Forte's

Visit our community sponsor

Thanks Thanks:  0
Likes Likes:  0
Results 1 to 11 of 11

Thread: Pressure Bleeding Problem

  1. #1
    Member
    Join Date
    May 2018
    Posts
    89
    Post Thanks / Like

    Pressure Bleeding Problem

    We ran into a problem pressure bleeding the brake system yesterday. I have the CNC reservoir with the pressure bleeding cap. Fill the reservoir with fluid, pressurize it with a bike pump, open the bleeders until clear fluid, no bubbles is coming out. Close the bleeders and the pedal is really solid. All good so far. Then released the pressure from the reservoir, and the pedal is really soft and goes all the way to the floor. Still plenty of fluid in the reservoir at this point. We sent a pretty good amount of fluid through the system so I have to think we got the air out. Any ideas as to what might be causing this?

  2. #2
    Papa's Avatar
    Join Date
    Dec 2016
    Location
    Parker, CO
    Posts
    5,594
    Post Thanks / Like
    Did you bench bleed the master cylinders?
    My Build Thread: http://thefactoryfiveforum.com/showt...ter-Build-9754
    (Most viewed Roadster build thread on this forum!)

    Delivered: 6/17/2017
    First Start: 12/30/2017
    Completed: 12/7/2019
    Legal: 1/30/2020

    Member of the Mile-Hi Cobra Club
    Dave's Cobra YouTube Channel: https://www.youtube.com/channel/UCbk...npK1UZHj4R-bYQ
    Agora 1:8 Scale Cobra Build: https://thefactoryfiveforum.com/show...l-Build-Thread

  3. #3
    Seasoned Citizen NAZ's Avatar
    Join Date
    Feb 2016
    Location
    "The High Country", beautiful Flagstaff, AZ
    Posts
    2,443
    Post Thanks / Like
    First the basics:
    Ensure the M/Cs return all the way to the stop so that the vent port is uncovered and that the bottom of your reservoirs are above the M/C feed ports. And of course, the hoses coupling the reservoirs and the M/Cs should not be higher than the bottom of the reservoirs -- the fluid doesn't run uphill very well unless under pressure. The reservoirs must be vented to atmosphere but that vent should have an elastomeric diaphragm between atmosphere and the fluid to prevent the fluid from absorbing water from the air.
    Dart Little M 406" SBC 800 HP N/A & 1,100 HP on nitrous, 2-spd Powerglide with trans brake, 6,000 RPM stall converter, narrowed Moser 88 3.90:1 spool with 35-spline gun-drilled axles & Torino bearings, custom parallel four-link, custom tube chassis & roll cage NHRA certified for 8.5-sec (only two FFR Hot Rods have this cert).

    33 Hot Rod Super Pro Drag Racer Build: 33 HR NHRA Cert Roll Cage Build

  4. #4
    Senior Member Avalanche325's Avatar
    Join Date
    Nov 2011
    Location
    Jax Beach, FL
    Posts
    2,103
    Post Thanks / Like
    Does your pump stay attached to the cap? If not, there is hardly any air volume.

    If you didn't bench bleed, the Wilwood M/Cs do seem to bleed OK in the car. I just did a hydraulic clutch upgrade and didn't bench bleed because it was a completed car. I had to pump the pedal a bit, but it wasn't too bad. To get the M/C to fill, I find that partial 1/4 - 1/2 strokes work better than going the floor.

  5. #5
    Papa's Avatar
    Join Date
    Dec 2016
    Location
    Parker, CO
    Posts
    5,594
    Post Thanks / Like
    When I say bench bleed, I mean in the car. Just disconnect the outputs from the master cylinders and connect short pieces of tubing that run from those outputs and dump into the reservoir. Fill the reservoir with fluid and pump the brake pedal until it's flowing all fluid, no air bubbles. Reconnect the brake lines and then pressure bleed the lines and calipers.
    My Build Thread: http://thefactoryfiveforum.com/showt...ter-Build-9754
    (Most viewed Roadster build thread on this forum!)

    Delivered: 6/17/2017
    First Start: 12/30/2017
    Completed: 12/7/2019
    Legal: 1/30/2020

    Member of the Mile-Hi Cobra Club
    Dave's Cobra YouTube Channel: https://www.youtube.com/channel/UCbk...npK1UZHj4R-bYQ
    Agora 1:8 Scale Cobra Build: https://thefactoryfiveforum.com/show...l-Build-Thread

  6. #6
    Member
    Join Date
    May 2018
    Posts
    89
    Post Thanks / Like
    Thanks for the input.

    Papa- I did not bench bleed, I'll give that a try as you suggest.

    NAZ- I'll check those points too, but I do think we have the reservoir as the highest point in the system.

    Avalanche- pump stays connected to the cap during the process, there is an audible hiss of the pressure being released when you unscrew the cap. I might try your method of 1/4 to 1/2 pumps to see if we can get the MC filled before I pull off the output lines to follow Papa's method. Should we have a bleeder valve open during the pumps or have the system totally closed? I'm thinking we would need to have something open to allow for flow into the system

  7. #7
    Senior Member edwardb's Avatar
    Join Date
    Feb 2011
    Location
    Lake Orion, Michigan
    Posts
    10,547
    Post Thanks / Like
    I've used the CNC pressure cap method on four builds and it hasn't let me down yet. Full disclosure, my Coupe build has Tilton reservoirs. So bought a spare Tilton cap and put a Schrader valve on it mimicking the CNC cap. Also worked fine. My process is I bench bleed the masters exactly as Papa described. Once that's done, fill the reservoir leaving some airspace. Then pressurize. I use my compressor with the regulator turned way down. To 5 PSI or so. A bicycle pump should be the same. I guess it doesn't hurt to leave the attached. But not necessary for me because I use a tire air chuck. The cap shouldn't be leaking, e.g. hissing as described. Figure out why and fix it. Agree the pressure will be used up pretty quickly, especially the first time through when getting all the air out. But no big deal. Just hit it with some air pressure a couple times max on each caliper. Never pump the pedal during the process. Once you start, save the pedal press until you're done to confirm a hard pedal. With pressure in the system, pushing the pedal could damage seals. The one thing I see missing from all the descriptions is the order you bleed is important. Always the farthest first, then in descending order. So right rear, left rear, right front, left front. No reason to open the bleeder until you're at the caliper. I put a clear plastic tube on the bleeder and have the end in a small jar with some fluid. Open the bleeder and run until bubbles stop. May be necessary to close the bleeder, re-pressurize, and go again. Even a couple times the first time through. Make sure the bleeder is at the top of the caliper, and if using Wilwoods where they sometimes have two, always the top one. I go all around in the order mentioned. Once done, then around a second time. Usually this just confirms there are no more bubbles. But just to be sure. This process has always resulted in a hard pedal for me. I've found the process also works fine for a hydraulic clutch.
    Last edited by edwardb; 08-12-2019 at 09:06 PM.
    Build 1: Mk3 Roadster #5125. Sold 11/08/2014. Build 2: Mk4 Roadster #7750. Sold 04/10/2017. Build Thread
    Build 3: Mk4 Roadster 20th Anniversary #8674. Sold 09/07/2020. Build Thread and Video. Build 4: Gen 3 Type 65 Coupe #59. Gen 3 Coyote. Legal 03/04/2020. Build Thread and Video
    Build 5: 35 Hot Rod Truck #138. LS3 and 4L65E auto. Rcvd 01/05/2021. Legal 04/20/2023. Build Thread. Sold 11/9/2023.

  8. #8
    Senior Member CraigS's Avatar
    Join Date
    Feb 2011
    Location
    Blacksburg, Va
    Posts
    4,707
    Post Thanks / Like
    I have CNC MCs. When I was talking to them they gave me two warnings. 1- use a max of 5#. This could be a problem for you. Since there is just a tiny bit of air above the fluid in the MC, I suspect that you are way over the 5# max. 2- never move the brake pedal w/ the pressure on. I am not sure of the reason for this but they were adamant.
    FFR MkII, 408W, Tremec TKO 500, 2015 IRS, DA QA1s, Forte front bar, APE hardtop.

  9. #9
    Senior Member rich grsc's Avatar
    Join Date
    Feb 2011
    Location
    O'Fallon, MO
    Posts
    3,069
    Post Thanks / Like
    Quote Originally Posted by chjort View Post
    We ran into a problem pressure bleeding the brake system yesterday. I have the CNC reservoir with the pressure bleeding cap. Fill the reservoir with fluid, pressurize it with a bike pump, open the bleeders until clear fluid, no bubbles is coming out. Close the bleeders and the pedal is really solid. All good so far. Then released the pressure from the reservoir, and the pedal is really soft and goes all the way to the floor. Still plenty of fluid in the reservoir at this point. We sent a pretty good amount of fluid through the system so I have to think we got the air out. Any ideas as to what might be causing this?
    You should not press the pedal with pressure applied, the air pressure can prevent the piston from returning, or even force fluid behind the piston.

  10. #10
    Seasoned Citizen NAZ's Avatar
    Join Date
    Feb 2016
    Location
    "The High Country", beautiful Flagstaff, AZ
    Posts
    2,443
    Post Thanks / Like
    After half a century of working on a variety of brake systems I’ve used several methods of bleeding brakes and juice clutches. All work – some are just easier. Since I did this work for a paycheck, I had to be able to quickly bleed brakes by myself.


    I prefer to use the vacuum method as it’s not as cumbersome as pressure bleeding. You still use pressure to force the fluid through the system but it’s atmospheric pressure not compressed air. The vacuum method uses a see-through container between the vacuum source and the caliper. Pull a vacuum on the caliper you want to bleed and control the flow with the bleeder valve then simply watch for air bubbles while keeping the M/C reservoir full. Since you don’t need a cap on the M/C reservoir the process is fast and easy. My first vacuum pump was made from an old Ford mechanical fuel pump but years ago I discovered the MityVac and been using it ever since.

    I also don’t bench bleed the M/C – too much time and work. Bench bleeding seems to have become a mythical “requirement” for some but I’ve never come across a M/C that “required” bench bleeding. The real advantage of bench bleeding a M/C is pushing a bunch of air out of the M/C that would have had to been pushed through the brake system. Let’s take a typical Wilwood 3/4” diameter GS compact remote M/C like FFR may supply in a kit. That M/C displaces .55 cubic inches and the first stroke full of air will fill more than 40” of typical 3/16” brake line with that air. That can make using the old-fashioned pumping the pedal method harder but if you are power bleeding your system (compressed air or vacuum) the most it will do is use a bit more fluid if the brake lines already have fluid in them.


    But like I said, all the popular methods of bleeding brakes work so find one you like and use it.
    Dart Little M 406" SBC 800 HP N/A & 1,100 HP on nitrous, 2-spd Powerglide with trans brake, 6,000 RPM stall converter, narrowed Moser 88 3.90:1 spool with 35-spline gun-drilled axles & Torino bearings, custom parallel four-link, custom tube chassis & roll cage NHRA certified for 8.5-sec (only two FFR Hot Rods have this cert).

    33 Hot Rod Super Pro Drag Racer Build: 33 HR NHRA Cert Roll Cage Build

  11. #11
    Senior Member Avalanche325's Avatar
    Join Date
    Nov 2011
    Location
    Jax Beach, FL
    Posts
    2,103
    Post Thanks / Like
    Quote Originally Posted by chjort View Post
    I might try your method of 1/4 to 1/2 pumps to see if we can get the MC filled before I pull off the output lines to follow Papa's method. Should we have a bleeder valve open during the pumps or have the system totally closed? I'm thinking we would need to have something open to allow for flow into the system
    Bleeders closed, no pressure, actually reservoir caps / diaphragms off. Go nice and easy. I just added a clutch M/C and it worked fine. If not, go to Papas method. Then pressure bleed the whole system.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

Brown County Customs

Visit our community sponsor