Results 1 to 7 of 7

Thread: Front brakes won't release

Discussions of Triumph motor cars

  1. #1
    Jedi Knight John_Mc's Avatar
    Join Date
    Apr 2005
    Location
    South San Jose, CA
    Posts
    976
    Thanks Thanks Given 
    0
    Thanks Thanks Received 
    0
    Thanked in
    0 Posts

    Front brakes won't release

    Hi all. I haven't been on here in a while so I apologize if this has been recently discussed. My front brakes won't release on my '71 TR6. I have recently replaced the master cylinder and resealed the pressure differential valve, but still when I drive, the situation gets progressively worse until I can't budge. It may be that I need to bleed the lines more thoroughly, but I think there's more to it. Anybody have this same experience and know the most likely culprit and the most predictable solution? Thanks in advance.
    Last edited by John_Mc; 04-26-2019 at 01:24 AM.
    '71 TR6 (CC53680L)
    '91 VW Vanagon Westfalia
    Triumph Motor Company-Zero factory emissions since 1981!

  2. #2
    Great Pumpkin TR3driver's Avatar
    Join Date
    Aug 2003
    Location
    Sunny So California
    Posts
    18,989
    Thanks Thanks Given 
    4
    Thanks Thanks Received 
    73
    Thanked in
    70 Posts

    Re: Front brakes won't release

    Try this simple test: when the problem happens (brakes just dragging, you don't need to wait until it won't move), loosen the fittings on the brake MC briefly and let a few drops of fluid out. Best to hold a rag underneath so the fluid doesn't get on your paint. Tighten the fittings back up, and see if the car will roll freely now.

    If that releases the brakes, then the most likely culprit is the pushrod between the servo and the MC. There is some variation from MC to MC, and the pushrod should be adjusted when either one is replaced; so it doesn't hold the MC piston partially depressed (nor have a gap). This operation is unfortunately not covered in the workshop manual, AFAIK.

    Best solution is to take it apart, make some careful measurements and adjust the pushrod. But as a short term workaround/proof of concept, you can put flat washers in the joint between the MC and servo.

    There is a very little bit more about this in the Buckeye article at https://www.buckeyetriumphs.org/s/Ov...rake-Servo.pdf
    (near the bottom of page 8)
    Randall
    56 TR3 TS13571L once and future daily driver
    71 Stag LE1473L waiting engine rebuild
    71-72-73 Stag LE2013LBW waiting OD gearbox rebuild

  3. #3
    Jedi Hopeful
    Join Date
    Nov 2007
    Location
    VT
    Posts
    126
    Thanks Thanks Given 
    0
    Thanks Thanks Received 
    0
    Thanked in
    0 Posts

    Re: Front brakes won't release

    Also a good possibility that if you still have the rubber brake lines they are starting to collapse internally. They will allow fluid through to pressurize the calipers but not allow it back to release them.
    if the above test doesn’t fail, then consider replacing the rubber hoses.

  4. #4
    Yoda dklawson's Avatar
    Join Date
    Mar 2005
    Location
    Durham, North Carolina, USA
    Posts
    6,036
    Thanks Thanks Given 
    0
    Thanks Thanks Received 
    36
    Thanked in
    33 Posts

    Re: Front brakes won't release

    +1 to both posts above. In particular to Charlie's.

    The flex lines can look to be in perfect condition on the outside... and be collapsed on the inside. The internal collapse turns the flex lines into check valves that allow high pressure brake fluid to reach the wheels... but not release.

    I have experienced this on a few old cars including a '69 TR6 earlier this month.
    Doug L.
    '64 Morris Mini Cooper-S 1275
    '67 Triumph GT6 Mk1

  5. #5
    Yoda Marvin Gruber's Avatar
    Join Date
    Jan 2003
    Location
    Florence, Al
    Posts
    3,083
    Thanks Thanks Given 
    1
    Thanks Thanks Received 
    2
    Thanked in
    2 Posts

    Re: Front brakes won't release

    My bet is the rubber lines. I have replaced a bunch of them.
    Marv

  6. #6
    Jedi Warrior
    Join Date
    Feb 2010
    Location
    Beulah, MI
    Posts
    459
    Thanks Thanks Given 
    0
    Thanks Thanks Received 
    0
    Thanked in
    0 Posts

    Re: Front brakes won't release

    If there's pressure at the caliper bleeders when you're brakes are dragging, it's the flex hoses.

  7. #7
    Jedi Knight John_Mc's Avatar
    Join Date
    Apr 2005
    Location
    South San Jose, CA
    Posts
    976
    Thanks Thanks Given 
    0
    Thanks Thanks Received 
    0
    Thanked in
    0 Posts

    Re: Front brakes won't release

    I replaced the old rubber flex hoses with stainless steel braided hoses (Cobalt brand from Moss) and so far that seems to have resolved the issue. Thanks for all your help.
    '71 TR6 (CC53680L)
    '91 VW Vanagon Westfalia
    Triumph Motor Company-Zero factory emissions since 1981!

Tags for this Thread

Bookmarks

Posting Permissions

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