quick tip for everyone drving around wondering why their brakes work great at slow speeds but not so good on the high way. or vice versa. its because people are idiots...no they are not its just something no one ever really learns. and im here to tell everyone how. (Pascal's law states that pressure applied to a liquid in a closed container transmits equal force undiminished to all sides.) So if you have a master cylinder with a bore of one inch and a wheel cylinder with a bore of one inch. and you apply 10 lbs of force to the master cylinder you get 10lbs at the wheel cylinder. now you can also multiply that force with differnt piston sizes. say you have 1 sq inch piston and a 100 sq inch piston. and you apply 1 lb pressure on the inch piston you have 100 lbs force on the 100 sq inch piston. the problem with this is piston travle decreases as you change sizes. a piston double in size from the first piston will travle half as much as the smaller piston when applied. so the same 1 sq inch piston with 500 lbs force travleing 1 inch transmits to the 2 sq inch piston at 1000 lbs force only travle half an inch. (original 1 inch bore) formaul: pressure = force/area. PSI=450 lbs/area Area= pie R squared= 3.14x5 squared (1/2 of 1 inch) Area= 3.14x.25= 785 sq inches. Pressure = 450/785= (573 psi.) (replacement 1 1/8 inch bore) pressure = force/area PSI=450lbs/area Area= pie R squared = 3.14x5625 squared (half of 1 1/8) Area=3.14x.316=.992 sq inches. Pressure= 450/992=454 psi. so bigger isnt bettter. this systems brake pedal would "grab" much higher than normal. but you would have to use both feet on the high way in oreder to stop. got any questions? class is over. skootch at Skratch's garage.
But I've seen that show and BRUM is only a really small car. He wouldn't need much in the way of brakes and he'd probably not get anywhere near highway speeds. What's all the fuss?
All the above is great info for the hydraulics, but you left out the mechanical part of the equation. You have to include the brake pedal leverage ratio. Will you please present this additional technical information in your next class of Braking 101?
As was mentioned, pedal travel and ratio all figure into the equation too, as does brake design. Are we talking exclusively about drums, or disc/drum combinations, or disc/disc combinations? Class isnt' over...it's barely begun. Pedal ratio is often adjustable through different holes in the brake pedal. Using a master cylinder with a larger bore means a shorter stroke should be all that's needed, but again- many other factors are at play. Vehicle weight is a consideration, as is the brake system design (drums, discs, etc.). The brake system design also may require residual pressure valves based on the location of the master cylinder reservior height relative to the brake cylinders/calipers. I've seen the addition of these valves (which maintain a small level of line pressure to ease the response from the pedal) make a HUGE difference in the way a car stops, or at least how it responds to driver input. The need for an adjustable proportioning valve in custom setups may aid braking performance immensely. Being able to adjust front/rear brake bias so the fronts lock up just before the rears may be all that's required in some systems that "don't work right". Vacuum is also an issue. Most modern systems run a vacuum booster, but few realize how much vacuum these boosters need to operate effectivey. There are now many options out there, from electrically-operated vacuum pumps (which maintain minimum vacuum required for the booster to work correctly) to reconfigured factory hydraulic boosters (Hydroboost) which eliminate the need for vacuum altogether. These Hydroboost systems work off of power steering pump pressure and have been a godsend for those fighting low-vacuum problems in cars with high lift/long duration and/or aggressive high overlap camshafts. There's LOTS more to effective braking than the bore of the master cylinder Amigo. Yes, it's a critical piece in the puzzle, but there are lots of other pieces to consider if one is going to post here and claim to "school" us on the science of braking dynamics... ...especially if that same someone has a screen name painfully close to my own... Scotch~!
i didnt want to blow everyones mind with the mechanical advantage of the brake pedal. the mechanical advantage with pedal ratio depends on what calss lever you use. 1st 2nd or 3rd class lever. 1.first class lever increases force and changes the direction of the force. 2.second class lever increases force applied in the same direction. 3. not important. the formula to calculate mechanical advatange on a first class lever (master cylinder on the firewall.) is pretty simple. you find the distance between between the fulcrum and the pushrod leading to the master cylinder. lets say 2 inches. then you measure the distance between the fulcrum and the brake pad. lets say 10 inches. then divide. total length divided by the distance between the fulcrum and the push rod. 10/2 = 5 = 5 to 1 pedal ratio. so 10lbs of force aplied at the pedal will result in 50 lbs at the pedal push rod. unfortunatly i forget the formula for second class levers. or cars with master cylinders under the floor it isnt much different same basic principles. skootch at Skratch's garage.
i can go on and on about other factors but my main point was about hydrolics. there is plenty of time for my to explain combonation valves, speed sensors friction coefficients. quick take up master cylinders. duo servo. on and on and on. but no one needs to here me yap and if you want to learn about it take a class i was just trying to show a few people the light. skootch at Skratch's garage.
Great brake info! I popped a brake line this week in my truck thanks to some idiot in a Taurus stopping fast and thanks to that great mechanical advantage that the brake pedal provides. http://www.brumpedalcars.com/brum_pedal_car.htm
I'm glad I enrolled in the Braking 101 class. I'll save this thread for future use. Please keep the info flowing. What about brake fluids, system maintenance, grading of friction materials (drum & disc) . What do the letters and numbers on the edge of friction material on drum brake shoes mean? They're there for a reason, aren't they?
you say you are "skootch at Skratch's garage." do you mean THE Skratch? you ever get over to Big Dog's at Foxworthy & Cherry? look for a 300 lb.gorilla in a "51 Hudson with no paint.that's me-george
the letters on the brake bads represent hot and cold friction coefficients. the numbers are there for manufactors purpose. ff it has a COLD friction coe' of 0.35 to 0.45. and has a HOT coe' 0.35 to 0.45. C is the lowest H is the best Z is unrated.just make sure you get a pair that have the same hot and cold coeffiecents. yeah i work for skratch but im from San Jose i go to big dogs on thursdays. but i thught it burnt down. or was that happy days. either way its thursday right now so maybe ill see ya there. skootch at Skratch's garage.
as far as brake fuilds just put dot 3 and be happy. dot 5 is silicone based while 3 and 4 are polyglycol. which means they absorb water easily. poly glycol will absorb 2% of its own weight in water. so you have to make sure you flush your system every year or so. dot 4 does have a higher boiling point so you might want to use it on a hot rod driving down to vegas or paso. but dot 4 will sometimes void the warranty on abs systems. brake fluid is nasty stuff it screws up paint and its poisonsous. on disc drakes after you turn them you always needs to put a undirectional finish on them with sand paper. if you ever here a mechanic tell you that your brakes need to worn in just drive for 200 miles. what he is really saying is that he was too lazy to do the job right. drums just turn em and make sure they are true. skootch at Skratch's garage.
So many words. Don't you have any pictures of rusty car parts or anything? No, actually it's good to see something resembling science here once in a while. But I still like art better than science.
Do you mean: sand from the center of the rotor out to the edge of the rotor? Or do you mean to remove the spiral finish that turning them leaves, by sanding them to leave a circular finish?
you have to take out the groves made by the cutters by taking a flat block of wood and either 400 or 600 grit sand paper. the good stuff. lay it on the block and rub in a circular motion for one minute on each side while it is turning. with moderate pressure.
I like all the good tech info . THANKS It seems like most of the relined or even new brake shoes have a cof of recycled particle board . I'll have to look at the printed letters on what I buy in the future and look for something close to H. Can you recommend a manufacturers brand that comes close to the H? It seems like the brake lining from 20 years ago had better stopping abilities than the new ones on the market. Guess it's 'cause they took the "good stuff" out of the friction material. Do you, or anyone else, know of a source for the old "Velve-a-Touch" metallic or semi-metallic brake shoes? I used this stuff 25 years ago, and it stopped ya'!!!! I'd also be interested for the name of an independent brake reliner that can reline shoes with a GOOD friction material. I'm not interested in a long lasting lining (ie. 40K mile warranty like is always advertised at the chain auto parts stores). When everything in the brake system is perfect and ya' feel like you're on an airplane glide path when ya' put on the brakes, I think the friction material is suspect.
the best i think is raybestos. but usually you want to stick with the factory brakes. so buy it from the dealer.
Scootch, Scotch, Scratch, Screech?? Damn I'm confused. To be a hydraulic engineer your spelling is screwed. BUT The info is very good.
I'm right here. Keeping an eye open. For better performance pads, check into the new units Baer is selling. I also have had good luck with Hawk brand pads. Of course, I don't run too many factory brake systems anymore, but I know the Scandanavian pads Baer is selling are factory replacement for lots of stock applications. They showed me the research data from the lab and it was quite impressive. The pads last longer and bite better...that's cool stuff. They are more expensive, but if they last longer, its worth it. The improved braking performance is worth a few more of my coins. I'll tell ya what Skootch...Its not that I don't believe you know what you're talking about. I honestly believe you do. I just have great trouble understanding your posts due to stuff like grammar and spelling. I'm picky about stuff like that, but in a tech post where folks are honestly trying to learn something, it's extra important..especially if that tech post relates to the most critical safety system in any automobile...the brakes! Just my two cents... Scotch~!
well i do aprecciate your replies. but keep in mind, i am only 19... "and then everyone freaked out." yep fresh out of high school. 04. i am certified ASE for brakes... scary thought i know. and paint and body. and shooting for A/C and suspension. So forgive my grammer and spelling i know that you were an editor so its more than understandlable. but just trying to share the know how. skootch at Skratch's garage.
That makes it an even more egregious error on your part...if'n you're fresh outta school, you ain't go no excuse for poor grammar & spelling. Another lesson they won't teach you at ASE is that theory is...well...just that, theory.
Finding good quality disc brake pads for a variety of intended applications isn't a problem. But, finding good quality drum brake linings is!!!! And, I'm not concerned about wear, I just want something that will stop.
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