93 Ford Brakes

Discussion in '6.9L IH & 7.3L IDI Diesels' started by thunder, Oct 7, 2006.

  1. thunder

    thunder Registered User

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    I have a 1993 Ford F350 with 304,000 miles. The brake pedal was feeling soft so I took it into the local garage. They checked the pad and shoes and said they were fine but that the booster was bad (said if you took the vacuum line off the booster the pedal was firm, but when connected it would go to the floor with constant pressure). Tried 2 different booster still the same problem, then changed out the master cylinder, again no luck. The mechanic has plugged the lines to the front and the system seems fine, but the problem returns when he plugs the lines to the back so he believes that it has to be in the front brakes. No leaks to be found anywhere. I am tired of buying parts that weren't the problem. Any ideas?
     
  2. Compu Doc

    Compu Doc Full Access Member

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  3. thunder

    thunder Registered User

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    Thanks for the info, I will pass it on to the mechanic.
     
  4. Mont91

    Mont91 Full Access Member

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    I just figured something out. You only have a certain amount of time to type a post. Just lost another post I spent a lot of time condensing and thinking about.:mad:
     
  5. Mont91

    Mont91 Full Access Member

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    Short fast post.

    Your mechanic was full of it.

    OF COURSER THE PEDAL GOT HARD WHEN HE PULLED THE VACUM LINE.

    It is a "vacum booster" how is it going to boost your brake pedal pressure with out vacum????????

    Did you replace the master cylinder. sinking pedal with the back half(rear brakes) plugged means the back half is bad. There should be almost no pedal movement with front or rear plugged. If the pedal moves with the back half plugged, that means the back half is leaking down. Bad master cylinder.

    Continued in next post.
     
  6. Mont91

    Mont91 Full Access Member

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    A sinking or fading brake pedal caused by a bad booster or vacum supply is differant than one caused by hydraulic issues.

    Hydraulic fade first.
    The brake pedal travels to its normal stopping point, or further down, then sinks from there.

    Vacum or booster problem.
    The brake pedal is stiff to very hard from the top. It may stop slightly high then sink to its normal spot as boost slowly builds.
    It will also show up as a high hard pedal that does not get better and takes a lot of miscle to stop or pump a couple times then no boost.

    My pickup had both problems. Bad master cylinder and vacum pump. that was not fun.
     
  7. thunder

    thunder Registered User

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    I have had both the vacuum booster and master cylinder replaced. The pedal feels soft and if you hold your foot on the pedal at a stop, it will slowly sink to the floor.
     
  8. Mont91

    Mont91 Full Access Member

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    Check out the "F250 to F450 master cylinder" post
     
  9. Mr_Roboto

    Mr_Roboto Full Access Member

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    Like Mont said, the mechanic is full of it. A booster can boost less when it wears out, but it can't boost "more" i.e. make the pedal go to the floor.

    The only thing that can make a pedal go to the floor is brake fluid going somewhere. Either bypassing or leaking out.
     
  10. thunder

    thunder Registered User

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    Mechanic said he had plugged the rear brakes at the master cylinder and the pedal will still not hold firm. He still thinks that it is the front brakes. Also now the brake lights want to stay on. Have to bump them several times to get them to go off.
     
  11. 94johnh

    94johnh Registered User

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    Do you have RABS in the truck ? I had a bad rabs module down on the drivers
    side frame ;the bleed down valve was shot so soft brakes, got a re-build from Napa . Life is good now


    john
     
  12. Mont91

    Mont91 Full Access Member

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    If the port that supplies the rear brakes is plugged and the brake pedal still sinks, where is the brake fluid going? It is being forced into the other half of the MC, which is possible only until the pressure equalizes, or it is blowing back past the piston seal. Either of these possibilities means the MC is bad.

    If the pedal does not sink when the front brake port is plugged that means that part of the MC is holding pressure or is good.

    Does the pedal go all the way to the floor? Or does it stop before.

    Will the mechanic build a bypass line for the RABS valve to verify it is not the problem. Did he pull the codes for the RABS.
     
  13. Mont91

    Mont91 Full Access Member

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    Longshot, does the mechanic know that on the newer MCs the front line is for the front brakes? Since the sixties up until the late Eighties the front line went to the rear brakes. When they changed to the plastic reservoir they switched the operation of the MC and the front line now feeds the front brakes.


    The reason I directed you to the other post was because of the disscusion on rear brake adjustment. And the RABS unit.

    If the rear brakes are not adjusted properly,and I do mean properly, you will never have good brakes. Several people on this and other boards have spent a lot of time and money only to find that it was rear brake adjustment causing the problem.
     
    Last edited: Oct 9, 2006
  14. oldmisterbill

    oldmisterbill Grumpy Old Man

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    Real good Point- Too often we get ahead of ourselves,and make assumtions.Guess I am guilty of that to.
    Mr Bill
     
  15. datkinsonsr

    datkinsonsr Full Access Member

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    Just redid my rear brakes and wheel cylinders and thought I had them adjusted. Pedal didn't feel right and parking brake went almost to the floor. Re-adjusted the rears and in the process found the right rear brake mounting plate to be floating on the 4 mounting bolts.-cuss (Very Loose). ;Sweet What a difference correct adjustment makes! Very little pedal needed for good stopping!;Sweet
     

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