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rear tires blocks when breaking
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URUGUAYAN_FASTBACK



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    Post: #1
    rear tires blocks when breaking

    Hi people, i red a post about brakes and i remember my problem...
    When i step foot on the breaks, the rear tires blocks bad... at 5 miles per hour...

    BUT... My car has no proportioning valve... as the matter of fact, i have the valve outside the car and the break lines are connected directly... A mechanical friend of mine told me thar proportioning valves were´t that important but the blocking problem is really anoying, besides, the car doesn´t break properly...

    I also not sure if the booster is original (dont think so) and i dont believe my car was a disc break one either cause there were not 6 cylinder 72 mustangs with disk brakes...

    I just want to break ok for now... what do i have to do first?

    Thanks!
    Offline 01-11-2011 06:02 AM
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    Tnfastbk



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      Post: #2
      RE: rear tires blocks when breaking

      I would check for any fluid leaking first. Then maybe have your drums turned.
      Offline 01-11-2011 06:59 AM
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      URUGUAYAN_FASTBACK



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        Post: #3
        RE: rear tires blocks when breaking

        (01-11-2011 06:59 AM)Tnfastbk Wrote:  I would check for any fluid leaking first. Then maybe have your drums turned.

        Drums are new, i changed them cause the car was sitting for some years... I also checked and tryed to regulate the rear breaks but it keeps blocking, especially one wheel...

        I suppose the luck of the regulator valve maybe important...
        Offline 01-11-2011 07:10 AM
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        OMS



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          Post: #4
          RE: rear tires blocks when breaking

          The proportioning valve is very important.
          I'm not sure of the exact numbers but on disc brake cars, I think it is around 65 % front 35% rear. Might be higher as the front discs do most of the work.
          I would say it is a major safety issue. If you have to stop fast and the rear brakes lock up, the back end is coming around.

          Since you think the disc brakes may have been added.
          First step is to be sure there is no problem with the rear drums, wheel cylinders and hardware. If it is all correct.
          The most economical fix would be an adjustable aftermarket valve installed in the rear line. Then you can adjust the flow to the rear drums to stop them from locking up and force more pressure to the front discs.
          Offline 01-11-2011 07:55 AM
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          URUGUAYAN_FASTBACK



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            Post: #5
            RE: rear tires blocks when breaking

            I have the proportioning valve original from the car but i dont know if it works or not and as its a really simple object, nobody here fixes it... i´d asked...
            Besides, maybe is a drum drum proportioning valve and is not correct with this configuration... I may recheck the rear hardware breaks cause maybe it is an easy solution issue and i dont wanna invent too much on this car, again trying to keep its originality...
            Thank OMS! (i wrote on the vin issue post asking about your sourse for numerical engine codes cause i cant find a "3" on 1972)
            Offline 01-11-2011 08:05 AM
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            Tnfastbk



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              Post: #6
              RE: rear tires blocks when breaking

              Then you might try to re adjust them. I have attached a link its a litle long but might help you do it.

              http://www.onlymustangfords.com/mustang-...lding.html
              Offline 01-11-2011 09:38 AM
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              c9zx


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                Post: #7
                RE: rear tires blocks when breaking

                I agree with Don. You must have the proportioning valve. If I understand correctly the car now has disc brakes in the front and drum brakes in the rear. It also has a brake booster installed. If I'm wrong please correct my assumptions. For the brake system to function properly all the components must be properly matched. The master cylinder must be for power assisted disc brakes and matched to the calipers and wheel cylinders, the the brake rod must be adjusted to the proper length. Do you know why the proportioning valve was removed? Can you send pictures of the front calipers, master cylinder and booster as well as what was installed to replace the proportioning valve? The pictures may enable us to be more helpful to you. Does the parking brake completely release the rear brakes? Do you see any sign of a leaking rear wheel cylinder?

                Chuck
                Offline 01-11-2011 10:15 AM
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                URUGUAYAN_FASTBACK



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                  Post: #8
                  RE: rear tires blocks when breaking

                  Hi chuck! well, pictures can be helpful as you say so i´m gonna try toi take usefull ones...
                  The valve was removed because the break fluid level sensor broke so there was a lick there.. thats what the other owner told me... i didnt know those valves were fragil so i kinda believe him...
                  the front brakes, discs and so looks original so i think the previous owner, when the car was stolen and the front suspension was gone, he took advantage of the situation and upgraded the brakes with NOS parts that he told me he import along with the seats and other parts he recover for the car...
                  Rear brakes looks original too and booster looks good to.. fits perfectly and the pedal and regulators wasnt modified at all...
                  The obvious answer is that if the proportioning valve is missing in the system, rear brakes brake more and front breaks brake less and that the blocking issue...
                  I´ll check the hole system (im not a great mechanic also Tongue) and maybe, if i cant regulate rear breaks, i´ll try to install the proportioning valve and see what happens.. what do you think?
                  Offline 01-11-2011 10:44 AM
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                  c9zx


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                    Post: #9
                    RE: rear tires blocks when breaking

                    (01-11-2011 10:44 AM)URUGUAYAN_FASTBACK Wrote:  Hi chuck! well, pictures can be helpful as you say so i´m gonna try toi take usefull ones...
                    The valve was removed because the break fluid level sensor broke so there was a lick there.. thats what the other owner told me... i didnt know those valves were fragil so i kinda believe him...
                    the front brakes, discs and so looks original so i think the previous owner, when the car was stolen and the front suspension was gone, he took advantage of the situation and upgraded the brakes with NOS parts that he told me he import along with the seats and other parts he recover for the car...
                    Rear brakes looks original too and booster looks good to.. fits perfectly and the pedal and regulators wasnt modified at all...
                    The obvious answer is that if the proportioning valve is missing in the system, rear brakes brake more and front breaks brake less and that the blocking issue...
                    I´ll check the hole system (im not a great mechanic also Tongue) and maybe, if i cant regulate rear breaks, i´ll try to install the proportioning valve and see what happens.. what do you think?
                    I think the brake fluid sensor you refer to is actually a pressure differential switch that turns on the brake warning lamp if air gets into the brake system. While I do not know of a source for new switches, Don at Ohio Mustang Supply may have a good used one he could sell you. While the body of the switch is plastic/nylon they rarely go bad. I suggest you find a switch, reinstall the distribution block/proportioning valve, and thoroughly bleed the brake system to remove any trapped air. Do all the wheels turn freely when they are off the ground?Chuck
                    Offline 01-11-2011 12:49 PM
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                    david020278



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                      Post: #10
                      RE: rear tires blocks when breaking

                      (This post was last modified: 01-11-2011 04:58 PM by david020278.)
                      Offline 01-11-2011 04:55 PM
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