mod de master a brake

[marc87]

salut tout le monde

j aimerais juste savoir si ca change de quoi si je remplace mon master a brake pour quelque chose de plus gros genre a metons sti ... si sa fite , j ai vue sur quelque sit qui a ceux de gd qui fite mais ca fait tu reelement un diference et pk ?

j ai presentement des 4 pot en avant et des 2 pot arrriere plus ligne en stainless au 4 coins

merci d avance

[Pykar]

hou, curieux de la réponse moi aussi

En passant, double post

[homer09]

dans le GD c'est tout pareille, RS à STI c'est la meme chose.

mais en effet, il me semble que c'est un upgrade pour une GC.

[marc87]

double post? je doit etre aveugle lol mais bon

[Pykar]

pas ici, directement dans la section Freins,
Tu as posté 2x la même chose

Présentement ton 2e posts est le 6e en liste

[marc87]

corriger lol merci

back to topic now

hehe

[jefars]

dans le GD c'est tout pareille, RS à STI c'est la meme chose.

mais en effet, il me semble que c'est un upgrade pour une GC.

oui cest une de mes modif pour lundi, merci homer

[UGCspawn]

si tu met un single stage vs un double stage, tu va sentir une bonne différence. Ton autre option est de changer le cylindre. Il y a deux grandeur dans le subaru (ABS). c,est le feeling qui va changer, pas une amélioration coté freins. il y a un bon post la-dessus qui flotte sur nasioc et que je ne trouve pas, mais qui vaut la peine de lire.

[jefars]

ici: pour le M/C
http://forums.nasioc.com/forums/showthr ... ight=brake

++ info sur le travel:

Factors that contribute to lost brake pedal travel:


THIS IS JUST GENERIC INFO, NOT FOR ANY SPECIFIC VEHICLE.



Just some of my experience from being an automotive brake engineer in Michigan for awhile.

First some quick definitions: Brake Pedal ratio is the measurement of how much mechanical assistance you are getting from the pedal. Example; an ratio of 4.1 will give you 41 pounds at the booster input rod for a 10 pound load at the pedal itself.

Dead or lost travel is how much pedal stoke is required before you actually start stopping.

Dead Travel or Lost travel and overall poor pedal feel is made up of the following:
[(travel as measured at the brake service pedal assembly pin (where the booster connects)]
(imagine traveling from the pedal through the brake system to the rotor, all lost travel must be multiplied by whatever your brake pedal ratio is.)

1. Tolerance between brake pedal pin and booster input rod. This can be quite a bit for systems that use a pin mounted brake light switch. If you do have such a switch do not remove it or take up the slack as your brake lights will be on all the time. If you don't have a pin mounted switch just get a tighter bushing. If you do..you s**t out of luck.
* will be felt during first few mm of travel

2. Slack in the brake pedal assembly itself. To see how good or bad yours are, with the car off pump the brakes until hard (2-3 pumps) and then grap the pedal with your hands and see how much it moves around.
* will be felt through first few mm of travel (I hope)

3. Dash flex. This can range dramatically from vehicle model to vehicle model. Not much you can do about this.
*felt during medium and high decelerations stops on most cars, on Fords dashes flex with the breeze

4. Lost travel in booster. This is designed to be there to allow for booster expansion due to climate and use over time. Only adds half a mm (multilplied by the pedal ratio).
*felt only in the first few mm of travel

5. Flex of booster shell. Can be a real problem on some designs. All you can do is try and brace the booster or replace with a better product.
*felt on medium and high deceleration stops

6. Design tolerances in the Master Cylinder. Varies creately from one to another. Simply, if you want less lost travel in the TMC (tandem master cylinder), you have to pay for a more expensive one. A minimum lost travel of about 1-1.5mm is required for proper and safe operation. However, I've seen some with double that. (again multiplied by the pedal ratio)
*felt duiring first 10mm or so of pedal travel

7. The brake tubes and ABS unit. Maybe .0000001mm here. Don't worry about it.

8. Brake hoses. Get steel braided ones, there worth it. Rubber hoses flex quite a bit even under low pressure.
*felt almost all the time

9. Brake Caliper Piston Roll Back. This is usually the worst offender. Only way to get rid of these is get better calipers. Roll back is how far the piston moves away from the rotor when pressure is released. The bigger the gap, the more you have to push on the pedal to get contact.

10. Caliper Defelection. The caliper actually flexing under pressure, like 9 you can only improve this with better calipers.
*felt during medium and high deceleration stops

11. Brake pad backing plate. If this is flimsy it will flex and not allow a good contact between the rotor and pad forcing you to apply more pressure and therefore more pedal travel. Fixed by replacing pads with higher quality ones.
*felt most of the time

12. Brake pad material itself. If the material is low density it will compress like a sponge. And if it's a low mu (friction) pad it will require more pressure and therefore more pedal travel.
*felt all the time

13. Rare, but a problem on really cheap brake pads: The bonding process used to bond the brake pad material to the backing plate. A poor process will cause the material to "squirm" around.

Well those are the biggy, but not the biggest. The biggest is AIR in the system.. Before you do anything else do a really good and thorough brake bleed. And only use the fluid it says to use on the cap, DOT 3 or DOT 4 or whatever.

How I would go about improving a system:
1. Bleed system
2. High quality pads
3. Get steel brake hoses
4. New fixed calipers from a know manufacturer
5. Some bracing for the actuation unit (booster/ master cylinder/ pedal)

Also, changing the brake pedal assembly to one with a lower ratio. Remember all lost travel is multiplied by the pedal ratio, the lower the ratio the less dead travel at the pedal pad. This also firms up the pedal as your getting less mechanical assistance. Just be careful, because if you brake booster fails it will take more force on the pedal to come to a stop. Minimum pedal ratio is calculated using NHTSA FMVSS 135 which states the maximum force required to stop a vehicle in a certain distance when the booster fails.

Pedal feel can also be "tuned" with a different booster. I will not get technical, but basically the booster sets the Force-Force curve (Force into the booster vs. the force out). How this curve looks will dictate pedal feel (assuming all else equal). A F-F curve has certain points that are important, the 2-stage, cut-in, boost ratio and the run-out.

2-stage is what sets the intial point of boost (when it kicks in)
cut-in is what sets how much initial force
boost ratio is just as it sounds, it sets how much assit you get
run-out is the maximum assist

By lowering the 2-stage and increasing the cut-in you get a better intial bite sooner. Just have to be careful you don't go overboard and have the driver eat the steering wheel at every stop light (like an '80s Audi).

Difference between Feel and Performance
Just some more stuff:

I want to make it clear there is a difference between making a brake system feel better and actually perform better.

The stopping distance of a car is not necessarily directly related to the feel. A poor feeling brake system can have very good performance, i.e. Jaguar. While a great feeling system can have lousy performance, i.e. Ford Focus

The only way to decrease braking distances is to create more heat through friction and conduct that heat more efficiently.

Basically, you need a bigger contact area between the rotor and pad (bigger pads and rotors) with the best contact patch possible between the two. Also higher friction levels with higher mu brake pads.

And most importantly.........REALLY GOOD TIRES!

And you need a way to get rid of that heat at a faster rate. More rotor mass and/or better conduction (vented, etc...).


How a car stops is simple, it takes Kinetic Energy (energy created by motion) and transfers it to Heat (infrared) Energy. It does this by the mechanism of friction.

KE=1/2 the mass of the vehicle multplied by the square of it's velocity

Stopping distance is determined by the rate of KE to IE transfer, or also know as WORK.

Simply, to stop sooner you need to transfer Kinetic Energy into Heat Energy faster.

There are no other tricks...you need higher levels of friction and ways to dissipate the heat quicker (you can also get more massive rotors which are capable of absorbing more heat).


The big things to do to get shoter stopping distance:

1. Best Tires for the conditions (use common sense here, no Pilots in Feb in Alaska)
2. Higher Firiction Brake Pads
3. Bigger rotors with better heat conduction properties or better heat absorbtion properties

That's it!!!!!!!

The small things you can do that give you that extra advantage:

1. LOSE WEIGHT (the car I mean), less mass, less KE

2. Minimize rotational interia of wheels/tires. Get lighter wheels and tires (all else being equal). Note: the farther away from the center of rotation the mass is the great the interia, so a 17" wheel will have greater interia than a 16" all else being equal.

3. Try and balance out the braking, if the rears can do more work it spreads out the work. Less weight transfer to the front [edited 4/5] BY MOVING THE BATTERY TO THE TRUNK, stuff like that.

4. Calipers with more pistons and more piston area, this gets you that better contact between rotor and pad.

5. Pratice! Get to know how your system works so you can best utilize it.

6. Don't drive to fast, remember it the square of the velocity. The amount of KE increase from 40KPH to 80KPH is not 200%, but 400%.

[jefars]

question

The question for all you brake engineers is: what size master cylinders (F & R) would you recommend? Please support your answer with at least a little bit of math.

Here are the parameters:

Brake rotor diameter: 260mm F, 220mm R
Effective radius (to center of pad): 110mm F, 95mm R
Caliper type: 4 pot (2 per side) F, 2 pot (1 per side) R
Caliper piston area: 31.1cm^2 F, 15.6cm^2 R
Pedal ratio: 5.5:1
Vehicle weight: 1500lbs
Desired braking force ratio: 80% F, 20% R
No booster--all manual.

I think that's all you should need--let me know if I missed something.

Thanks!

rep:

There is no front/rear. For master cylinder all you need to worry about is the caliper piston sizes and pedal ratio. The master cylinder (MC) is only there to provide volume for the calipers.


The brake bias comes from your prop valve and rotor/caliper sizing.


You can use the largest MC you can find, there is no such think as too big, just to small. The above are the minimum you will need to even be close to decent.

The larger the bore of the MC the less stroke you will need, but the softer the pedal will be. If you can live with not so good pedal feel then get a 26.99mm MC, which is what is used on most large trucks (Like Ford F-150).

Here is how to calculate mechanical advantage:

Area of MC * pedal ratio = M
Area of front piston= N

ME= M/N = larger is less effort


25.4mm (1 inch) MC gets you close to a 1:1 so for every 100lbs at the pedal you get a 100 pounds at the caliper.

Your racer only weighs 1500 pounds you don't need much.

Well what I wrote above still holds. Just now your splitting the car in half.

Basically look at the rears separate from the fronts.

So you would look at the MC size for the fronts just by looking at the front pistons.

Same for the rears

The only thing that can be tuned is feel. You can go to a larger bore for a shorter pedal stroke or to a smaller bore with a longer stroke but firmer feel.


By the way all modern MC are TMC, tandem master cylinder, which is a dual MC in one casting. Of course this means both chambers need to be the same diameter.





It's hard to tell you exactly what size because I don't know your feel preferences. Personally for racing I would rather have a short stroke, low effort pedal (large bore/short stroke) for long distance racing and the firm, longer stroke for sprints( small bore/long stroke). Why? Because on long races my leg will cramp up!


Geez..that thing costs! You must be serious about your motorsports!


This can help you get close to "ideal"

Stopping Force = pedal force * brake pad coefficient of friction * mechanical force ratio * (1/radius of the tire) * brake rotor effective radius

stopping force = weight of car * longitudal coefficient of friction of tires

mechanical force ratio is what you are looking for.

This ratio should get you right to lock up.

Take that ratio and divide it by the pedal ratio.

This is the ratio of mastercylinder bore area and caliper piston bore area.

So say a 4:1 then for a 30cm^2 caliper piston you want a 7.5cm^2 MC or ~28mm bore MC.

For the fronts use the total mass of the car, for the rears use the weight just over that axle. This ensures you get max braking power without locking up the rear all the time.

Front - Rear Bias

personally I'd concentrate on the fronts since you only want 20% rear bais but here you go:

Front Force = weight front + total weight * tire friction * height of CG * (1/wheel base)

Rear Force is the same except substitute weight front with weight rear and change the + to a -

The ratio Front/Rear should be used to get the Front Braking Force and Rear Braking Force percentages.

I.E. For a Front/Rear = 3:1 then the use 75% of the Stopping Force for to get the diameter of the MC for the front calipers.

Summary of Equations:
(for ease and consistency try and use meters and kg)

1.
stopping force = weight of car * longitudal coefficient of friction of tires


2.
Stopping Force = pedal force * brake pad coefficient of friction * mechanical force ratio * (1/radius of the tire) * brake rotor effective radius

.....solve for mechanical force ratio


3.
Front Force = weight front + total weight * tire friction * height of CG * (1/wheel base)

4.
Rear Force = weight rear - total weight * tire friction * height of CG * (1/wheel base)


5.
% front = Front Force/Stopping Force


6.
% Rear = Rear Force/Stopping Force

7.
mechanical force ratio front = mechanical force ratio * %front
mechanical force ratio rear = mechanical force ratio * %rear


8.
Take that ratio and divide it by the pedal ratio.

This is the ratio of mastercylinder bore area and caliper piston bore area.

So say a 4:1 then for a 30cm^2 caliper piston you want a 7.5cm^2 MC or ~28mm bore MC.

OK, so just using the fronts--as if the fronts are stopping 100% of the weight (which isn't far off), here's what I get:


Code:
Pedal pressure 100 lbs
Brake pad Cf 0.5
Effective disc radius 0.36 feet
1/tire radius 1.07

All up weight 1500
Tire Cf 1.2
Stopping Force 1800

Force ratio 93:1
Pedal ratio 6:1
Caliper to MC area 15.6
Caliper piston size 44.5mm
Caliper piston area 3111mm^2
x two calipers 6221mm^2
MC area needed 399mm^2
MC diameter 23mmSo I should be fine with a standard 7/8" MC

Quote:
Originally posted by Jon Bogert
Mike just to clarify, I think you got something reversed:

A larger MC results in...
> less pedal travel
> a firmer pedal
> less hydraulic advantage

A smaller MC results in...
> more pedal travel
> a softer pedal
> more hydraulic advantage

Larger caliper piston area results in...
> more pedal travel
> a softer pedal
> more hydraulic advantage

Smaller caliper piston area results in...
> less pedal travel
> a firmer pedal
> less hydraulic advantage

Say you have 2 tubes, one is 1 sq in the other 2 sq in. Tubes are filled with fluid with a piston inside. You apply 100 lbs to the piston.

The 1 sq in tubes will produce 100PSI at the other end while the 2 sq in tube will produce 50PSI at the other end. Which is all that's coming back at you. So your displacing the same volume but building less pressure with the larger MC which is why you feel less effort at the pedal.

It's similiar to flow through a tube, the larger the tube the less effort. Like an exhaust system, larger tubing and less back pressure.

So everything else you have is correct, but the effort part for the MC.

To put in non braking terms:

The larger the bore of a tube the less back pressure and the less hydraulic pressure at the other end. So with a larger bore you flow more, more easily, but get less force at the other end.


Unfortunately with many cars that have large volume requirements (to ensure full travel of the caliper piston) your sometimes forced to go with a large bore MC otherwise the pedal travel is just too long (imagine a MC in your SUV that's 80mm long, packaging and casting nightmare).

Quote:
Originally posted by Jon Bogert
OK look at it this way...

If you use a larger MC, but change nothing else, the ratio of the MC area to the caliper piston area will increase. If it's 1:70 and you double the size (area) of the MC, it becomes 1:35. So to produce equivalent stopping force, you have to push twice as hard.

Take this example to its limits--with equal area MC area and caliper piston area--and you'd have to push pretty damn hard to generate that 1800lbs of force!

Yes your right.

I did get myself mixed up. In my own mind confused effort and feedback. Hey I am a little sick so I'm sure the beer had nothing to do with it.

Sorry I shouldn't have used the term effort. I forget that not everyone thinks the same way I do.


With a larger MC bore you will have less "feedback" Think of it in the same terms are air in the system, requires more effort to stop and gives a mushy pedal (of course air also increase travel).

I should have put it in terms of feedback. A larger bore MC gives you less feedback.

SUVS and full-size pickups are great examples. Even when their brake sizing at the corners is fine they still require a hefty push on the pedal, but the pedal feels like a bag of marshmellows because of the large bore MC they have to get the required volume.

In pedal feel there's:

Effort vs. Travel
Travel vs. deceleration
Effort vs. deceleration
Work vs. deceleration


I hang my head in shame!

[hellbent]

assez simple

master cyclindre de svx avec le brake booster single stage impreza. Il y a deux model (2 port 4 port) 4 port c non abs et 2 port c abs. le master est 1 /16 vs 15/16 que on a stock.

http://www.northursalia.com/modificatio ... oster.html

le p/n du booster est bon mais il te faut le master de svx. Ya pomal de gars sur rs25 avec se setup la et c a1. Sur ma blanche je fait sa cette ete + abs delete (ugh).

[marc87]

merci je vais checker ca hehe

[jefars]

j'ai jamais regarder cela...

Hier j'arrive pour installer mon Nouveau M/C 1+1/16 Il est 2port

et le mien est 4 port (mon 15/16)...

maintenant ca me prend un 4port 1+1/16, il se fait plus gros en 4port ?

Merci

SVX... Photo, Il a d'autre model avec de 4port 1+1/16 ?


Rockauto: $151.99
RAYBESTOS Part # MC390207 {Professional Grade Bore Size=1 1/16" Number of Ports=4 Primary Outlet Size=M10x1}
Except Antilock Brakes (Only 3 Remaining)