If I have a master cylinder with 50/50 fluid output such as this wilwood
would switching to something like this with a 2:1 fluid output affect brake bias?
My thoughts are, with the 2:1 output, the front should get more fluid with 1 stoke of the pedal. Therefor gain preasure sooner? Im not quite sure im understanding this correctly. So I figured Id refer to all the smart/creative minds here.
Paging Angry Corvair to the white courtesy phone. Angry Corvair, please pick up the white courtesy phone for an important brake related discussion in progress.
So as a little back story to this question. I added 4 piston caliper to the front, which were previously a single piston slider design. But this seemed to result in the rear brakes working more then before.
Car has an adjustable proportioning valve, which worked well with the previous front calipers, now I have it turned almost all the way to cut down the pressure to the rear. Im wondering if its an issue of not moving enough fluid with a MC that has the ratio of 1:1
Sounds like you're on the right track. You should be able to do some rough calcs to figure out what you need.
front piston cross sectional area x number of pistons
Do the same for the rears.
The ratio of front to rear should give you an idea of how much more fluid the fronts need in relation to the rear.
then you can use a proportioning valve to adjust the pressure for fine tuning.
Volume split of MC has nothing to do with when each circuit _starts_ making pressure, and if the MC circuits have the same piston diameters then they will make equal output pressure since they have the same input force.
However, if your new front calipers consume 100% of the volume that circuit of the MC can supply, but the rear circuit still has volume available, then the front pressure will flat-line and the rear pressure will continue to increase (if you continue to increase pedal force). Then you could see the rears doing more work and eventually the car could become rear-skid limited, which can be exciting.
Short answer:
we need to know all piston diameters for all calipers plus the MC so we can accurately compare new vs old
In reply to AngryCorvair (Forum Supporter) :
I expect you also want to know if the pedal was changed.
WillG80 said:Front piston cross sectional area x number of pistons
Do the same for the rears.
Remember that for each 4 piston caliper you only use the area of 2 pistons when making these calculations.
In reply to therieldeal :
More generally, if pistons oppose each other you only use half the piston count.
In reply to AngryCorvair (Forum Supporter) :
rear skid excitement is indeed what im experiencing. FWD nose heavy car im sure isnt helping.
In reply to AngryCorvair (Forum Supporter) :
Front caliper piston dia 40 and 36 mm. (Previous was 54mm)
Rear piston dia 34mm
manual brakes, pedal ratio of 6:1 MC dia 7/8
Front rotar dia 11.025
Rear rotor dia 10.63
Keith Tanner said:In reply to AngryCorvair (Forum Supporter) :
I expect you also want to know if the pedal was changed.
It matters for input force and travel, but not for what the OP is asking.
I've also considered trying a 1" bore. But I wasn't convinced that would fix the issue.
I dont exactly have an issue with trying some math. I'm just not exactly sure where to start with what math would help me figure out a solution to my problem.
In reply to 79rex :
Sorry man, work was really busy after my last post. I'll walk you through the equations tomorrow.
In reply to AngryCorvair (Forum Supporter) :
no worries, any suggestions/help is greatly appreciated.
https://www.tceperformanceproducts.com/bias-calculator/
This calculator works pretty ok. It makes a few assumptions, but most of them won't make a huge difference as far as what you're trying to sort out here. This will give you your brake bias % with no proportioning valve. You're going to need a couple more values beyond what you've provided so far.
My suggestion would be to run the numbers for your stock system as a baseline for that vehicle, then run the numbers for the new/modified system, and compare.
If your bias % works out reasonably close then you've probably got some other issue to chase down.
In reply to therieldeal :
filling that out resulted in new front bias .746. Old bias .704
In reply to AngryCorvair (Forum Supporter) :
While you are here and working on this... (hopefully I am not out of line jumping in).
I have been working through some stuff on my F500, trying to get better braking performance. Basically, right now I am feeling like I have nothing in the rear brakes. I have so far swapped the rear master cylinder from 7/8 to 3/4 trying to get more out of it, but saw no real improvement. I kind of want a sanity check.
Heres what the system currently is.
Willwood bais bar pedal ( I think its this one Pedal ) Pedal 1 Ratio: 6.0 to 1 Pedal 1 Length: 9.60 Mount Length: 10.34
Willwood 3/4 masters running the front and rear circuits. (two 3/4 masters overall linked via bias bar)
Front circuit - One willwood dynalite on a 7.5" solid (non-vented, but slotted and cross drilled) rotor per each front wheel. This Caliper two stainless steel 1-3/4" pistons per caliper.
Rear Circuit - There is only ONE brake rotor and caliper on the solid rear axle (no diff), it is the same caliper as the front, but is on an 8 inch vented and slotted rotor.
Pads - unknown willwood polymatrix, I have a new set going on that are polymatrix "A" slight information on pads
The car builder thinks I may have glazed pads/rotors, so I will be pulling the rotors and cleaning them up and swapping to the new pads while verifying I dont have a stuck rear piston. Basically I should be able to lock the rear with the bias bar set fully rear.
Car is about 65% rear weight and weighs 800-820lbs with driver on an 80" wheelbase. Tires are 8" wide hoosier bias plys on all 4 corners in a 19" overall diameter.
In reply to Apexcarver :
Sounds like if we combine our problems, we'd end up with a well sorted braking system!
79rex said:In reply to AngryCorvair (Forum Supporter) :
Front caliper piston dia 40 and 36 mm. (Previous was 54mm)
Rear piston dia 34mm
manual brakes, pedal ratio of 6:1 MC dia 7/8
Front rotar dia 11.025
Rear rotor dia 10.63
OK, so your old front calipers were single 54mm bore. piston area = pi * (r squared) = 3.14 * 54 * 54 = 9156 mm^2
Your new front calipers are 4-piston opposed with bores of 40 and 36 mm, so total piston area = area 1 + area 2
area 1 = 3.14 * 40 * 40 = 5024 mm^2; and area 2 = 3.14 * 36 * 36 = 4069 mm^2, total = 5024 + 4069 = 9093 mm^2
So, your new front calipers have about 0.5% *less* piston area, which is really within the realm of "round-off error". for the sake of this discussion, lets say new and old calipers have equal piston areas.
now, here's where we make an educated assumption: if we assume that the outer edge of the largest piston is perfectly aligned with the OD of the rotor, then we can calculate the "effective radius" from the center of the rotor to the center of that piston. it is this effective radius that takes the friction force of clamping the pads against the rotor and converts it into brake torque.
Front Rotor OD = 11.025 in * 25.4 mm per in = 280 mm;
Old Caliper Piston OD = 54 mm; then old effective radius = (280-54)/2 = 113 mm
New Caliper Piston OD = 40 mm; then new effective radius = (280-40)/2 = 120 mm
So, your new calipers have the same piston area as your old calipers, ie they make the same amount of clamp force as the old calipers for the same line pressure. but they squeeze farther out on the rotor by about 6%. so in theory (and here's the big disclaimer) with all else being equal (hint, all else is never equal LOL), your new front brakes should be producing 6% more brake force at the contact patch.
now, let me ask you two questions:
you say "FWD nose-heavy car". was that car originally plumbed with a diagonal-split system? I'm guessing yes.
and have you re-plumbed it to be a front-rear split? because you mentioned an adjustable prop to the rear, i'm guessing yes.
In reply to AngryCorvair (Forum Supporter) :
Originally it was 2 lines out of the master into a primitive mid 90s ABS block (neon). In which the ABS unit started leaking. So I got rid of it. So that was eliminated, which was replaced with a wilwood adjustable PV. It uses one in/one out for the rear. Then 1 in/2 out for the front. The original MC isnt being used anymore either.
Essentially what I did was go for the same concept that honed developments used with what they offer to use 986 calipers on the front of civics. The math that they came up up with is here. https://honeddevelopments.com/honed-porsche-caliper-kit-design-and-install/.
They also end up pairing it with a manual pedal 6:1 ratio, and a 7/8 dia MC
I suppose I can add, front pads are Gloc R12, rears are hawk HP+
got a PN for that prop valve you're using?
In reply to AngryCorvair (Forum Supporter) :
260-11179
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