Archive for the ‘Brakes’ Category

Breaking in Your Brakes

April 18, 2010

Without getting too much into the theory and mechanics of how brakes work or how to repair and replace your own brakes, I would like to explain how to ensure that your brakes are working the best that they can regardless of who installed them.  When my sister got a slightly used VW Bug a few years back with 30,000 miles on it or so, the first thing I did was take it for a drive and see how well everything was working.  One of the many items I checked were the brakes, which were OK, but just seemed like more pedal pressure was needed to stop the car than it should take and they were just all around not that impressive.  A VW Bug is a small light car with good sized disk brakes all around and it should be very capable of stopping, not just OK.  The brakes on that car are very impressive when they work right.  The operative phrase being: “when they work right”. 
 
What’s wrong with the brakes? 
 
The truth is that nothing was wrong with the brakes.  They just hadn’t been seated or “broken in”. 
 
When stopping your car, the brakes must convert all of its momentum into some other form of energy; in this case that form of energy is heat.  Conversion of motion energy into heat energy is done by the friction between your brake pads brake rotors.  In order for this conversion to happen it is important to have as much contact patch area as possible between the pad and the rotor.  When new brake pads are installed onto a car, the pads will not mate perfectly to the rotors until they have a chance to wear into each other.  Because of how brake rotors are machined and the nature of manufactured parts this surface that looks even to the naked eye is in fact not even at all.  All machined surfaces like pads and rotors have lots of little grooves in them.  After your break pads have been seated there will be more surface area contact between the pads and rotors which improves the performance of your brakes.
 
Why would I intentionally wear brakes? Isn’t brake wear bad?
 
Extreme wear is bad, when the pads wear out completely, but that is not the kind of wear we’re talking about.  All new mechanical machines will usually have a break in period, like the break in period on a brand new car.  During this period all of the part surfaces are wearing off machine marks and neighboring parts are matching eachother’s profile so that they will work together better after they have “grown accustomed” to eachother.
 
How did I figure out that the brakes weren’t up to snuff?
 
Easy, when driving the car down the road find a back street or somewhere with very little traffic and preferably not a residential area.  Make sure there is nobody within 300 yards behind you and slam on the brakes as hard as possible from about 30mph.  If your car has ABS you should feel and hear the horrible noise that the ABS pump makes when it is running.  Don’t worry, you’re not breaking it, that’s what it’s supposed to do.  If the car doesn’t have ABS then you should hit the brakes hard enough to lock up the tires and then use threshold braking to bring the car to a stop.  This maneuver should throw you and any passengers fully into your seatbelt.  As the car comes to a stop the pressure pushing you and any passengers into the seatbelt should get stronger and stronger.  (Tip: you might want to make sure and warn your passengers what you’re doing and make sure that nobody has a coffee or a coke which will make a mess and that you don’t have 50 shopping bags in the trunk which are going to crush the bananas you just bought from the grocery store.  If your type of humor loves these things called “brake checks” then that’s fine with me).  When you slam on the brake pedal as hard as you can the stopping power should immediately throw you into the seatbelt hard enough to lock the seatbelt and you shouldn’t have to use all of your leg muscles to activate the ABS or to lock up the brakes.  If you do have to use lots of power or the brakes take a bit to apply force, then most likely the brakes have not been seated properly. 
 
The pads weren’t broken in after 30k miles?
 
In truth, I don’t know if the pads had been recently replaced on the car or not, but I don’t imagine they would have been with a car that has this few miles on it.  If the previous owner had a habit of stopping early and lightly and never needed to use the brakes very hard at all, then they never would have seated the whole pad to the rotors.  All metals and parts flex when pressure is applied to them.  When breaks wear in at light load conditions then the wear patterns will match the conditions they are used in the most where there is very little flex pressure on the brake calipers.  So in that case the breaks will have the best contact patch when light load is applied to them, but not in the situation that you actually need them to work the best which is under hard stopping conditions.
 
Why don’t shops or manufacturers do this procedure?
 
Mainly because of the cost and liability.  Can you imagine a brake shop having to send someone to find an empty back road for each car they work on?  Brake shops charge enough as is!  Plus the liability and insurance needs of having teenagers or college students pushing the cars brakes to the limits?  Brakes will work reasonably well without this break in procedure and will eventually wear themselves in during normal stopping if the driver isn’t overly conservative.  Some performance shops may do this procedure but I haven’t ever heard of one.
 
How to do it: Break in your Brakes Baby!
 
Ok, so now that I’ve convinced you that you want to make your breaks work better I’ll have to convince you to do this crazy seating procedure.  Go find a flat straight empty back road which you can see for miles to ensure that no cars are anywhere near you when you do this.  It’s probably a good idea to do it where there aren’t big ditches to accidentally drive into and make sure there’s not any majorly broken or uneven surfaces that will make your car drive unpredictably under heavy breaking.  We’re going to do eight hard stops to seat the brakes so you need lots of room.
 
Drive to ~30 mph and slam on the brakes as hard as possible to activate the ABS if you have it or to threshold braking if you don’t have ABS.  Brake hard to about 3 mph but don’t bother coming to a complete stop.  Keep in mind that you want to put the brakes to their limit just like you would if you were in a real emergency situation.  You should be thrown into the seat belt, your sunglasses be on the floor and your coffee cups be empty by the time you’re done (whether the coffee is spilled on the dashboard or you were smart enough to empty them before starting).  Do this three times.
 
Drive to somewhere between 50 and 60 mph and do the same extreme braking exercise five times from ~55 mph to ~3 mph.  While you are doing this you should be able to feel a drastic improvement in stopping power.  When I set in the brakes on my 350Z sports car the brakes were smoking (not the tires) by the time I did the fourth and fifth stop.  This isn’t necessary but it lets you know what kind of stopping we’re doing here.  You should definitely smell the brakes by the time you’re done whether they smoke or not.  If you drive a large vehicle such as a full size truck, SUV or van it may be a good idea to let the brakes cool off for a minute or two between brakes so you don’t overheat and warp them.
 
Congratulations!  Your car is now safer and this world is a better place because of you.   
After you’re all done you should be proud of yourself!  And now you know how fast your car can really stop, it’s probably a lot better than you thought, and it should be even better now than when you started.  My brother and I did this on my Dad’s mini cooper after replacing the pads and rotors.  Boy did it make a difference!  It went from a heavy pedaled slow stopping machine to a serious “stop on a dime and still have nine cents left” animal!
 
Disclaimer:  I am not aware of the condition of your car or your driving ability.  I recommend this procedure be done on a safe and functional vehicle with a safe and competent driver.  I am not responsible for the stupidity or ignorance of people following these procedures should they become apparent during these procedures.  All road laws should be observed while following this procedure and special attention paid to safety.  The point is to improve the safety of your car so don’t hurt yourself or someone else trying to do it.

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