bob
    Joined: Feb 6, 2007
    Posts: 2,787

    V8 Bob
    ALLIANCE MEMBER

    Pressure bleeding imo is is the best method, based on many years of building/modifying/testing brake systems. It doesn't require a lot of pressure (I use 5-10psi max to keep from blowing off or damaging non-metal reservoirs) but I would use a cap and gasket designed for pressure vs trying to use a modified stock M/C cap. You want fluid volume to capture the air, not pressure. This also negates the need for "bench" bleeding.
    I also use (and recommend) a bladder pressure bleeder vs a cheap garden sprayer, to keep air out of the new fresh fluid.
    With pressure applied, you want to slowly full stroke the pedal as you bleed each brake, until no air is present, usually two or three bleeds.
    Note-the pedal travel has to be able to full stroke the master or you will not get a good bleed. A simple check is to open both systems and verify the pedal can bottom the M/C pistons before the pedal bottoms out.
    Use isopropyl or denatured alcohol to clean up connections, fittings and spills. Now test for leaks by applying very heavy pedal force.
     
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  9. jaw22w
    Joined: Mar 2, 2013
    Posts: 1,407

    jaw22w
    Member
    from Indiana

    Nope. not losing any fluid.
     
  10. jaw22w
    Joined: Mar 2, 2013
    Posts: 1,407

    jaw22w
    Member
    from Indiana

    Calipers are brand new. Clean as a whistle. Pistons move easily by hand.
     
  11. jaw22w
    Joined: Mar 2, 2013
    Posts: 1,407

    jaw22w
    Member
    from Indiana

    Pedal ratio is 5-1/2 to 1. (11-1/2" pad to pivot and 2" pushrod to pivot)
     
  12. BamaMav
    Joined: Jun 19, 2011
    Posts: 5,188

    BamaMav
    Member
    from Berry, AL

    How do your lines go through the frame rails? I have read the common "through the rail" fittings are larger than the lines and will hold air that is hard to bleed out. After I read this, when I built my system I just put my lines above the rails in the stock locating tabs. I never have any problem bleeding them.
     
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  13. jaw22w
    Joined: Mar 2, 2013
    Posts: 1,407

    jaw22w
    Member
    from Indiana

    I'll have to check into a pressure bleeder. That Wilwood MC is an 8"x3" oval. Will a pressure bleeder hook up to that?
    I think you may have hit on something I have been overlooking! When I built this car I had a different style MC in it. Before I ever got it on the road I changed the MC to a different style. I was aware that it has to have full stroke and it did have with the first MC, but it is entirely possible that it doesn't have now. My pedal has an adjustable up stop and I just set up the new MC at the same point. Could very well be short.
    So now I have a couple things to check on as soon as the wife gets out here.
    Thanks guys!
     
  14. jaw22w
    Joined: Mar 2, 2013
    Posts: 1,407

    jaw22w
    Member
    from Indiana

    I have those through the rail fittings on my roadster and have never had a problem, but I have heard those stories too. My coupe, the car we are talking about, has the brake lines run under the frame rails. So no problem there.
     
  15. lostviking
    Joined: Dec 23, 2019
    Posts: 48

    lostviking

    At the risk of sounding stupid, I've always thought that air in the lines gives a spongy pedal. Yours having a firm pedal on the second pump doesn't sound like air being compressed. Is it possible that the master cylinder doesn't push enough fluid to move the pucks in the calipers far enough? Size mismatch?
     
  16. oldiron 440
    Joined: Dec 12, 2018
    Posts: 2,526

    oldiron 440
    Member

    I've just got a question , were the lines and fittings new the first time?
    The reason I ask is I've been getting fittings that no matter how tight you make them they leak ever so little. It's totally frustrating and made me pull apart lines and start over a few times.
     
    alanp561 likes this.
  17. V8 Bob
    Joined: Feb 6, 2007
    Posts: 2,787

    V8 Bob
    ALLIANCE MEMBER

    Most pressure bleeders come with a universal cover that will work with older style one-piece masters. It's just a large rectangular alloy plate with a slotted gasket, to fill both reservoirs, and is held in place with either a large C clamp or small chains run under the master.
     
  18. jaracer
    Joined: Oct 4, 2008
    Posts: 1,307

    jaracer
    Member

    Based on the fact that you have good brakes on the second pump, I believe the problem to be the relationship between the pedal ratio and the master cylinder size. It appears that you aren't moving enough fluid on the initial stroke. I think a larger bore master cylinder would improve your problem immensely. However, it will require more pedal pressure to get the same braking effect.

    One year I decided to improve the brakes on my first sprint car by going to a smaller bore master cylinder. The brakes were much better but you had to pump them once to get a high hard pedal. I put the old master cylinder back in.
     
  19. kabinenroller
    Joined: Jan 26, 2012
    Posts: 737

    kabinenroller
    Member

    Last edited: Jan 2, 2022
    oldtom69 likes this.
  20. jaw22w
    Joined: Mar 2, 2013
    Posts: 1,407

    jaw22w
    Member
    from Indiana

    Yeah, a 6:1 pedal ratio is recommended for manual disk brakes. Mine at 5-1/2:1 should be close enough.
    As an old racer myself, I am aware of the effect of different bore MCs. I had been running a 1" bore MC before the Wilwood 7/8". It was higher but took more pressure. The Wilwood tech said either a 7/8" or 1" bore would work according to my taste for pedal effort. I like the reduced pedal effort of the 7/8" MC. The throw is still livable. I don't think that is the problem.
    I'm kind of betting on air at the MC outlet, or not getting full stroke.
    I think my wife must be asleep!
     
  21. Boneyard51
    Joined: Dec 10, 2017
    Posts: 5,351

    Boneyard51
    Member

    Every time I had a problem with a brake system that you had to give it two pumps, but then hit a solid pedal, was brake shoe adjustment. Less of a factor on disc brakes. Do you have rear drums?






    Bones
     
  22. KenC
    Joined: Sep 14, 2006
    Posts: 664

    KenC
    Member

     
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  23. jaw22w
    Joined: Mar 2, 2013
    Posts: 1,407

    jaw22w
    Member
    from Indiana

    I have spent some time researching pressure bleeders. It does not appear as though any of the available bleeders has an adapter that will fit this Wilwood MC. I would have to fab up my own adapter. The Wilwood MC cover is only a 3/16" thick flat plate held on with 4 screws. I can make a new cover plate and gasket pretty easily. The MC has a divider wall between the front and back reservoirs. It is level with the perimeter walls that the cover rests on and seals against. This divider all has an approximately 3/32" hole in it about an inch from the bottom. So essentially the front and rear brakes work off the fluid in both reservoirs until the fluid level goes below the hole joining the 2 reservoirs. I'm trying to wrap my head around where to put the pressure feed from the bleeder into the MC cover. Do I need an inlet for each reservoir?
    The Wilwood MC has a rubber bellows type rubber gasket under the cover. This gasket seals the tops of the 2 reservoirs from each other, separating them except for the 3/32" hole in the dividing wall. I could make a seal gasket that only covers the perimeter and not the dividing wall. This would leave a gap above the wall and equalize the pressure in both reservoirs. I have never worked with a pressure bleeders before and not really sure how to proceed. If I get this figured out I will order a new pressure bleeder. Am I overthinking this?
     
  24. GordonC
    Joined: Mar 6, 2006
    Posts: 2,543

    GordonC
    ALLIANCE MEMBER

    I see a lot of good ideas here but this sticks in my mind. If after pumping the pedal you get a firm pedal doesn't that indicate you are not moving enough fluid on the initial stroke. Could this be as simple as the length of the pushrod? It seems to me that is about the only thing not mentioned at this point.
     
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  25. TA DAD
    Joined: Mar 2, 2014
    Posts: 534

    TA DAD
    Member
    from NC

    It was asked earlier and I might have missed the answer, is this 4 wheel disc, or drums on the rear? If rear disc' do the calipers have manual parking brakes where the pistons screw in and out ?
     
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  26. In ages past; we sometimes had to lift either the front or rear of a truck to get it to bleed nice.

    I am sure you checked this; but be sure you are able to stroke the master fully.
     
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  27. This has been brought up a few times. He related to pedal ratio in answer to it. If you have a solid pedal after 2 strokes and it holds with foot on pressure then you don't have air in the lines, you have a volume feed issue. Air in the lines even after a second pump will give you a spongy feeling pedal. If it's firm,, no air!
     
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  28. squirrel
    Joined: Sep 23, 2004
    Posts: 50,216

    squirrel
    Member

    This will be interesting to see what the result is.

    I'm still waiting for the answer on the rear brake adjustment...that's what gave me trouble on the last one I did. Although it was drums all around, and the fronts were out of adjustment, making it seem like they needed to be bled more, and my wife was tired of all this nonsense.
     
  29. HotRod33
    Joined: Oct 5, 2008
    Posts: 2,515

    HotRod33
    Member

    Sounds like you answered part of your problem.... Pedal was higher with a 1 inch bore MC.... Does it have rear disc or drum's....? If it's drums are the shoes adjusted out enough
     
    Boneyard51 likes this.
  30. GordonC
    Joined: Mar 6, 2006
    Posts: 2,543

    GordonC
    ALLIANCE MEMBER

    Pist I saw the conversation about the pedal ratio and a 2 inch pushrod. My question is is that long enough o get the job done in one stroke?
     
    Pist-n-Broke likes this.

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