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  1. #1

    Default Lincoln MK VII proportioning valve in a 4WDiscs 68 Mustang

    Hello,

    At the shop we've had this 68 Mustang that the owner wanted to convert the brakes from manual drums all around to power disc brakes at the four corners.
    We bought an SSBC conversion kit (big mistake but now we're stuck with it), installation was allright even if it lacked instructions but problems started when we tried the car.

    It's actually two seperate kits, one for the front and one for the rear. It does have an adjustable proportioning valve.

    After some research, it uses the 68-73 front calipers and what looks exactly like mid 80s Lincoln MK VII rear calipers. So pretty big ones.

    But the master cylinder was only appropriate for the front discs. The braking power was very poor. With brakes only operating at the end of the pedal travel despite flushing the system countless times and making sure the rod is adjusted properly.

    Hoping to solve that, we've bought a Mustang SVO 1"1/8 master cylinder, it's better as you can feel the brakes working right away but you have to press hard to get any kind of real stopping power.

    At the moment, the only thing in the system that hasn't been replaced is the original differential pressure valve (which after inspection is very clean), the brake line that goes to the right front caliper and the front to rear brake line.

    So we're thinking we should get a real Lincoln MKVII proportioning valve to match the rear calipers.

    What do you think ?
    Do you have any suggestion on something we may have forgotten ?

    Thanks !

  2. #2
    FEP Power Member mcb82gt's Avatar
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    Did you gut the original valve? It needs to be gutted, then adjust with your adjusting prop valve.
    Mike

    Now stang-less.

    88 Cougar 5.0

  3. #3

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    There's no proportioning valve, only a differential pressure valve, which does nothing more than check the pressure for the brake light sensor (which is on all the time by the way).

  4. #4

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    Hello, what is the latest on your brake mods? Have you been able to make the car brake safely? I've changed a couple systems completely, it can be cheap advice, but have disastrous consequences. If you change out to disc brakes, you must install a proportioning valve. And no one will tell you to set the brakes evenly in wet pavement. If someone can watch the brakes set evenly in the wet, will they do the same when in a panic stop? You are on your own for legal reasons. Absolutely best wishes!!!

  5. #5
    FEP Senior Member OX1's Avatar
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    Quote Originally Posted by SuperDuty455 View Post
    Hello,

    At the shop we've had this 68 Mustang that the owner wanted to convert the brakes from manual drums all around to power disc brakes at the four corners.
    We bought an SSBC conversion kit (big mistake but now we're stuck with it), installation was allright even if it lacked instructions but problems started when we tried the car.

    It's actually two seperate kits, one for the front and one for the rear. It does have an adjustable proportioning valve.

    After some research, it uses the 68-73 front calipers and what looks exactly like mid 80s Lincoln MK VII rear calipers. So pretty big ones.

    But the master cylinder was only appropriate for the front discs. The braking power was very poor. With brakes only operating at the end of the pedal travel despite flushing the system countless times and making sure the rod is adjusted properly.

    Hoping to solve that, we've bought a Mustang SVO 1"1/8 master cylinder, it's better as you can feel the brakes working right away but you have to press hard to get any kind of real stopping power.At the moment, the only thing in the system that hasn't been replaced is the original differential pressure valve (which after inspection is very clean), the brake line that goes to the right front caliper and the front to rear brake line.

    So we're thinking we should get a real Lincoln MKVII proportioning valve to match the rear calipers.

    What do you think ?
    Do you have any suggestion on something we may have forgotten ?

    Thanks !
    You would think with the mustang SVO calipers being about the same as a MK VII ( I believe they are in piston sizes anyway), it should all work pretty good. But the only way I could get reasonable pedal pressure, was going mustang hydroboost (I also tried that SVO MC first). Ended up using Stang HB and MC that comes with it. Used stock distrib valve and adj rear prop valve (which I think you have already).



    Also added HB specific sag pump (dual return from I think 76ish Lincoln). Can get sag bracket from widlhorses (early bronco supplier) and the rest of the brackets to work with stock EFI AC compressor (if using it) from early throttle body V-8 cars.



    This also fixed the possibility of the whiney Ford pump, which seems to happen often enough, even with a fresh rebuilt.

    In another application (big offroad bronco with large chevy calipers on all 4 corners), I had to put in a monstrous 90's F350 booster to again, not have a rock hard pedal with SVO MC.

    I've always wondered what size booster did the SVO come with and were they known for having heavy pedal feel (comparatively to GT's of the same years).
    86 Capri, 5.0, 5Spd, A9L QH/BE, 47 lb Inj PMAS 3" MAF, Single T44 Turbo, Front Mount IC, TW170,
    Stock Cam, Explr Intake/TB, 1.7 Rockers, CF dual friction clutch, 3" DP, 2.5" full Exh, 3.27, 11.932 @ 115.78
    84 LTD, 331-10:1, TW170/Exprl Intake, 47 lbs inj/80 mm LMAF, Full Duals, Quarterhorse, Vortech 7PSI, Lentech AOD, 5 lug Mk VII brakes/rear, Eibach Sway bars, Cobra HB (dads ride, but I fix it )

  6. #6
    FEP Super Member xctasy's Avatar
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    Dunedin 9011, New Zealand, South Pacific
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    Your combination is mis-matched. The problem is the lever arm and manner in which the big brake booster apportionions front to rear brake bias in a crash stop. The European system designs a brake system ti front lock-up, which gives a solid pedal. The American and Australian system apportions to cause rear lock-up. The brake bias is normally adjustable best by a ĢM Pontiac, Holden or Opel brake proportioning valve.

    Id skype Jack Hidely and ask for one off advice which he will most likeky give for free. The Kelsey Hayes and historic 1973 booster can work fantastic, but an XK based Mustang suspension system causes steering instability and nose dive which then has to be weeded out by reseting the system bias.

    In my 1984 Falcon XE, I had to add 5 degrees caster, nolathane pitman and idler arms, a non residual booster and the higher assist power steering with a later model brake disc system to get a solid pedal and directional stability when braking.

    Even between the 250 in line six and 351, the brake propotioning system was set up differently at yhe factory. When imported to Europe via Ford ASVE, the 5.8 Ford LTD had totally different front to rear proportioning valve settings. Its called an International Lane Change. You drive at 160 km/h and wind on full lock and apply the brakes. The valve is set up so the car inscribes a gracefull arch.

    The booster and pendant ratio and proportioning is controlled by many parts in your brake system. Jack can help easily. I cant...because it gets techno real quick.

  7. #7

  8. #8

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    You need to start by determining what the piston diameter of the front calipers is. If it isn't possible to measure this, you may be able to figure it out from the brake pad part number. In the US there is an organization called FMSI (friction materials standards institute). They publish a book with the shape of the backing plate and friction material, along with some other basic stuff such as overall thickness. They do this for virtually all OEM brake applications. Each pad design is then given an FMSI number. Many, many aftermarket pad retailers take the FMSI number for the pad and add some prefix or suffix to it to generate their part number. So if you have the part number from the pad, you can usually work backwards through an FMSI book to determine the original caliper application.

    It sounds like the rear calipers are the massive 54mm Kelsey Hayes models. These were used on the SVO and other Lincolns along with matching 73mm front calipers and a 1.125" m/c. If your brake pedal is still going a long way to the floor, then you probably have front calipers with pistons larger than this. You will either need a larger m/c, which isn't easy to find, or smaller front calipers.

    No matter what, lots of good photos of the brake parts already installed on the car is going to be the best starting point.

    There is virtually no chance that a proportioning valve has anything to do with the problems that you are describing.

    Edit: If you mean that the car has 1968-73 Mustang front brake calipers on it, these have 2.375" front piston which is only about 60mm and used an 11.3" rotor. Without a proportioning valve and possibly some other changes, this car will be a death trap with this combination. Waaayyyy too much rear brake bias!

    You have got to install larger front calipers or smaller rear calipers on the car. You will never be able to make them work properly, assuming you have the parts listed above. This has got to be fixed before you determine the optimum m/c size.
    Jack Hidley
    Maximum Motorsports Tech Support

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