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soft/low brake pedal

Discussion in 'VR - VS Holden Commodore (1993 - 1997)' started by sxi ss, Sep 2, 2011.

  1. pete30nz

    pete30nz Member

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    Hi Ephect,

    New hoses have been put on about a month ago, new seals in all calipers.
    I'm still waiting to lend a booster and master as a set to fit to my car and see if it cures the problem.

    Pete
     
  2. pete30nz

    pete30nz Member

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    Hi people,

    This is starting to get to me,
    I've now tried a brake booster and master that came as a set out of a car that was driven a couple of weeks ago.
    I fitted the parts an hour ago, and the pedal still goes soft, at times it feels firm with some travel. Most of the time it goes soft and can press it to the floor.

    What is next...

    Pete
     
  3. Brisbarnz

    Brisbarnz Active Member

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    I just did a re read an you mentioned vt master was 15/16. My understanding is vt was 1 1/4. Any chance you can take a pic of booster n master?
     
  4. pete30nz

    pete30nz Member

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    Hi Brisbarnz,

    The one on the right in the pic is the one I've swapped in to the car now. It looks the same as the original one that came out.
    Master: 15/16. Booster: VH512 it's a big bodied case booster. I can get a better photo if need be.

    This is a VR v6
     

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  5. greenacc

    greenacc Searching for the billion

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    did you notice any difference between with the other master and booster on it?

    Long time ago our family had a toyota corona. The brakes slowly became really bad and it would take ages to pull up.
    Eventually my boss had a look and pulled out the fitting that attaches the booster hose to the intake manifold.
    it was near completely blocked with carbon so the booster wasn't getting vacuum. We drilled out the fitting and like magic the brakes were great again.
    The point is you might need to look for the unexpected little details now as it sounds like you've checked all the major items.
     
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  6. Brisbarnz

    Brisbarnz Active Member

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    A vh512 was fitted factory to my vn v8 with a 1" master. My wife's vq v6 has same booster but a 15/16 master. My vh with a Vx brake upgrade is completely different again. Here is some pics. I'm convinced the pic of your booster on the right is just factory v8 item. Vt style booster have a backwards case (metal). Some of my car for eg.
    %5BURL=http://s1280.photobucket.com/user/B...ABE7-44BAA5069AF4_zpspkufe5if.jpg[/IMG][/URL]
    %5BURL=http://s1280.photobucket.com/user/B...8CE5-CEEB4104052C_zpsd6asdxyd.jpg[/IMG][/URL]
    %5BURL=http://s1280.photobucket.com/user/B...B16C-57806EB51DC5_zpsrxykaazu.jpg[/IMG][/URL]

    %5BURL=http://s1280.photobucket.com/user/B...9839-F8F8408C35B3_zpsvjdtgxtl.jpg[/IMG][/URL]
    %5BURL=http://s1280.photobucket.com/user/B...9F5D-BD4674B5F879_zpsyjaij7ga.jpg[/IMG][/URL]
    The pic of the sticker on the booster is the vx.
     
  7. Brisbarnz

    Brisbarnz Active Member

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    Pics didn't work. I'll fix it when I can.
     
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  8. immortality

    immortality No more smoky bacon :( Staff Member

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    Have you looked for leaks?
     
  9. pete30nz

    pete30nz Member

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    Hi Greenacc,

    The only difference I remember is the pedal still having at least 2 inches of travel, but every few presses it felt firm.the next couple of presses it went soft again with the same amount of travel.
     
  10. pete30nz

    pete30nz Member

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    Hi Immortality,
    I have had a quick look while if climbed under to start bleeding, but have not seen any wet stuff around brake calipers. Friday after swapping over booster and master, after pressing pedal I looked around master and saw no wet on lines below the master.
     
  11. immortality

    immortality No more smoky bacon :( Staff Member

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    Well this is just ******* weird :(

    The pedal going to the floor means either air in the system or something is bypassing fluid/failing. Air would give a more spongy feel so this seems less likely so then we are back to either a brake caliper issue of master cylinder issue.

    I assume all this testing is been done with the engine off so the brake booster shouldn't be having any effect on the brake pedal?
     
  12. pete30nz

    pete30nz Member

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    Immorality,
    Another quick break down:

    Front hoses are brand new, rear hoses are standard. Brake master cylinder and booster came off a recently driven car that had a good pedal.
    I clamped front hoses, started engine and pedal was solid. I then unclamped front hoses and clamped rear hoses, started engine and pedal wasn't as firm.
    Brake bleeding has been done with and with out engine running.
    One lot of bleeding was done pressing pedal half way down each press.

    I have not bled system this weekend yet with working booster and master from recently driven car with good brake pedal.

    Pete
     
  13. immortality

    immortality No more smoky bacon :( Staff Member

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    If you have changed any part of the system and removed any lines than the system will need to be re-bled to get out any air that will have gotten into the system.

    You can't compare how the system operates with and without the engine running because of the influence of the brake booster. IF you bleed the system with the engine off and the pedal is nice and firm, then start the engine the pedal will suddenly have a bit of travel because the brake booster is now working. This is normal. What is not normal is the pedal sinking all the way to the floor with little effort. Having said that, if I stand really hard on a brake pedal I can get it almost to the floor but that means applying more force than you ever would driving the car.

    IT will always have a little more travel with the rears clamped then the fronts clamped simply because of the difference in displacement in the system. The rear piston is probably about half of what the twin piston front calipers displace. That's simply hydraulics physics really.
     
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  14. pete30nz

    pete30nz Member

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    I will get round to bleeding the system , I didn't have a mate to press pedal for me, and ran out of day light.
    Also I will try clamping each hose to see if there is another fault, if bleeding with new booster and master doesn't fix it.

    I'm really hoping it does fix it,

    Pete
     
  15. ephect

    ephect Donating Member

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    jump on ebay and grab itself a brake bleed vacuum pump. ~$23 best thing I bought, used it last week to change the fluid in my vs, was a piece of piss to do.

    do u have an abs system? Maybe u have air in the unit?
     
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  16. pete30nz

    pete30nz Member

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    Hi Ephect,
    Yes it has abs, so I'll bleed it, then drive it, lock abs up on grass, come back and bleed it again.
    I'll look into getting a brake bleeding vacume pump.

    Pete
     
  17. pete30nz

    pete30nz Member

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    Hi people, it has been a while, sorry for the delay. I finally now have a brake master and booster, and also another abs pump on my car, that came off a working recently driven car. Bled the brakes up today, and the pedal still has quite a bit of travel, as in 2 and a half inchs, but it is stopping the car with out to much effort. I will try new pads as well some time soon.
    And will take it to a different warrant shop as well.

    Pete
     
  18. VS_Pete

    VS_Pete Donating Member

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    Thanks for letting us know
     
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  19. pete30nz

    pete30nz Member

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    If any one with abs brakes on a VR or VS v6, how far down does your pedal travel, before it starts to brake at all?
    IM still going to get a vacume bleeder and try to better it.

    By the way, my car did get a warrant on it today, im waiting to see what the brake readings were.

    Pete
     
  20. immortality

    immortality No more smoky bacon :( Staff Member

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    Stock VS brakes always had more travel than I liked. Ours was much better with a VT style booster and MC on it. It's been a fair while since I've driven one though so couldn't really tell you how much.
     
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