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Old 03-15-2002, 03:03 PM   #1
8Complex

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Default Brake Fluid FAQ & Pedal Feel Info (the reference post)

Some documentation for the board. I needed to know a few things, just figure I'd share the welth of information as I gather it myself.

PS - If anyone has any additional information on different fluids, etc, please reply about it and I will add it up to this main post. Occasionally I will delete replies to get the overall size of the post down, but make sure to check the bottom "Thanks" section for credits.

Common Brake Fluid Boiling Points

Code:
Fluid Brand          || Wet Boiling Point || Dry Boiling Point
Castrol SRF          ||       518F       ||       590F
Earl's HyperTemp 421 ||       421F       ||       585F
Motul 600            ||       420F       ||       593F
AP-600               ||       410F       ||       572F
Neosynthetic 610     ||       421F       ||       610F
ATE-Super Blue       ||       392F       ||       536F
Valvoline            ||       333F       ||       513F
Castrol LMA          ||       311F       ||       446F
Earl's HyperTemp 300 ||       300F       ||       568F
Ford HD              ||       290F       ||       550F
Wilwood 570          ||       284F       ||       570F
PFC-Z rated          ||       284F       ||       550F
AP-550               ||       284F       ||       550F
(plagarism at it's best )
All brake fluids absorb moisture, some faster than others (except silicone which is not recommended for anti-lock brake systems). Castrol SRF resists moisture contamination (non-hygroscopic) more than any other fluid we tested, therefore change intervals can be greatly extended. This reduces the effective cost over a season of racing. Many drivers say that they can run the same fluid all year long with only bleeding off the fluid in the calipers for each event. This way a can or two will last all year. Other fluids (hygroscopic type) require additional flushing of the system for each track event to maintain the lowest percentage of moisture and the highest boiling point.

FYI - The Castrol SRF is around $77/container versus $10-15/container for the rest.

Silicone Brake Fluids
(more plagarism)
Fluids containing Silicone are generally used in military type vehicles and because Silicone based fluids will not damage painted surfaces they are also somewhat common in show cars.

Silicone-based fluids are regarded as DOT 5 fluids. They are highly compressible and can give the driver a feeling of a spongy pedal. The higher the brake system temperature the more the compressibility of the fluid and this increases the feeling of a spongy pedal.

Silicone based fluids are non-hygroscopic meaning that they will not absorb or mix with water. When water is present in the brake system it will create a water/fluid/water/fluid situation. Because water boils at approximately 212 F, the ability of the brake system to operate correctly decreases, and the steam created from boiling water adds air to the system. It is important to remember that water may be present in any brake system. Therefore silicone brake fluid lacks the ability to deal with moisture and will dramatically decrease a brake systems performance.

MINIMAL boiling points for these specifications are as follows:

Code:
  DOT # || Dry Boiling Point || Wet Boiling Point 
DOT 3   ||      401F        ||       284F
DOT 4   ||      446F        ||       311F
DOT 5   ||      500F        ||       356F
DOT 5.1 ||      518F        ||       375F
Poly Glycol Ether Based Brake Fluids
(more plagarism)
Fluids containing Poly glycol ethers are regarded as DOT 3, 4, and DOT 5.1. These type fluids are hygroscopic meaning they have an ability to mix with water and still perform adequately. However, water will drastically reduce the boiling point of fluid. In a passenger car this is not an issue. In a racecar it is a major issue because as the boiling point decreases the performance ability of the fluid also decreases.

Poly glycol type fluids are 2 times less compressible than silicone type fluids, even when heated. Less compressibility of brake fluid will increase pedal feel. Changing fluid on a regular basis will greatly increase the performance of the brake system.

FLUID SPECIFICATIONS All brake fluids must meet federal standard #116. Under this standard is three Department of Transportation (DOT) minimal specifications for brake fluid. They are DOT 3, DOT 4, and DOT 5.1 (for fluids based with Polyalkylene Glycol Ether) and DOT 5 (for Silicone based fluids).

Wet vs. Dry Boiling Point
(more plagarism)
WET BOILING POINT - The minimum temperatures that brake fluids will begin to boil when the brake system contains 3% water by volume of the system.

DRY BOILING POINT - The temperatures that brake fluid will boil with no water present in the system.

How does water get in there?
(more plagarism)
Water/moisture can be found in nearly all brake systems. Moisture enters the brake system in several ways. One of the more common ways is from using old or pre-opened fluid. Keep in mind, that brake fluid draws in moisture from the surrounding air. Tightly sealing brake fluid bottles and not storing them for long periods of time will help keep moisture out. When changing or bleeding brake fluid always replace master cylinder caps as soon as possible to prevent moisture from entering into the master cylinder. Condensation, (small moisture droplets) can form in lines and calipers. As caliper and line temperatures heat up and then cool repeatedly, condensation occurs, leaving behind an increase in moisture/water. Over time the moisture becomes trapped in the internal sections of calipers, lines, master cylinders, etc. When this water reaches 212 F the water turns to steam. Many times air in the brake system is a result of water that has turned to steam. The build up of steam will create air pressure in the system, sometimes to the point that enough pressure is created to push caliper pistons into the brake pad. This will create brake drag as the rotor and pads make contact and can also create more heat in the system. Diffusion is another way in that water/moisture may enter the system.

Diffusion occurs when over time moisture enters through rubber brake hoses. The use of hoses made from EPDM materials (Ethlene-Propylene-Diene-Materials) will reduce the amount of diffusion OR use steel braided brake hose with a non-rubber sleeve (usually Teflon) to greatly reduce the diffusion process.

DOT what?
(even more plagarism)
DOT: Acronym for "Department of Transportation" -- an American federal agency or "Department of Transport" -- a British agency

DOT 3: This brake fluid has a glycol base. It is clear or light amber in color. Its dry boiling point is 401 minimum and wet boiling point of 284 minimum. It will absorb 1 to 2 percent of water per year depending on climate and operating conditions. It is used in most domestic cars and light trucks in normal driving. It does not require cleaning the system and it can be mixed with DOT 4 and DOT 5.1 without damage to the system. The problem with it is that it absorbs moisture out of the air and thereby reduces its boiling point. It can also damage the paint on a vehicle.

DOT 4: This brake fluid has a borate ester base. It is clear or light amber in color. Its dry boiling point is 446 minimum and wet boiling point of 311 minimum. It is used in many European cars; also for vehicles in high-altitude, towing, or high-speed braking situations, or ABS systems. It does not require cleaning the system and it can be mixed with DOT 3 without damage to the system. The problem with it is that it absorbs moisture out of the air and thereby reduces its boiling point. It can also damage the paint on a vehicle.

DOT 5: This brake fluid generally has a silicone base. It is violet in color. Its dry boiling point is 500 minimum and has no wet boiling point in federal DOT 5 specifications. It is used in heavy brake applications, and good for weekend, antique, or collector cars that sit for long periods and are never driven far. It does not mix with DOT 3, DOT 4, or DOT 5.1. It will not absorb water and will not damage the paint on a vehicle. It is also compatible with most rubber formulations. The problem with it is that it may easily get air bubbles into the system which are nearly impossible to remove, giving poor pedal feel. It is unsuitable for racing due to compressibility under high temperatures. If as little as one drop of water enters the fluid, severe localized corrosion, freezing, or gassing may occur. This can happen because water is heavier and not mixable with silicone fluids. It is unsuitable for ABS.

DOT 5.1: This brake fluid has a borate ester base. It is clear or light amber in color. Its dry boiling point is 500 minimum and wet boiling point of 356 minimum. It is used in severe-duty vehicles such as fleets and delivery trucks; towing vehicles, and race cars. It can be mixed with DOT 3 or DOT 4 without damage to the system. It maintains higher boiling point than DOT 3 or DOT 4 fluids due to its higher borate ester content. It is excellent for severe duty applications. The problem with it is that it costs more than other fluids and there is limited availability. It also absorbs moisture out of the air and thereby reduces its boiling point. It can also damage the paint on a vehicle.

What causes a mushy pedal?
(some more plagarism)
DOT 5 fluid is not hygroscopic, so as moisture enters the system, it is not absorbed by the fluid, and results in beads of moisture moving through the brake line, collecting in the calipers. It is not uncommon to have caliper temperatures exceed 200 F, and at 212 F, this collected moisture will boil causing vapor lock and system failure. Additionally, DOT 5 fluid is highly compressible due to aeration and foaming under normal braking conditions, providing a spongy brake feel.

Also, many locations across the internet point towards the stock rubber lines as a source of spongy feeling. I cannot comment on this personally as I have upgraded both the fluids and lines at the same time, though I'm sure they both help pedal feel when upgraded.

Other good links:
http://www.shotimes.com/SHO3brakefluid.html

Special thanks to these people for contributions!
zzyzx - For the additional good info link. Also for the additional reply with information below on spongy brake feel.
zemmo - For the Neosynthetic fluid boiling points.
Jaxx - For inspiring a more comprehensive DOT # explanation.
Marquis - For pointing out the hydroscopic vs. hygroscopic errors.
Concillian - For the code tag hint (hence everything nice and aligned now).
shifterkartracer - For asking how much fluid it takes to fill the Impreza systems.
JamesC - For correcting my Motul 600 boiling points.
scotty305 - For inspiring adding a section on brake feel (of which zzyzx also contributed to heavily in a reply below).
romanom - For the extra-long and very informative post about the mechanics of brake feel.
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Last edited by 8Complex; 04-05-2002 at 11:10 AM.
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Old 03-18-2002, 11:25 AM   #2
8Complex

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Default

If you look at the boiling points and look at the DOT minimum boiling points (in the second chart) you can pretty much figure out which are which. All the DOT 3 fluids (Ford HD down) are obviously racing fluids if you look at their high dry boiling temp. and low wet boiling temp.

Most of the other fluids listed are DOT 4 or 5.1 (both have the same base, just different boiling points). I'm fairly sure none of those are DOT 5 since silicone based fluids are generally written off as junk - they're not to be used with ABS systems at all. The only thing that 5.1 is generally used for is show cars that don't want to have paint-harmful brake fluid in their systems... and maybe some people drawn by the voodoo factor of having purple brake fluid.
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Old 03-22-2002, 06:22 PM   #3
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I think the Subaru systems take just under 16oz, so you're best off getting at least 20 so you can bleed some of it out. I got 2 bottles of Motul RBF 600 and I have just about half a bottle left.
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Old 03-29-2002, 01:07 AM   #4
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Here a sympton/solution list based on my personal experience, ordered from most likely to least:

1) Pedal is mushy on cold car before you've warmed things up.

You have air in your system and need to bleed your brakes. This is the most common cause of the mushy pedal feel. Note that on a cold car, where there is no thermal stress, your choice of brake fluid type has no efffect on pedal feel. Fluid (e.g. water) is not compressible, only gas (e.g. air) is.

2) Pedal is mushy after heating up your brakes.

You probably have water in your lines, which turns to gas when above boiling point, and gas compresses, hence the mushy feel. Flush your brake system with new brake fluid.

3) Too much pedal travel.

Pedal travel and height are adjustable. You can decrease the pedal "play" using the lock nut/shaft that pushes into the brake booster. Be careful not to reduce play to the point that your brakes "drag" on the rotors while the pedal is not pressed.

4) Non-linear brake modulation - the dual-stage brake booster.

It's dual stage specifically to provide a non-linear brake pedal feel. It tends to yield a mushy feel at or near the limit. Replace the brake booster and master cylinder with the single stage unit from a non-ABS Impreza L model.

5) The stock rubber brake lines flex.

Replace these with stainless steel brake lines.

6) Brake pads

I threw this in because, depending on your type of brake pads, at the limit response and modulation are greatly affected by your choice of pad type - not just fade resistance. The stock pads are a very good general purpose pad, but do not provde a positive linear feel at the limit.

7) Firewall/pedal assembly flex

The firewall where the pedal assembly will flex under hard braking. MRT makes a bolt-on reinforcement to cut down the flex in the firewall.

Note the above addresses pedal FLEX, not brake FADE, which is a different topic. As you can see, not all the factors the lead to a mushy pedal are necessarily related to your brake fluid.

- Steve

Last edited by zzyzx; 03-29-2002 at 01:18 AM.
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Old 04-03-2002, 04:01 PM   #5
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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).

Last edited by romanom; 04-03-2002 at 06:20 PM.
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Old 04-05-2002, 11:11 AM   #6
8Complex

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Thumbs up

romanom - Great info! Thanks for the post.
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Old 04-08-2002, 05:14 PM   #7
Chin
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Default Bleeding order

8, There was a lot of discussion in the past about what order the brakes should be bled in. I don't remeber what the outcome of all of those discussions was. Do you (or anyone else) have that info? It would be a valuable addition to this.

Christian
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Old 04-08-2002, 05:43 PM   #8
romanom
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Default 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%.

Last edited by romanom; 04-15-2002 at 07:25 PM.
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Old 04-08-2002, 05:44 PM   #9
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Default input on the value of drilled rotors

QUESTION FROM HOTROD:
I have mixed feelings on some of the "quick lets upgrade the brakes" discussions. First of all as you pointed out in your above posts, most consumer brake systems are (on single stops) tire limited. Terrific brakes don't help if the tire is sliding. Assuming the car owner has upgraded to a tire that is good enough that he can now use additional brake power, how much do drilled rotors really help. I have this suspicion that there is a lot more urban legend than fact behind some of the stuff you hear regarding drilled, and slotted brakes.

Is the improvement mostly a more agressive bite on the pad, (ie less peddle effort to get a given level of deceleration, with little change in actual brake force)? Does it actually inprove the total brake force available, by preventing pressure buildup under the pad and ejection of wear particles from under the pad.

I suspect this again is an "it depends" on which brake system you are working with" answer but it is surprising on how little objective information there is out there. It seems the only places you see what appears to be good technical discussion of braking is in sources which are inherently marketing blurbs which I tend to view with suspicion.

This assumes of course that the user has the appropriate pad material for each drilled and non-drilled disk, and street/race usage.



Actually this is a good question..and depends on where you driving. Drilled rotors on a pure street car do 2 things most of the time, look better and decrease weight.

X-drilling is meant to help with heat conduction. Actually drilling holes in the rotor decreases the amount of contact area and in theory will increase brake distances (we're talking mm here).


But how many of you are threshhold braking on the interstate or county roads?

Also, venting built up gases under the pad was a big problem, but pad tech has come so far that it's not something I would worry about (assuming your using race pads for racing). Again it's one of those things that's there but only makes a very minor difference (if any) most of the time. Same thing with slotting, which was developed to vent gases and clean pads.

Things like 2-piece rotors, X-drilling, slotting, crygonics, heat treating are all "at limit" technologies. In other words they only make a noticable difference (if any) at the very limits. If you drive on the street in a manner that actually utilizes these technologies regular your probably dead and not reading this!


I like the idea of x-drilled, 2-piece rotors on my car....BUT for looks and slight weight savings (I think of it the same way as wheel design). Unless I'm talking about a true auto-x or race car, but in racing every little bit counts and I can justify the costs.

IN THEORY The below is true, but like I said above pad tech has come a long way.

Does it actually inprove the total brake force available, by preventing pressure buildup under the pad and ejection of wear particles from under the pad.

And drilling doesn't do anything for pedal feel. Also, drilling and slotting will wear the pad and rotor sooner...don't be fooled by crap that it does the opposite...it don't!

hotrod....brakes are as much art as science..there are just so many different variables involving not only performance but feel and consumer wants it becomes a real pain! To give you an idea, the last program I worked on was a Ford, they increased the overall wheel diameter by 11.25mm, it increased my dead booster (emergency stop with a failed booster) by 7 feet and outside NHTSA's regulations.



What I've done on my cars:

'95 Z28, pads and hoses
'96 BMW 328is, hoses
'00 BMW 328i, hoses
'02 WRX, probably hoses, pads and maybe painting the calipers (for looks, I have open spoke wheels). Possibly lighter rotors depending on how much weight I would save...don't know how much the stock one weigh (and would do it only when it's time for replacement rotors) then again maybe it's just my racing mentality showing.


Just my 2 cents: too many people try to built race cars for the road..it's just a waste of money.

Again, you have to know what you want to get out of your system and where you're going to use it.

In the end if you got the cash it won't hurt, but you get to a point of diminishing returns and you have to wonder! I think the WRX brakes stock are pretty good for street brakes and I belief a good set of high mu pads will be all I need (knowing that wear and dust will be a problem).

The thing with ads is that many times they're true but leave out the circumstances there true under. Decrease braking distance 10ft with our pads....after 20 stops from 150MPH!

Last edited by romanom; 04-15-2002 at 07:26 PM.
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Old 04-08-2002, 05:47 PM   #10
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Default

Here's link to a thread that has some very good questions and responses to what I posted above, especially from hotrod and Concillian.



http://www.i-club.com/forums/showthr...hreadid=168098
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Old 04-08-2002, 06:09 PM   #11
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Default Re: Bleeding order

Quote:
Originally posted by Chin
8, There was a lot of discussion in the past about what order the brakes should be bled in. I don't remeber what the outcome of all of those discussions was. Do you (or anyone else) have that info? It would be a valuable addition to this.

Christian
I was taught to start with the caliper closest to the master cylinder to the farthest from the master cylinder.
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Old 04-09-2002, 02:45 PM   #12
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Quote:
I was taught to start with the caliper closest to the master cylinder to the farthest from the master cylinder.
I was told to do it from the furthest... There was a lot of discussion that indicated another way was the best for the Impreza. I would like to hear what is the best way, and why...

Thanks for the reply, as well.

Christian
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Old 04-09-2002, 10:05 PM   #13
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I was taught to do farthest to closest as well, not sure what difference it really matters, but hey, my brakes are solid as a rock now.
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Old 04-09-2002, 10:47 PM   #14
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I e-mailed a Tech at Ford I used to work with on the proper bleed sequence. Since techs do these all the time and engineers don't I'll take his advice.

This is it:

Doing nearest or most distant doesn't matter. What matters is if the brake system is a diagonal or front-rear system.

quick definition: diagonal means that one circuit in the master cylinder feeds the front driver's side and the rear passenger side. The other circuit the front passenger's and rear driver's. Both circuits are of equal volume. Front-Rear means that one circuit supplies the front calipers, while the other the rear calipers. The Primary circuit (front caliper circuit) is of greater volume.

All you need to do is make sure you do the circuits together. For instance, on most passenger cars it's a diagonal system. So you want to do the driver's front and passenger's rear together, which you do first is not all that important. But he does agree that the tradition is do to the rear first. Or best to get a friend and do both at the same time. And take your time (he told me to make sure I added this).

Same holds true for the Front-Rear systems. Do fronts together and rears together. Usually only trucks, SUVs and very heavy front bias cars (Ford Crown Vic) have a Front-Rear system.


Just FYI- Diagonal is used so that if one circuit fails the vehicle is still stoppable in a stable manner as at least one front and rear wheel is braking and on oppisite sides. Front-Rears are used as heavy, front-bias cars require a lot of volume up front.
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Old 04-10-2002, 10:32 AM   #15
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I don't see how it really matters. Just bleed untill the fluid runs clear/blue/gold. But next time I will do what romanom suggested. So Subarus are left/right circuit?
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Old 04-10-2002, 10:32 AM   #16
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Default Some info on 2-piece brake rotors

II have seen a lot of postings on 2-piece rotors. Some of the information contained in them is correct some is mythical.

Some definitions.

2-Piece rotor: A brake disc rotor that has a separate hat (cap) usually made from a light weight metal. There are two types of common 2-piece street rotors. One uses a bolted hat and the other a pinned hat (also known as a "floating rotor" design).

The bolted type is just what it sounds like. Usually an aluminum hat bolted to a cast iron rotor. The only real benefit of this design is weight savings. However, weight savings tend to be only 10-20%, all else being equal, but with a 50-75% price increase.


The pinned type has usually stainless steel pins that attach the aluminum hat to the rotors. This allows the rotor to "float" on the pins. The great advantage of this design is that it allows the rotor to move freely. When the rotor expands and contracts there is much less chance of binding or distortion. As you can imagine this cuts down on warping and uneven wear (DTV). The disadvantage of this design is really high costs.


As far as better heat conduction, not really. It does help a bit, buts it's not enough to make it worth the extra cost. The nice think about the weight savings is you can get larger rotor with out taking a weight penalty.

[added later] - it amy help keep you wheel bearing cooler.

Last edited by romanom; 04-12-2002 at 06:47 PM.
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Old 04-10-2002, 10:43 AM   #17
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Quote:
Originally posted by HIHO
I don't see how it really matters. Just bleed untill the fluid runs clear/blue/gold. But next time I will do what romanom suggested. So Subarus are left/right circuit?
Yes, the Subarus (at leat the late model ones) are a diagonal system.
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Old 04-10-2002, 03:13 PM   #18
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I was just talking about Ford Heavy Duty brake fluid in a thread here the other day, and last night I found out it no longer exists.

Fortunately, you can still get the same fluid from your Ford dealer, it just isn't sold in 16oz blue metal cans labelled "Ford HD" anymore. Now it is called "Motorcraft High Performance brake fluid", and comes in 12oz plastic bottles. $3 per at "my" Ford dealer ( only thing I've ever bought there ).

Still specifies the same wet and dry boiling points on the container, too.
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Old 04-10-2002, 10:29 PM   #19
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I guess we got different Ford stuff Hillman.

The stuff I got was

Ford Super DOT 4

Min. WET boiling point of 350 deg F (180 deg C) - NO mention as to dry boiling point.

-mykr.
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Old 04-11-2002, 04:30 AM   #20
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Quote:
Originally posted by mykrrrr
I guess we got different Ford stuff Hillman.

The stuff I got was

Ford Super DOT 4

Min. WET boiling point of 350 deg F (180 deg C) - NO mention as to dry boiling point.

-mykr.
most fluids only list the wet boiling point because that is the one that REALLY matters.

jeremy
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Old 04-13-2002, 10:42 AM   #21
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Default Lug Nut Torque

Next Installment:

Most of you already know about this, but some don't and some don't realize how important proper torquing of the lug nuts are.

IF YOU DON'T OWN ONE GO OUT AND BY A TORQUE WRENCH...NOW


Over-torquing of wheel lug nuts is one of the prime causes of brake rotor distortion. This can lead to permanent warping of the rotors, uneven wear of the rotors and pads and lots of brake chatter (NVH).

With todays very stiff alloy wheels, like from BBS, SSR, Volk, etc., when you torque down the lug nuts the wheel mounting surface will force what ever it contact to take it's shape. Which means whatever that surface looks like will be what the rotor looks like.

Get a torque wrench and check the torques on every lug nut and make sure they are within the specs (which you should be able to find in your owner's manual). And make sure that every lug nut is torqued down exactly the same. Even if all 5 on a wheel are within specs, not having all 5 be equal will introduce distortion.

And if you think that your light alloy wheel can't possibly be that stiff, you wrong they are MUCH stiffer than the brake rotor or even the hub.


WORD OF CAUTION: Don't assume that the torque the lugs to the lowest range in the spec is the best. Try and keep it nominal not at the extremes of the range.


Much of the problems with rotor warp, brake chatter, disk thickness variation can be traced back to over-torqued and uneven torqued lug nuts.

After coming back from the shop, get that torque wrench and check the lug nuts yourself.
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Old 04-13-2002, 04:13 PM   #22
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Thumbs up Well Written:

The below was originally posted on Altimas.net Forum by Black200sxSER. I'm putting it here but it's exactly what I've been trying to say, but in a much more articulate manner.


"brakes do not stop a car. the tires do.they are the gripping force that comes into contact with the ground. better tires=better braking..think about that one for awhile.

stock brakes are capable of locking up the tires. they are "adequate" for normal driving. for higher performance applications, (spirited driving, racing)..."BIGGER" brakes are better..due to their ability to take and dissipate heat from the friction created. Also for the larger sizes of caliper that can be used to apply more clamping force, which generates more heat, which larger calipers do. the larger rotors can take MORE of this heat..due to size, and dissipate it better due to more mass.

cross drilled rotors are more for looks than for performance due to todays technology in pad materials. look at any form of racing, and they are running huge regular rotors..or in some instances slotted rotors (ex: Rally keeping pads cleaner) Slotted are somewhat better due to the ability to self clean the pad. But still do not improve braking ability the way that larger size brake systems can.

This does not mean that slotted or cross drilled brake sets do not "improve" braking, but they are not the end all to a good system. There are several companies that use cross drilled and slotted rotors in conjunction with larger brake sets. for every last little improvement they provide. But, they do not brake better than a regular large diameter brake upgrade kit. Slotting/drilling is most often used to help dissapate that build up, not to dissapate heat. That is the reason you may find upgrade kits with one or both..but the kits that improve braking are always going to be larger rotors and calipers. If they aren't larger, than they arent going to be much of an improvement other than looks."
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Old 05-03-2002, 12:38 PM   #23
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Exclamation Brake Fluid and Cold Temps

Kinematic viscosities: All brake fluids (DOT 3, DOT 4 and DOT 5) must meet a minimum viscosity test of not less than 1.5 centestokes at 100 C (212 F) and must not be more than the following to meet their various classifications (the larger numbers indicate higher kinematic viscosities just like with motor oils).

DOT 3 1500 Centestokes at minus 40 C
DOT 4 1800 Centestokes at minus 40 C
DOT 5 900 Centestokes at minus 40 C

*-40 C = -40 F*


Higher kinematic viscosities means it "flows easier" at the cold temps.

A centestoke is is 1 mm^2/s


English: The higher the number the more likely it is to turn to goo at low temps. It is a linear relation. So at those cold temps it takes 16% more pressure to flow the same amount of DOT4 as DOT3. This MAY cause an issue with ABS.

By the way, KV does not change in a linear way as temps fall. Up to about 0 F DOT3 and DOT4 are close, but below that DOT4 starts to become more viscous.

Last edited by romanom; 05-03-2002 at 02:05 PM.
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Old 05-03-2002, 01:38 PM   #24
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Default Cold?

40C = 104F, not 40F -40C = -104F Now that is cold, even for MN!

Christian

Edited because I read the post wrong.
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Old 05-03-2002, 02:10 PM   #25
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Default Re: Cold?

Quote:
Originally posted by Chin
40C = 104F, not 40F -40C = -104F Now that is cold, even for MN!

Christian

Edited because I read the post wrong.
I forgot the negative sign, but -40 C = -40 F.

C=0.56(F-32)

C=0.56(-40-32)=.56*-72=-40
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