68 caddy deville convertable BRAKE ISSUES
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  • 2 Post By carnut
  • 2 Post By mgil
The Classic Cadillac Forum Discussion, 68 caddy deville convertable BRAKE ISSUES in Past Cadillac Vehicle Discussion; Hi all, heres my problem, i have a 68 deville vert , someone has installed an air suspension system in ...
  1. #1
    mgil is offline Cadillac Owners Member
    Automobile(s): 1968 cadillac deville convertible
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    68 caddy deville convertable BRAKE ISSUES

    Hi all, heres my problem, i have a 68 deville vert , someone has installed an air suspension system in it on all 4 corners , they also changed out the front drums to disk brakes, the problem i am having is the rear brakes seem to lock up intermittantly after applying them , sometimes they lock up sometimes they dont . i found that the master cylinder wasnt the right one for front disk , so i changed that out, but this problem still persists , does anyone have any idea what the problem could be ? thanks for your help


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  3. #2
    carnut is offline Cadillac Owners Master
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    Re: 68 caddy deville convertable BRAKE ISSUES

    Maybe the proportioning valve below the master cylinder? I presume you've looked at the rear brakes to make sure no wheel cylinder seepage and that the brake shoe hold down hardware is in good shape?

  4. #3
    mgil is offline Cadillac Owners Member
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    Re: 68 caddy deville convertable BRAKE ISSUES

    I dont believe there is a proportioning valve in the system, doesnt that just send more pressure to the rear brakes than the front , is it really necessary? we did check the rears and all looked good

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  6. #4
    carnut is offline Cadillac Owners Master
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    Re: 68 caddy deville convertable BRAKE ISSUES

    Because it was a 4 wheel drum system before it might not have a proportioning valve. Every disc/drum car I've seen has one.
    CADforce69 and CADforce69 like this.

  7. #5
    Thygo is offline Cadillac Owners Member
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    Re: 68 caddy deville convertable BRAKE ISSUES

    You have to have a proportioning valve the original system was designed for drums. There is a different amount of pressure required to insure proper brake function. Add one and you will fix problem.

  8. #6
    mgil is offline Cadillac Owners Member
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    Re: 68 caddy deville convertable BRAKE ISSUES

    Okay, i'll give the proportioning valve a try, but i cant see how that will prevent the rears from locking up . Isnt the function of that valve to send more pressure to the rears than the front ?

  9. #7
    carnut is offline Cadillac Owners Master
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    Re: 68 caddy deville convertable BRAKE ISSUES

    Log onto www.mbmbrakeboosters.com to read their info. on proportioning valves. Or do a google search " what does a brake proportioning valve do" great info. The MBM web site has a video on updating a drum brake car to disc brakes. It shows what a proportioning valve does and how to mount it.

  10. #8
    mgil is offline Cadillac Owners Member
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    Re: 68 caddy deville convertable BRAKE ISSUES

    i just googled it and guess what ? It says it prevents rear wheel lock up !! thanks for the input guys , obviously my mechanic doesnt know as much as he thinks he does !

  11. #9
    mgil is offline Cadillac Owners Member
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    Re: 68 caddy deville convertable BRAKE ISSUES

    well, i had a proportioning valve added and it did indeed solve the problem ! I cant believe the mechanic i used didnt know this , he is a very talented individual that has years of experience . Anyway thanks guys , i kinda knew in the back of my head i needed it but was talked out of it by this guy. Live an learn!
    CADforce69 and CADforce69 like this.

  12. #10
    carnut is offline Cadillac Owners Master
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    Re: 68 caddy deville convertable BRAKE ISSUES

    Thank you for posting the fix!

  13. #11
    mgil is offline Cadillac Owners Member
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    Re: 68 caddy deville convertable BRAKE ISSUES

    thanks for re educating me !

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