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How can one find out the m/c bore sizes of various gm vehicles? I have been searching for a few years simply trying to find out the size of the stock m/c on my '99 C5 and this is the first time I have ever seen a size mentioned. Going up to a 1-1/16" or even 1-1/8" would make for a preferable pedal in my case.
Interesting insight to the ABS systems and such. Seems to remain a bit of a black art of sort at figuring it out totally! Typical computer based systems today it seems.
As for finding alternate bores the easiest way to narrow your search I've found is to look over 'big' cars and often those with drum rear brakes. seeing that the drums (wheel cylinders) require greater fluid displacement than discs the build tends to have larger MCs. Same for the big car market; larger two piston calipers (larger pistons) are usually associated with larger masters.
Here's a question for you. I have a 2002 Z06 which is a dedicated race car (NASA ST-2). I run Stoptech ST-60 front and ST-40 rear. I've never been happy with the long pedal from the stock master cylinder after the upgrade so recently I upgraded to a truck master cylinder with a 1 3/8 piston (stock is 1"). As expected the pedal is insanely hard and I'm still trying to decide if I want to keep it or not. I chose this MC because it was the same one used in the DRM unit. The only reason I didn't choose the DRM unit is because the include a proportioning valve under the hood. I intend to plumb a proportioning valve into the cockpit where I feel it's more useful. My question is this: given the fact that the Z06 has proportioning built in through the ABS unit, will the use of a separate proportioning valve BEFORE the ABS unit help pedal feel (softening it up a bit)? Do you even recommend it since there is dynamic proportioning built into the ABS unit?
I run the same calipers that you have except my rears are AP 4 piston. I went from the truck master back to stock master and my pedal is great. Pedal was way too high and difficult to modulate with the truck master. You shouldn't have a long pedal with the stock master so you might have had another problem. A rear prop valve would not help pedal feel and would only be useful if you pulled the abs fuse in adjusting front to rear bias.
It would also do it under trail braking iirc. I quickly changed the rear pads so I'm working off of brain power that is a few years old
I plan on putting in the proportioning valve soon and trying to run the same compound all around (so I can be just like Bill!).
It's a good setup. I would look into the AP prop valve that Joel mentioned. I still run different pads front to rear out of habit. But I agree with Johnny C that pads with less bite and good modulation and high temp consistency would be best. I would like to try PFC-11 pads all around.
Here's a question for you. I have a 2002 Z06 which is a dedicated race car (NASA ST-2). I run Stoptech ST-60 front and ST-40 rear. I've never been happy with the long pedal from the stock master cylinder after the upgrade so recently I upgraded to a truck master cylinder with a 1 3/8 piston (stock is 1"). As expected the pedal is insanely hard and I'm still trying to decide if I want to keep it or not. I chose this MC because it was the same one used in the DRM unit. The only reason I didn't choose the DRM unit is because the include a proportioning valve under the hood. I intend to plumb a proportioning valve into the cockpit where I feel it's more useful. My question is this: given the fact that the Z06 has proportioning built in through the ABS unit, will the use of a separate proportioning valve BEFORE the ABS unit help pedal feel (softening it up a bit)? Do you even recommend it since there is dynamic proportioning built into the ABS unit?
The C5 and C6 all have very small front caliper bores, because of this I would avoid (at all cost) increasing the size of your master cylinder. This will kill the Hydraulic advantage (TQ) with your front brakes. Does your pedal travel distance increase? Meaning that the first few stops the pedal travel would be consider normal, then after repeated braking the pedal distance required to stop increases? that might be your rotor and replacing your MC would be throwing good money after bad.
It could just be the fact that I needed a new stock MC. Now I have to go back and make new lines to replace what I just modified to fit the truck MC. I might just try what Ben is offering. It might be a good compromise.
How much cooling is too much? On a big braking track like Watkins Glen, I was tempted to put some serious fans inline with my duct work. Testing them on the bench, they produced so much volume that I worried about larger temperature deltas and thus increased thermal fatigue.
Also, is it the case that some pads, like PFC01's, get abrasive if the rotor temp is not high enough?
I am running AP 355 J-Hooks up front with block-off (quantum) spindle ducts. The rotors are doing way better than anything I have had to date, but would not mind extending their life further if possible.
If you have cheap pads like carbos or hawks then you want to keep your pads above 200*. Anything under that they will clean off your their transfer layer. if your running pro level pads like PFC or Padgid cool them off as much as you can. They don't have transfer layer issues and should be cooled as much as you can.
No the pfc's wont chew up a rotor is they aren't hot. the working tep range of the pfc 01 is 100*-1600*. keep it in that range and your rotors will be fine. FYI you'll hit 100* rotor temp driving around the pits on a 70* day.
It could just be the fact that I needed a new stock MC. Now I have to go back and make new lines to replace what I just modified to fit the truck MC. I might just try what Ben is offering. It might be a good compromise.
OK it’s time for this. I THINK THIS FORUM IS READY FOR THIS INFORMATION. IMO Rotors are the single most important aspect of a braking system. They are the most dynamic (they move) component, and are the leading cause for problems. Rotors are a wear item, because of this people go out and buy the cheapest rotor they can, and here is why it’s a big mistake. Rotors grow, it’s important to know how to reduce the growth, and what to look for in a rotor.
Rotors move it’s called thermal expansion. In extreme examples a rotor cam move 2-3mm (.07”-.11”). for a reference of how bad that is wildwood sends .013” shims to shim a caliper. When a rotor does grow it will want to expand radially (Outwards), when the rotor cannot grow outwards anymore it will bend over. This bending has a few names I (and engineers) call it 1st form of deformation, most brake guys call it “coning”. It’s called coning because it start to take a cone shape and bed to the hottest side. As a rotor gets hotter it will enter 2nd form of deformation. The 2nd form the rotor will start to look like the edge of a cowboy hat. (picture A below), the stages of deformation continue past 15th form, anything past 2nd form of deformation the rotor will have a wave look to it (picture b). for reference on temperature and how hot a rotor needs to be to deform. the picture b is from an autocross, max temperature of 600*. The starting temperature of deformation is 100% built on the engineering of the rotor. SO what, why should I care? When a rotor deforms it causes drag, this drag kill the life of pads & rotors, drag will kill hubs, and drag will also not allow the car to accelerate after turns. The deformation can also cause pad “knock back” or “long pedal”. This is when the rotor starts to kick the pads back into the bores of the caliper. This knock back will make your pedal travel further. Sometimes I hear drivers say “ I need to hit the brakes before the braking zones to give me a better pedal". I hate this kind of thinking, that driver isn't Ernestine, he didn’t discover gold, and his rotors are garbage.
picture A of 2nd form of deformation.
Picture B, this was sent to me from a customer that used his car for street survival school.
How to control coning,
How a rotor will deform is built into the rotor when you buy it. So be on the lookout for a good quality rotor. This is what to look for. #1 offender is a solid 1 piece rotor (also picture B) , not only are these heavy, they allow no movement for radial expansion. This allows deformation to happen instantly. Picture c #2 offender is straight vane rotors, yes marketing people like to say curved vane rotors are better because they suck air. That might be the easiest way to explain one benefit of a curved vane rotor. But IMO the curved vanes are a better benefit because the make the rotor stronger and resistant to deformation. #3 Non Floating rotors. It astounds me that people spend $400ea for 2 piece rotors, but they never check to see if they are floating rotors. A floating rotor is as the name applies, it floats. A non-floating does not attach to the hat directly. It is allowed to move radially, this drastically cuts down on coning and drag. A floating rotor is worth it’s weight in gold as it will outlast a fixed rotor 2x one. If you get any drag with a floating rotor your system must have hit a wall. (Floating rotor attachment Picture d)
All I have found this excellent video that has examples of almost everything that can happen with a brake system.
Let’s walk through it.
@ :9 sec-:15sec – the outer edge of the rotor is heating up first, this is bad. We want to see the heat start at the center of the rotor. This is telling me the rotor is coning.
@:24sec further prof of the coning rotor. you can clearly see the outer edge of the rotor has drag marks in it. the cone in the rotor is causing the rotor to dragging. Drag kills straight line speed, ads heat to the system, boiled fluid, kills hubs ect.
@ :35sec you can see the edge of the rotor is changing direction, and starting to cone inwards. Evidence of this is by the very sharp and fine heat band around the rotor. It’s starting to create a wave pattern.
@ :48 sec you can see a very wide band. This tells me that the rotor has cooled and is returning to a normal state. The location of the heat band is on the outter edge. This tells me that although the rotor has cooled the caliper is red hot and starting to flex. That flex is putting brake pressure on the outer ring of the rotor.
@ 1:10, 1:17, 1:28, 1:45, and 2:09. I see no abnormalities and the rotor and brake caliper is working well. Apart from the haze on the outer 1/3 of the rotor, is still dragging when the brakes are not applied.
@2:29 two Heat rings form. This is telling me the rotor is back to Coning and is about to warp. This rotor must be a straight veined unit.
I think someone needs to explain how the size of the master cylinder effects the brake system. Some have touched a few things but I'll attempt to lay it all out here.
A smaller master will give you more braking force and a pedal that will have more travel and allow you to modulate the pedal easier.
A larger master cylinder will give you less braking force (given the same pedal pressure) but it will give you a higher more firm pedal, but your giving up some modulation, since you are moving more fluid with less pedal movement.
Some people (my self included a few years ago) believe that a larger master cylinder will give you more braking force - since it moves more fluid it must allow for more braking force, right? This is dead wrong.
In the world of hydraulics it's pedal force (how hard you push the pedal) x pedal ratio (the lever arm of your brake pedal assembly) / divided by the master cylinder relative area.
So if you went from a 1" to 1 3/8" master you would almost have to push the pedal twice as hard to get the same level of braking force at the caliper!
Now if you have a brake kit that is over sized you may need a larger master or if a nice high and hard pedal is what you're craving go ahead and throw the larger master on, but if you want braking force stick with stock.
I have replaced a few bad master cylinders over the years because people had spongy pedals or heard a "wooshing" sound at the master when they hit the brakes. Which meant there is a good chance that fluid is pushing past the seal inside your your master separating the front and rear circuits inside the master or recirculating back into the reservoir.
Last edited by 96CollectorSport; 07-13-2015 at 10:57 AM.
I think someone needs to explain how the size of the master cylinder effects the brake system. Some have touched a few things but I'll attempt to lay it all out here.
A smaller master will give you more braking force as well as pedal that will give you more travel and allow you to modulate the pedal easier.
A larger master cylinder will give you less braking force (given the same pedal pressure) but it will give you a higher more firm pedal, but your giving up some modulation, since you are moving more fluid with less pedal movement.
Some people (my self included a few years ago) believe that a larger master cylinder will give you more braking force - since it moves more fluid it must allow for more braking force. This is dead wrong.
In the world of hydraulics it's pedal force (how hard you push the pedal) x pedal ratio (the lever arm of your brake pedal assembly) / divided by the master cylinder relative area.
So if you went from a 1" to 1 3/8" master you would almost have to push the pedal twice as hard to get the same level of braking force at the caliper!
Now if you have a brake kit that is over sized you may need a larger master or if a nice high and hard pedal is what you're craving go ahead and throw the larger master on, but if you want braking force stick with stock.
I have replaced a few bad master cylinders over the years because people had spongy pedals or heard a "wooshing" sound at the master when they hit the brakes. Which meant there is a good chance that fluid is pushing past the seal inside your your master separating the front and rear circuits inside the master or recirculating back into the reservoir.
Don't trust a brake calculator that doesn't take center of gravity into effect. the cross weight and center of gravity will play more of a roll then tire size will.
i'll rehash my caliper discussion from another thread. it covered hydrolic advantage a little more thorough.
FYI
Piston count means nothing. how many pistons you have means 0.00000 to performance. Going form a 1 piston to a 6 piston will not increase your performance AT ALL!! there is a knee in the graph, but generally speaking the more pistons you have the worse a caliper gets. a caliper needs not to be judged by piston count but instead by rigidity, and piston size.
Pistons,
Everyone remembers the digital Camera war of Megapixels. the marking men said this camera has 4 pixels and that's better then 3 pixel. when in fact the amount of pixels it had meant nothing. it was a trick to get people to buy the next model. Brake manufactures have done the same with piston counts. They say "OH look a 8 piston!! buy now!!". The fact of the matter is this - the more pistons you have the worse your fluid will travel to all the pistons consistently. We found that the ideal number of pistons to have in a fixed caliper is 4. 4 pistons push evenly on all edges of a pad, and it can still keep consistent fluid pressure. we have also found that more pistons you have above 4 the less consistent a caliper becomes with fluid delivery to each piston. The only time we've seen 6 pistons be better performers then 4 pistons was is the size of a caliper was an issue. in NASCAR, we use 6 piston caliper to clear that tiny 15" wheels. for 90% of the applications out there we don't need to worry about that. so that 8 piston caliper you've been eyeing... run away from it.
Rigidity
a caliper is only as good as how stiff it is. a solid caliper can be felt in the peddle. time after time the peddle can be relied on to be in the exact same spot. If your reading this and not agreeing then your system is in desperate need of improvement. flex of the caliper is the same as the flex in the lines. people go crazy with stainless brake lines. they do this because it improves peddle feel. Unknowingly, they swap the stainless lines onto a caliper that flexes. the stiffer a caliper is the less it will flex. A flexing caliper requires the pistons to travel further to apply the same amount of pressure. the extra travel in the pistons means the pistons are moving further out of the bore. they will need to travel further back into the caliper to be able to remove pad pressure off the rotor surface. A caliper, let me restate that. a Good caliper has square O rings. these square O rings retract the pistons only so much. for example lets say 1mm. if a caliper flexes and the pistons need to travel 1.1mm that means the O rings cannot retract the piston, and you will still have residual brake pressure on the rotor. that residual pressure is creates drag. The Drag is acting like the brakes are still on. imagine you heading down the back straight. how much more MPH do you think we can get if your brakes where off.
Found this nice video From stop tech on how flexy Factory calipers are. before you start knocking the results member that this test is at room temperature, with a hand pump. Normal Brake system will see 1200-1500psi. at a race a calipers can see >600*
Piston Size.
we have gone over this before, so i wont go too in depth about master cylinder ratios. i will focus on the pistons themselves. Everyone overlooks the piston size. so your calipers are a 12 piston.. your pistons must be the size of dimes. that's not a good situation. When looking at a fixed caliper we want to see 4 large pistons. this gives us the best hydraulic advantage.
Don't trust a brake calculator that doesn't take center of gravity into effect. the cross weight and center of gravity will play more of a roll then tire size will.
That is very true yes. It factors a common size tire "behind the scenes" and calculates actual tire torque. While not terribly in depth it's a quick method of doing some base comparison.
If you want to factor the Cg, wheel base, corner weights and such move to the more indepth DUAL MC CALC.
*To which you can make a single by populating the front and rear to the same spec and centering your balance bar to 'zero'.
I do like those 12 pots for looks tho! And hey; they have to be 2X as good as a six right?
Last edited by Todd TCE; 07-13-2015 at 01:08 PM.
Reason: poor choice of wording
i'll rehash my caliper discussion from another thread. it covered hydrolic advantage a little more thorough.
FYI
Piston count means nothing. how many pistons you have means 0.00000 to performance. Going form a 1 piston to a 6 piston will not increase your performance AT ALL!! there is a knee in the graph, but generally speaking the more pistons you have the worse a caliper gets. a caliper needs not to be judged by piston count but instead by rigidity, and piston size.
Pistons,
Everyone remembers the digital Camera war of Megapixels. the marking men said this camera has 4 pixels and that's better then 3 pixel. when in fact the amount of pixels it had meant nothing. it was a trick to get people to buy the next model. Brake manufactures have done the same with piston counts. They say "OH look a 8 piston!! buy now!!". The fact of the matter is this - the more pistons you have the worse your fluid will travel to all the pistons consistently. We found that the ideal number of pistons to have in a fixed caliper is 4. 4 pistons push evenly on all edges of a pad, and it can still keep consistent fluid pressure. we have also found that more pistons you have above 4 the less consistent a caliper becomes with fluid delivery to each piston. The only time we've seen 6 pistons be better performers then 4 pistons was is the size of a caliper was an issue. in NASCAR, we use 6 piston caliper to clear that tiny 15" wheels. for 90% of the applications out there we don't need to worry about that. so that 8 piston caliper you've been eyeing... run away from it.
Johnny thanks for the great info. For the C6 Z06 I have noticed the aftermarket BBK manufacturers (AP, StopTech, Wilwood) all make and recommend the 6 piston calipers and not 4 piston. Ive have spoken to them recently on the phone and they all recommended to have their 6 piston setups.
Is this just marketing/sales they are pushing? Or why aren't any of these companies making the 4 piston setups as you mention that are superior?
Johnny thanks for the great info. For the C6 Z06 I have noticed the aftermarket BBK manufacturers (AP, StopTech, Wilwood) all make and recommend the 6 piston calipers and not 4 piston. Ive have spoken to them recently on the phone and they all recommended to have their 6 piston setups.
Is this just marketing/sales they are pushing? Or why aren't any of these companies making the 4 piston setups as you mention that are superior?
Thanks for the advice!
Is it possible/likely that these major, well respected, top of the food chain brake companies are just "making what the stupid consumer want's to buy" in spite of brake engineering reality?
Is it possible/likely that these major, well respected, top of the food chain brake companies are just "making what the stupid consumer want's to buy" in spite of brake engineering reality?
I've talked to several brake companies and guys "in the know" and especially in the case of the C6Z a 4 piston front kit would be seen as a "down grade".
Although it does make me wonder if 4 piston calipers are better then why do the Pratt and Miller Corvettes run 6 piston in the front and the rear?
reading through this it would seem to me that it would have to do with size. May just not be able to manufacture the right caliper with 4 pistons the right size for our cars so best option is 6. I don't know just guessing here.
I've talked to several brake companies and guys "in the know" and especially in the case of the C6Z a 4 piston front kit would be seen as a "down grade".
Although it does make me wonder if 4 piston calipers are better then why do the Pratt and Miller Corvettes run 6 piston in the front and the rear?
i said a caliper needs to be judged by it's rigidity and not by it's piston count. ask your "guys in the know" why a 4 piston is a downgrade. they won't have an answer, if they do have an answer of "larger piston area" then that is BS. You can get equal piston area from both sets.
PFC makes a 4 piston corvette BBK that comes with full floating rotors. I would avoid that kit simply because the pads are cuffing expensive. My point is get piston count out of your minds, rigidity is the important factor, and avoid anything that has more then 6 pistons.
The Corvette racing cars (I assume) are running 6 pistons for size restraints. you would need to ask Jeff@essex on that one.
No way trying to step on toes here but to get back to the root of the qty question I'l toss in my .02.
Two main reasons:
1. Sex sells. ...moving on...
2. Packaging.
As rotors have grown larger the need for larger caliper bodies to fit them has also. When that happens the pads have gotten longer (more cubic inches for the track guys) and thus the force loads working on that longer pad need to be spread out as well.
Imagine that 12 pot caliper above with a 7420 pad inside it (not that it would fit say a 15" rotor well anyhow) and only two pistons per pad. A massive amount of wasted space! With that monster comes perhaps an 8" long pad. In order to balance out the pressure (ideally) that same 4 pot area must now be spread from 2 to 6 pistons. Thus each piston is far smaller. The net force remains the same only on a larger pad.
I won't venture deep in to the caliper design aspect of things. I'm not a caliper engineer and I'm smart enough not to try do create a huge debate with Johnny C in any way. Clearly his depth of field greater than mine. But I hope that info gives some food for thought.
Last edited by Todd TCE; 07-14-2015 at 11:25 AM.
Reason: removed signature again for peace
07-12-2015, 11:09 AM
