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Sarg you can add the brakes and nothing else but it is not advisable. I have a friend in Phoenix with a daily driver 57 pick up that added 4 wheel disc, 2nd gen F body clip in the front, C4 Corvette suspension and rear in the back and he is still using the stock 57 master cylinder. Truck stops really well but it is not the optimum way to do it. The calipers do not know where the pressure is coming from and will still operate, it is more of a safety issue not having the dual master cylinder. A proportioning/combination valve is only needed to balance the front and rear brakes to prevent either from locking up under normal conditions. If the front to rear bias is correct it is not needed either. I have a write up and formulas for determining front/rear bias on a 4 wheel disc system. Involves a little math and measuring all the components in the brake system, including tires.
"WORRYING does not take away tomorrow's TROUBLES;
it takes away today's PEACE."
I really do thank everyone for looking through all their parts for me. I ended getting them from O'rileys.
The plan is. . .my Chevy is my daily driver and my Harley is having starting issues. Seems like when I get one vehicle up and running the other one gets butt-hurt and breaks down to get some attention. I don't want to tear into the brakes until I have a back-up vehicle running.
Also, I know once I get the drums off I'm going to go "Hey, that area could use some cleaning/welding/wiring/whatever" and it'll stay on jacks till the bike breaks down again and I have to put the Chev back together.
What's the easiest way to take a look at this formula?? Thanks!
I copied it from a thread on another web forum. Pasted below, the OP was using and adjustable proportioning valve. The text will illustrate what he was explaining, the formulas are at the end.
I'm not talking about balance between m/c and calipers, but between front and rear calipers. This is way more important. Let's go through the math.
Say you applied 100 lb of force at the pedal. The pedal ratio is about 6:1 (manual brakes) which translates to 600 lb of force at the m/c.
Assuming you have a m/c with a 1-1/8" bore, that gives you 0.994 inČ of piston area (= pi/4*boreČ). So the 600 lb divided by that area gives 603.6 psi of fluid pressure in the brake lines (front & rear).
For the front, the caliper bore is 2-15/16" which gives 6.777 inČ of piston area. Multiplying with the fluid pressure, this gives 4091 lb of force pushing the brake pads. The friction coefficient of brake pads is about 0.4 which, when multiply by the normal force, gives 1636 lb of friction force per pad. Multiply by 2 for both pads, you get 3272 lb of friction force for the caliper. The rotor radius is 5.5" and the friction force is applied at the center of the pads, so about 1" from the outer edge of the disc; or a 4.5" radius. So 3272 lb times 4.5" gives 14 724 lb.in of braking torque. The front tire has a radius of 12.7", so the brake torque divided by that radius gives a braking force at the tire contact patch of 1159 lb. That is for one wheel, so for 2 wheels you get 2318 lb of braking force from the front end.
Repeating for the rear, we get these numbers:
caliper bore: 1-11/16" --> piston area: 2.237 inČ
normal force: 1350 lb
friction force (2 pads): 1080 lb
friction torque: 4860 lb.in
tire force (2 tires): 748 lb (Since there is obviously a mistake in your dimension, I assume the aspect ratio of the rear tire was 45, giving a tire radius of 13")
So, the total braking force from the front and rear ends is 2318 +748 = 3066 lb.
Front bias is 2318 / 3066 = 75.6%
With your prop valve completely close, according to the spec you provided, there would be a 57% pressure reduction on the rear line. So for 603.6 psi, that is a 344 psi reduction (= 603.6 * 0.57) or an available 259.6 psi for the rear calipers. Redoing all the calculations you get a total braking force of 322 lb for the rear (the front stays the same). Total brake force is 2318 + 322 = 2640 lb and front brake bias becomes 2318 / 2640 = 87.8%.
How much bias do you need? The front bias needed is as followed:
Front bias (%) = Front weight ratio + 100 * CG height / wheelbase * deceleration
The front weight ratio for your car must be close to 52%. CG height is about 20" (Usually the height from the ground to where the camshaft is located is a good indication) and the wheelbase is 115". The deceleration is in g's.
So when you initially start the braking process (deceleration is 0 g), The front bias needed is 52% (= 52 + 100 * 20 / 115 * 0). But as the brake force increases, deceleration raises to about 1 g (maximum braking effort). At this point, you need 52 + 100 * 20 / 115 * 1 = 69%. Unless you have an unusually high CG, with a big block (more weight on the front) and really sticky tires (higher deceleration possible), that should be the numbers you are aiming for (say 60-65% with a prop valve and around 65-70% without one).
Because, depending on how much force you put on the pedal, you should need between 52% and 69% front bias (that's what the prop valve adjusts according to the fluid pressure, hence how hard you brake).
But, because your basic system has already more bias from the beginning, you will never be able to achieve that. The results are a system that brakes (almost) only with the front end.
Even with that said, if you know someone who have the EXACT SAME set-up (including CG height, tire compound and size, etc.) and it works, ignore this, there must be an assumption wrong in my calculations.
In fact, if you assume the same friction coefficient for F & R, that value doesn't matter. I did the calculations the long way to make sure everybody was following but to get the same answer you can use this simpler equation:
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