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Expert
Posts: 1348
  
Location: Valley Forge, Pa. | I did the front disc & rear drum AAJ conversion years ago with little noticible difference of 4 wheel drums. A while back, someone suggested to add a 10 lb check valve to the rears. This was a major improvement as far as the pedal felt. Before it would go way down. Now it is up and I am feeling it brake emmediately but it still will not lock up and they have never been very solid. This past week, I dropped it off at my friends garage and he installed an adjustable proportioning valve and one of the caliper bleeders broke, so he installed 2 new calipers. With the new pro. valve, it feels the same as far as stopping power but now I have this short play until it hits a more soild feel. I wondering if that is where the adjustable part comes in? Before the pedal had some resistance until it started to brake but with the new pro. valve there now is an inch or so of free play before I feel any resistance.
I'm guessing MOPARs should have as solid a brake as any car of that era? When I did the AAB conversion, I replaced the rear wheel cylinders and the new front calipers but it is still mushy. All the front brake lines. We've bled gallons through it with several different techniques and nothing gives me a solid pedal or even the feeling it would lock up if I had to. I used the calipers that the AAJ kit said to use. I am still running 3/16 brake lines, should they be larger? According to all that I've read, unless i am going to major brakes, there shouldn't be any issues with the smaller lines?
Thanks again for any suggestions,
Karl. |
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Veteran
Posts: 174
Location: Camptown PA | 3/16 inch lines are fine for your setup. Are you running a master cylinder made for disc and drum brakes, and is it plumbed correctly (large reservoir to disc brakes, small to drums)? If you have a master cylinder designed for front disc and rear drums it will have a check valve for the drums built in and your 10 lb check valve is not needed. Finally have you checked your brake pedal free play? When I put the AAJ conversion on my 60 dart I plumbed in a proportioning valve from a 1974 dodge and had some of the same issues you describe. I got an adjustable master cylinder rod, set the brake pedal free play and my problems were solved. Hope this helps. |
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Expert
Posts: 2120
Location: atlanta | Phatton - 2014-08-31 1:27 PM
3/16 inch lines are fine for your setup. Are you running a master cylinder made for disc and drum brakes, and is it plumbed correctly (large reservoir to disc brakes, small to drums)? If you have a master cylinder designed for front disc and rear drums it will have a check valve for the drums built in and your 10 lb check valve is not needed. Finally have you checked your brake pedal free play? When I put the AAJ conversion on my 60 dart I plumbed in a proportioning valve from a 1974 dodge and had some of the same issues you describe. I got an adjustable master cylinder rod, set the brake pedal free play and my problems were solved. Hope this helps.
What is this brake pedal free play and how much is needed ? |
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Expert
Posts: 3400
Location: Chestertown, NY ( near Lake George) | Free play is usually 1/4 in. min. |
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Veteran
Posts: 174
Location: Camptown PA | Brake pedal free play is how far the brake pedal moves before the master cylinder rod starts putting pressure on the brake fluid. No free play and your brake lights stay on all the time. Too much and you run out of pedal (your foot touches the floor and the car is still moving). The service manual calls for brake free play of 1/8 inch, but remember that is for a car with drum brakes. We've changed the system by adding disc brakes to the front. Get an adjustable master cylinder rod. This is a 2 piece unit. One piece has male threads on it like a bolt. The other piece has a tube with female threads in it. Screw the 2 ends together and install the rod between the brake pedal and master cylinder. Lengthen the rod as far as possible. Your brakes lights should now be on. Start shortening the rod until your brake lights go out and stay out (helps to have a helper for this step). Drive the car. If you're running out of pedal, lengthen the rod. If your brake lights come on when you're not stepping on the brake, shorten the rod. Make small adjustment at this point. My 60 dart with the AAJ front disc conversion is very finicky about this setting. There is not much difference between brake lights on all the time and running out of pedal (about 1/4 turn if I remember correctly). Hope this helps. |
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Expert
Posts: 2120
Location: atlanta | Do You use this adjustable rod with the original rod also? it needs the end to bolt to the brake pedal, right? The Proportioning valve I have has a brake light swich in it, the original is still attached under the dash and works off of the pedal movement, I'll wait and see which one works best. Also my disk/drum master cylider has no provision for attaching the end of the red as the original single pot did, I assume the rod will stay postioned in the end of the MC by itself. |
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Veteran
Posts: 174
Location: Camptown PA | The adjustable rod replaces the original rod. You can find adjustable master cylinder rods in some of the forward look cars with the power brake option. The method of adjusting pedal free play I detailed will only work if you are using the pressure style brake light switch. |
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how will adding the pro.valve affect the feel?
