Kelsey Hayes Disc Brake Upgrade Question

Brakes for your Classic Mopar

  1. John Martin

    John Martin Well-Known Member

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    I am upgrading the brakes on my 1970 Dart that came with 9” manual drums. I have acquired and restored a set of original K-H brakes from a 1969 Swinger 340. I am about to button everything up but I have been reading about brake proportioning.

    An aside: My neighbor’s father-in-law had a Duster with a power K-H system. That car was a 318. He says that you breathed on the brakes and it would try to launch you through the windshield.

    I just want to make sure that the 9” rear drums are appropriate. I have not heard of 10” drums for a 7 1/4” axle. I just don’t want the rear end to swing out in a panic stop.

    Thanks.
     
  2. J Glenn

    J Glenn FABO Gold Member FABO Gold Member

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    A 9" drum should work fine... I think. Just not as fine as a bigger drum;-). I bet you'll be happy, but you will not get launched through the windshield with K&H. You should also be able to aquire the correct MC for that set up. These are manual or power?
     
  3. John Martin

    John Martin Well-Known Member

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    It’s my understanding that the stock 10” rear drums should at the very least have the smaller 9” drum wheel cylinders installed to reduce the sensitivity.

    It will be a manual system, I have the correct master cylinder for it. I am waiting on a few more parts to finish everything up.
     
  4. flingdingo

    flingdingo Well-Known Member

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    I used the prop valve from my '73 Scamp in my wagon when I did the KH swap. The wagon has the stock 9" rear brakes. I've never had an issue with the rear locking up before the front. It stops straight and true every time. Even in a couple of panic situations where I was REALLY glad I put the discs on.
     
  5. halfafish

    halfafish Damn those rabbits, and their holes! FABO Gold Member

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    There are 10" 7.25 rear brakes, I parted out a Volare that had them. They were also on my 69 Dart. Adding a prop valve will solve the problem if the rears are too much for the fronts.
     
  6. John Martin

    John Martin Well-Known Member

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    It is my understanding that all disc brake cars built December 31, 1969 and before use the two piece valve system.

    1st and 2nd pics

    All disc brake cars built January 1, 1970 or later use a one piece valve system where both parts of the old system are basically Siamesed into a larger part.

    3rd pic

    30143FC4-AA5E-4A46-A410-2D25E7D4985F.jpeg

    0DB69657-D0D1-4A9F-8A30-7857FDD17BE9.jpeg

    411BE7D6-AE99-4BC7-B29E-709D02077075.jpeg
     
  7. Dana67Dart

    Dana67Dart Like a fine wine, only getting better with age! FABO Gold Member

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    can't vouch for the change over date but the earlier years did have the 2 separate parts.

    stock in 67 on front disc cars is 10x1.75 rear drum. 9" rear drum just won't have the rear stopping power of the 10", but my guess is you will not notice it.

    with manual brakes you will never launch yourself through the windshield. You might brake the front seat back off but that's about it!

    As long as you use all the correct parts for the same year (with regard to the 1 or 2 piece distribution valve and proportioning valve) you will have a bolt on. Since you have a 70 I would use those parts as it would be the most bolt on AND future parts purchases will be easier. The calipers are the same for the KH years so it matters not that they came from a 69
     
  8. John Martin

    John Martin Well-Known Member

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    Chrysler TSB dated 4-15-1970

    9F025951-4050-4C78-9332-DDFB58FBE5A8.jpeg

    AF3F9E68-6521-4EFD-BF43-2AF159AF2674.jpeg
     
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    • pishta

      pishta I know I'm right....

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      Mr. Kline, "componded" is not a word......:lol:
       
    • Dana67Dart

      Dana67Dart Like a fine wine, only getting better with age! FABO Gold Member

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      There you have it from the chryslers mouth.
       
    • str12-340

      str12-340 FABO Gold Member FABO Gold Member

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      you could always install an adjustable proportioning valve - they are available as a stand alone unit to go in the rear brake line or they make one piece proportioning valves with the adjustment knob built in.
       
    • John Martin

      John Martin Well-Known Member

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      Ok. That’s not what I was asking... I have a factory part to do the job.
       
    • str12-340

      str12-340 FABO Gold Member FABO Gold Member

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      I believe that the combination that you are using is not a combination that Chrysler ever produced. Therefore I presume that there is no "factory part" to correctly proportion between K-h discs and 9" drums. If you have problems at initial testing that shows that the factory parts don't do the job, this is a way to adjust the rear brake pressure so that the phenomenon that you fear will not happen in an emergency.

      As stated in post #5 there were lots of cars with 7 1/4 rears with 10 inch brakes - almost all the 68-71 cars with 318 2bbl and an automatic. I believe all the V-8 cars had 10 inch rear drums regardless of rear axle. Since a lot of 7 1/4 cars with V-8s get switched to 8 3/4 or 8 1/4 and the rear brake don't swap (different bolt pattern for backing plate), I would bet a want ad would get you a bunch of offers for 7 1/4 10 inch rear brakes at low prices. Then it would be a factory available combination and you would probably have no issues with the stock proportioning valve(s).
       
    • John Martin

      John Martin Well-Known Member

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      So the valve clearly silhouetted in a Chrysler TSB is not a factory part?

      I got stood up by some guy in Rockford, IL who claimed to have just what I need. He told me his 69 Barracuda he was parting out had the parts. It’s not for lack of trying, I will see what the car does once I get the rest of the parts in.
       
    • str12-340

      str12-340 FABO Gold Member FABO Gold Member

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      I'll try once more, then drop it. The proportioning valve sends different line pressures to the front and rear brakes. They are made differently for different combinations of front and rear brakes based on type (disc vs. drums) and the size and details of those brakes (eg.1 pot vs. 4 pot calipers & 9, 10, 11 inch drums.) Since, I don't believe that chrysler ever made a car with 9 inch drums in back and KH discs in front there is no actual valve made for what you are doing. Yes the part is a factory part FOR A CAR WITH KH DISCS AND 10 INCH REAR DRUMS, which I don't think is what you are telling us you have.

      I'm just suggesting that with an adjustable valve in place, you could adjust the pressure to the rear brakes and make it work correctly if it doesn't.
       
      Last edited: Oct 19, 2020
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      • 65 Cuda 340

        65 Cuda 340 FABO Gold Member FABO Gold Member

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        For whatever it's worth, my 63 Valiant slant six has KH front discs and the original 7.25 rear with 9 inch brakes. Brakes work great. My 67 360 Barracuda, on the other hand, has the same front brakes and an 8.75 rear with ten inch brakes. It used to prematurely lock the rear brakes on a hard stop until I replaced the rear wheel cylinders with this set I got from Ehrenberg: for MOPAR Disc/ Drum Brakes Lockup Proportioning Fix Plymouth Dodge A, B, E-Body | eBay. (I'm thinking these might just be the standard nine-inch brake wheel cylinders, but I don't know that.) Both cars have disc brake dual master cylinders and the later style OEM combination valve (post 8, above).
         
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        • Dana67Dart

          Dana67Dart Like a fine wine, only getting better with age! FABO Gold Member

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          Their ad says they reduced the id by 13%

          9 inch has of 0.594 (per RA)
          10 inch has 0.906 (per RA)

          13% of 0.906 is a little over 3/4" so bigger than 9" and smaller than 10 inch
           
          Last edited: Oct 21, 2020
        • V8 Sam

          V8 Sam Well-Known Member

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          Stock kH 4 pots up front on my dart

          10inch on 71/4 on the rear too

          Well for now untill the axel is swapped.
           
        • John Martin

          John Martin Well-Known Member

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          I may just take that old axle off your hands then.
           
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          • V8 Sam

            V8 Sam Well-Known Member

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            If you wanna come get it from London you're more then welcome buddy
             
            Last edited: Oct 28, 2020
          • John Martin

            John Martin Well-Known Member

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            London England, haha, too bad it wasn’t London Kentucky
             
            Last edited: Oct 28, 2020
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            • BillGrissom

              BillGrissom Well-Known Member

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              You must have a proportioning valve for a disk/drum setup. Best is an adjustable valve since the factory ones are for a specific setup. Even changing tires or wheel sizes could change the ideal ratio, or shifting weight between front and rear (different engine, AC, different seats, ..). The proof is that many pickups and vans came with a level-sensing proportioning valve (arm senses deflection of rear springs). Ideally, you will run skid-test in a wet parking lot and set the proportioning so the fronts skid just before the rears. If the rears lock up first in an emergency, the rear end can swing around. A basic adjustable valve is $30. You can also buy with an imbalance warning switch for ~$70 (also adjustable). Those might also have the front metering valve, as in the factory "combination valve".
               
            • John Martin

              John Martin Well-Known Member

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              I do have one installed. It is a factory unit. I’m not done with working on the car by a long shot.
               
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