Uneven brakepower left&right

Discussion in 'The whoa and the sway.' started by PatricksBuick, Nov 30, 2019.

  1. PatricksBuick

    PatricksBuick PatrickBuick

    dear V8buick community,

    1967 Buick Special

    I have a new M/C cylinder installed (old one leaked) and also upgraded from the original distribution only valve to an inlinetube distribution/proportioning/Holdof combo valve. That hadn‘t been installed when converted to disc/drum yrs ago.

    Now I have the issue that on the left front side the brake pressure does not go away when I get off the pedal.

    Any ideas?
    How would you go about analyzing what‘s wrong?


  2. pbr400

    pbr400 68GS400

    Brake hose. (Especially if it releases after a while). If so, jack up that side, spin the wheel (to verify it’s free), mash the pedal to lock it. Crack the bleeder and see if it releases.
  3. PatricksBuick

    PatricksBuick PatrickBuick

    Brakes hoses appeared fine.

    I am suspecting the proportioning valve.

    Do these valve require any adjustment after installation?
    If so what exactly needs to be adjusted and how?
    At the front of the valve the is a rubber grommet and a screw underneath it.

  4. Electra man

    Electra man Older and Slower

    The valve will affect the circuits front or rear overall but not individual locations side to side, at least it's not supposed to. You may have some other issue like debris in the line to that location working as a one way valve, the caliper itself or the hose. Break the hose off the caliper and let it drain and flush then assemble rebleed and try again. If the problem is still there disassemble the caliper and clean it out completely. If the problem isn't gone by then replace the hose.
  5. buick64203

    buick64203 Just plum crazy Staff Member

    Just because they appear fine, doesnt mean they are. Theres a quick and dirty method to diagnose this. Like Patrick said, mash the brake pedal and get the wheel to stick. Crack the bleeder. If the wheel frees up, its the hose. If you want further confirmation, mash the pedal again and this time crack the steel line going into the rubber brake hose. If the wheel is still stuck, its definitely the hose
    My3Buicks likes this.
  6. pbr400

    pbr400 68GS400

    I had a hose that appeared fine, too...
  7. woody1640

    woody1640 Well-Known Member

    I've had hoses that looked "brand new" on the outside and collapsed/clogged up on the inside.

  8. Black69Judge

    Black69Judge Well-Known Member

    x3 hose replace both sides
    happened last summer on my motorhome w 33000 original miles
  9. PatricksBuick

    PatricksBuick PatrickBuick

    Alright many people pointing in the same direction. Will do the quick and dirty tetsing and get new hoses first thing next year, just to be safe. Functionality of brakes is crucial.

    However what I did was to open the rubbercap and screw and I heard a pppfffft sound like air under pressure getting released. After that many things improved:
    - cars doesn’t pull to the left anymore when cruising (basically unrivaled)
    - cars stays straight when braking
    - so caliper is now willing to retreat as it should
    Overall driving felt good to normal (haven’t driven the boat in 18 months and boy these cars are veeeery different from my modern Skoda Octavia).

    Any idea what that sound was and how it cured my issues?

    This is the proportioning valve I am talking about


  10. buick64203

    buick64203 Just plum crazy Staff Member

    You released the pressure trapped in the caliper from your clogged rubber brake hose
  11. PatricksBuick

    PatricksBuick PatrickBuick

    So that properly cured the issue?
    Or does it rather confirm there is something dodgy about the hose?
    What is the actual purpose of the screw I opened?

    I drove home for about 20km and couldn‘t feel any troubles...

    Man I hate it when I know there is something wrong and can't get it sorted in the near future....

    Thanks for your help and hope the winter will be short.

    Last edited: Dec 3, 2019
  12. buick64203

    buick64203 Just plum crazy Staff Member

    You opened the bleeder screw at the caliper correct?
  13. PatricksBuick

    PatricksBuick PatrickBuick

    The pppffft sound came when opened the screw under the black rubber. see pic. Ventil.JPG
  14. PatricksBuick

    PatricksBuick PatrickBuick

    We bled the brake system several times before and after the issue which included opening the bleeder screws on the caliper.

    Not sure I answered your question, Jason....
  15. PatricksBuick

    PatricksBuick PatrickBuick

    Attached Files:

    Last edited: Dec 4, 2019 at 9:29 AM
  16. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    No, as long as you have proper pressure on each side of the valve, it centers itself. If you trip the warning light while bleeding the brakes, a simple brake application will re center it and turn the light off. That picture you posted looks like the rubber cap covering the metering pin. The metering portion of the combination valve holds off the disc brakes until a set pressure is attained in the rear brakes. This is because disc brakes are essentially instant acting while drum brakes need to overcome springs and clearance of shoes to drums. The Chassis manual says you should depress the metering pin while you bleed the brakes. Not sure why there is a screw? under the rubber cap?


    The metering valve is separate on the 70 and earlier braking systems. (Next to Master Cylinder). In 1971 and later, it was incorporated into the combination valve.
    Last edited: Dec 5, 2019 at 2:47 PM
  17. PatricksBuick

    PatricksBuick PatrickBuick

    Thanks Larry. Good info, I am getting there... collecting information.
    Wish it was spring and I could actually work on the car.. ;-(

    What are you guys using to measure the pressure (at the end of brake lines)? Is there a specific tool?


Share This Page