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Thread: Front brakes won't release after disc brake conversion

Discuss the Austin Healey Sprite and the MG Midget. Two different but similar cars sometimes referred to collectively as the Spridget.

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    Senior Member Ohiobugeye's Avatar
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    Front brakes won't release after disc brake conversion

    Hello All, It's been a while since I have used B.C.F. Being I have little knowledge to pass on I'm mainly a member asking questions. I have a 1959 Bugeye with 1275, rib case, elect ignition and a webber carb. I recently converted the front brakes over to disc. My problem is that the front brakes won't fully release. I have been able to drive the car short distances but the brakes are dragging enough that the car will only go about 40 mph with the pedal to the floor. Again just after a short distance the brakes a really hot. I bought a complete disc system off of a 1972 Midget from ebay and replaced the Calipers, rotors and pads, and a new 3/4 " master cylinder along with new rubber brake lines with new parts from Vic. Brit. I was to locally to replace the rubber lines with stainless steel braided lines because the rubber lines were probably collapsing from the pressure increase.The rear brakes are fine but the new front disc brakes still won't release. The entire hydraulic system has been bled many times. If the car sets overnight the car will roll by hand but once the brakes are applied they are locked up again. Any and all suggestions will be appreciated. Thanks< Don Davidson aka the ohiobugeye.
    One Step Forward, Two Steps Backward, but Keep on Pluging Away!!!

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    Yoda dklawson's Avatar
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    Re: Front brakes won't release after disc brake conversion

    Quote Originally Posted by Ohiobugeye View Post
    I was to locally to replace the rubber lines with stainless steel braided lines because the rubber lines were probably collapsing from the pressure increase.
    I don't understand the quoted sentence. What were you trying to say?

    Old rubber lines may collapse on the inside from years of fluid exposure and internal swelling. Such hoses have been known to act like check valves where fluid makes it to the wheel cylinder/caliper but cannot get back to the brake reservoir. However... you said you replaced the lines. Increased brake fluid pressure will not make new lines collapse, it will make them "balloon".

    If the front brakes are locking/dragging after a short drive, try cracking the bleed nipple for one of the front wheels immediately after you get home. Note if fluid jets out of the bleed nipple or not.

    You say you transplanted a complete system from a '72. Are you confident that the MC pushrod is fully retracted when you release the pedal?
    Doug L.
    '64 Morris Mini Cooper-S 1275
    '67 Triumph GT6 Mk1

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    Jedi Hopeful histerical's Avatar
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    Re: Front brakes won't release after disc brake conversion

    ditto. make sure the piston is fully retracting in the master. there should be 'some' free-play there or the piston will not travel in far enough to uncover the return port and the line will remain pressurized. driving around with a dragging brake can over-heat the bearings or warp the rotor.

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    Jedi Warrior Rhodyspit75's Avatar
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    Re: Front brakes won't release after disc brake conversion

    Sounds like you are using the wrong pushrod. Read this article it may help. http://gerardsgarage.com/Garage/Tech/DbrakeUg.htm
    &quot;Age considers; youth ventures.&quot; Rabindranth Tagore
    1975 Spitfire

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    Jedi Trainee Joe Schlosser's Avatar
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    Re: Front brakes won't release after disc brake conversion

    Agree with others, 3/4 inch pushrods are different length (shorter) than the 7/8 inch. If you are using the 7/8 pushrod then the MC will not return fully. good pics on Gerards site.
    Joe Schlosser
    SCCA National License, Retired
    60 Bugeye, since 1966
    SCCA FP, sold but not forgotten

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    Jedi Warrior
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    Re: Front brakes won't release after disc brake conversion

    On another track, I had some issues with one side on my disc brake conversion where the bearings were not fully seating on the spindle due to the taper on the bearing and taper on the shaft. The disc's would barely spin and the disc was not centered between the pads. Just something to check.

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    Senior Member Ohiobugeye's Avatar
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    Re: Front brakes won't release after disc brake conversion

    Thanks for the quick reply's To answer dkdawsons question on the clarity of the above mentioned sentence it should have read "I was told locally to replace the rubber lines". A local mechanic suggested that I replace the rubber lines.
    Great info on the push rods , I'll check it out. The article from Gerardsgarage.com Thanks to all, Don
    One Step Forward, Two Steps Backward, but Keep on Pluging Away!!!

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    Yoda dklawson's Avatar
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    Re: Front brakes won't release after disc brake conversion

    Thanks for the clarification.

    To restate what I mentioned earlier.... OLD rubber hoses may swell inward turning the brake hoses into check valves. NEW rubber hoses won't do that. The stainless overbraid hoses won't do that... ever. However, if you installed new rubber lines already there is NO reason to replace them. They won't close off internally due to "higher pressure" as you were told.
    Doug L.
    '64 Morris Mini Cooper-S 1275
    '67 Triumph GT6 Mk1

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    Senior Member Ohiobugeye's Avatar
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    Re: Front brakes won't release after disc brake conversion

    Problem Solved ! You guys were right on the money.I readjusted the nut on the control rod to shorten the length by about 7/16" and the pads were able to retract. I drove around the neighborhood testing the brakes and after a few minor adjustments the brakes are working fine. The clutch has the same 7/8" control rod but it seem to be working fine. As always , the advice from the Forum solved my problem. I was able to buy a 3/4" control rod from a 65 Midget and I will install it when it arrives this weekend. Thank You, One and all. Don Davidson
    One Step Forward, Two Steps Backward, but Keep on Pluging Away!!!

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    Yoda dklawson's Avatar
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    Re: Front brakes won't release after disc brake conversion

    Great news ! Thanks for posting what you found.
    Doug L.
    '64 Morris Mini Cooper-S 1275
    '67 Triumph GT6 Mk1

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    Luke Skywalker Gerard's Avatar
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    Re: Front brakes won't release after disc brake conversion

    For those who may be unaware, along with supplying the best 3/4" master cylinder conversion available anywhere, I also have new manufactured correct length cad plated pushrods.
    Gerard
    http://gerardsgarage.com/
    1960 Bugeye Vintage Racer #50
    1960 Bugeye (partially restored)
    1960 Morris Minor Pickup
    1964 Morris Minor 4 dr Saloon
    1970 Austin Mini (for sale)
    1946 Austin 10


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