brake system math

[dyermullet]

I want to put together some good brake system numbers.  Possibly when this is complete can re-post to the knowledge base. 
For now I am just going to focus on the factory GM g-body vacuum brake system.
I have converted my car to the blazer front brakes, and S-10 rear wheel cylinders.  I want to put the numbers together for the OEM setup as a baseline, and then compare to the blazer brake and S-10 wheel cylinders. I didn't notice a pedal feel difference going to s-10 wheel cylinders but after the blazer brakes I now have more pedal effort.  The exercise is to calculate the different in pedal effort and travel before and after, with the moving the system closer to the feel of the original.


Here is the equations I have put together so far.

Line pressure (psi) = Leg Force (LB) X Pedal Ratio / MC Area (in^2)

MC volume displaced (in^3) = MC stoke (in) X MC area (in^2)

Force at Caliper (lb) = line pressure (psi) X caliper piston area (in^2)

MC stroke (in) = caliper stroke (in) * caliper area (in^2) / MC area (in^2)


I am not concerned with the amount of force added by the vacuum booster because it is a constant/unchanged between both system.
Average leg pressure applied to pedal is between 100-150 lb.  I will use 100 in the equations
Pedal ratio is a constant between the systems, but I will enter the actual value.


I searched for over an hour on tb.com and could not find where anyone has posted the pedal ratio of the factory vacuum brake pedal.  Does anyone know if not I will try to measure mine this week.

G-bodyMC bore is 15/16" - Someone please confirm and it is a single bore 15/16" for both halfs or is the MC dual bore?
Stock calipers piston 2 1/2"
Blazer calipers 46mm piston X2
This is only a 4% increase in area so that equals a 4% increase in pressure on the caliper to the pad.

g-body rear wheel cylinder 3/4"
S-10 rear wheel cylinder 7/8"

I will start searching and filling in the values as I find them.

G-body vacuum disk brake system front:
Line pressure (psi) = 100 (LB) X Pedal Ratio / 0.6899 (in^2)

MC volume displaced (in^3) = MC stoke (in) X 0.6899 (in^2)

Force at Caliper (lb) = line pressure (psi) X 4.906 (in^2)

MC stroke (in) = caliper stroke (in) * 9.812 (in^2) / 0.6899 (in^2)

Blazer disk brake conversion front:
Line pressure (psi) = 100 (LB) X Pedal Ratio / MC Area (in^2)

MC volume displaced (in^3) = MC stoke (in) X MC area (in^2)

Force at Caliper (lb) = line pressure (psi) X 5.14 (in^2)

MC stroke (in) = caliper stroke (in) * 10.28 (in^2) / 0.6899 (in^2)

G-body vacuum drum brake system rear:
Line pressure (psi) = 100 (LB) X Pedal Ratio / MC Area (in^2)

MC volume displaced (in^3) = MC stoke (in) X MC area (in^2)

Force at drum (lb) = line pressure (psi) X .8224 (in^2)

MC stroke (in) = caliper stroke (in) * caliper area (in^2) / MC area (in^2)
S-10 wheel cylinder conversion rear:
Line pressure (psi) = 100 (LB) X Pedal Ratio / MC Area (in^2)

MC volume displaced (in^3) = MC stoke (in) X MC area (in^2)

Force at drum (lb) = line pressure (psi) X 1.202 (in^2)

MC stroke (in) = caliper stroke (in) * caliper area (in^2) / MC area (in^2)

[Charlief1]

One of the things you need to figure out is line pressure for the single VS the dual piston calipers. To help with the front brakes working better you might switch to an F body master or a Blazer master of the right year since both were for the bigger front brakes. I think you'd be better off with the first couple of years of the 4th gen F body since it had 11" brakes and drum rears.

[dyermullet]

pressure PSI is generated by the MC and is constant no matter what the calipers are.  The amount of force applied at the caliper is the result of its total piston area.  I want to replicate the pedal force and travel of the OEM g-bod system.  But as a comparison can calculate the blazer system, but it won't be apples to apples since different boosters.

So far if the numbers I have found are correct should be very little effect on the pedal.  Maybe my increase in felt pedal pressure is from swapping to stainless lines from rubber.

I also want to see how the factory system compares to the recommended working pressures of the aftermarket companies.

[dyermullet]

delete please

[dyermullet]

sorry
delete this one also

[Charlief1]

Well yes and no. A disc system requires a different master due to the fact that 4 wheel discs use pressure more than volume and a disc drum set up needs more volume to the rear than pressure. While the overall line pressure may be the same there's a velocity (reaction time) difference for larger calipers.

[GavinHunyady]

and how much more grip do your 275 drag radials make compared to the 215 all seasons that the original bias was designed for?