From the February, 2011 issue of Circle Track
By Jeff Huneycutt
This is Phoenix System's MaxPro.
It doesn't take a new race team long to learn that brakes are right up there, in terms of overall importance to performance, with the engine. A quality braking system isn't just for avoiding crashes or making sure you don't run off the end of the trailer, it's also important for controlling turn entry, loading the front wheels to help the car turn, and on dirt tracks helping control the car's pitch as it slides through the turns. In short, better and more consistent stopping power usually translates into faster lap times and improved performance on the racetrack.
Of course, like everything else in racing, there's more to it than simply buying the best parts and bolting them on. Along with the tires and valvetrain, the braking system probably requires as much time and attention as any other single component on the race car.
And the main reason for that is primarily the brake fluid. Everything else, from the pedals to the pads, can be pretty hardy and resistant to abuse. Other than knocking the glaze off of a set of pads or checking to make sure the rotors haven't warped from heat, the rest of most braking systems are quite dependable. The problem with brake fluids is they are hydroscopic, which is simply a fancy word for "absorbs water like a sponge."
For racers on a budget. Phoenix System's V12 DIY
Avoid the H2O
Hydroscopic materials (some may also call them "hygroscopic") include salt, sugar, and obviously, brake fluid. These materials will attract water so strongly they will actually pull it out of the moisture in the air around them. That's why salt will often "cake" if not kept in a sealed container. With brake fluid, the results of exposure to moisture aren't as easily seen. In fact, in street cars it may not even be noticeable.
Like brake fluid, and 99 percent of all other liquids, water is non-compressible, so it actually works quite well as a hydraulic mechanism to transfer the force from the driver pressing the brake pedal to the pistons in the calipers pressing the brake pads against the rotors. The problem with water is it has a depressingly low boiling point (212 degrees F). When moisture is present in brake fluid it drastically lowers its boiling point, and we all know that one of the main byproducts of the friction between the brake pads and rotors used to slow the car down is heat. When the moisture reaches its boiling point, it turns to steam right there in the brake lines or caliper. That steam, in turn, produces air in the system which is easily compressed and you wind up with the dreaded "spongy pedal."
We tested the Phoenix Injector.
There is also another byproduct of boiling brake fluid. When that moisture turns to steam, it not only creates compressible air in the system, since steam also takes up more volume than the water it came from it also creates pressure. Think about the steam engines on trains in the old cowboy movies. This excess pressure can grow enough to actually push out the pistons on the brake calipers, causing the brakes to drag.
It all adds up to a recipe with all the wrong ingredients when it comes to racing. Race car braking systems produce extreme heat, making it more likely to boil the brake fluid and produce a spongy pedal. And that loss of performance and pedal feel will force the driver to apply the brakes earlier and stay on them longer in order to get the same result, giving the brakes less time to cool off before the entry to the next turn. You can see where it goes from there. The driver not only gets poor pedal feel and pitiful braking performance, but the brakes are also dragging all the way around the track, killing horsepower at the wheels.
New Tool for an Old Job
That's why race teams must flush the brake system as part of their regular maintenance schedule. Of course, not only must the brake lines and calipers be flushed of the old brake fluid, you also have to be careful not to allow air bubbles to be introduced into the system at the same time, which is easier said than done. After all, the entire goal is to keep air out of the system to ensure a nice, firm pedal and lots of brake response.The old-school method, which works fine and many racers swear by, is to crack open the bleeder on the caliper, pop the top off the master cylinder and activate the brakes to push the old fluid out of the lines. The problem with this is it requires two people: one to work the brakes and a second to open and close the bleeders and also keep the fluid in the master cylinder topped off. You can only do one caliper at a time, so it's also a bit time consuming. As CT's Project G.R.E.E.N. team recently found out.
The first step is to prime the Injector. This is done by hooking both the intake and outlet hoses to the collector bottle. Now you can pump the injector and recycle the fluid until all the air is out of the system.
Phoenix Systems includes a wide variety of adaptors designed to help you work with practically any brake system you can imagine. Not everything is needed for every job. Once you figure out just the components you need to work the brakes on your race car, things will get a lot simpler.
Here's the rubber boot that we chose to work with our calipers. Notice the twist-lock fitting on the end.
Phoenix calls the twist lock fittings it uses "Luer fittings." They provide a nice, positive seal with approximately half a turn. Plugs, which you can see here, are also included to keep brake fluid from leaking onto your shop floor. They also help you keep air bubbles from contaminating the system while you are hooking everything up.
A second method is to open all four bleeders at once as well as the cap on the master cylinder and allow gravity to bleed out the lines. You can do this method by yourself, but it takes even longer and the fluid is exposed to the air even more.
But there are tools on the market that make the job a bit easier. One of the most complete designs that we've ever seen is the Phoenix Injector from Phoenix Systems. It is unique in that it is designed to be used several different ways to fit your needs, increase the quality of your brake system maintenance and, to be honest, make an aggravating job a little easier.
The Phoenix Injector isn't a single product; instead, Phoenix Systems has built several packages around the Injector design to fit different pricing levels. Phoenix has been around for years, and its products are popular in car repair shops. But now Phoenix is marketing brake bleeding kits for racers and other high-performance applications. We tested the MaxPro Professional kit to see how useful it would be for race teams.
There is also a system for pulling brake fluid directly from new containers. The cone works with containers with different size openings and also help keeps air away from the fluid. It forms a seal around the opening of the container, and there's also a tight seal around the tube you insert into the container to pull the fluid out through.
The greatest feature of the Phoenix Injector is that it pressurizes the fluid to either inject it into the brake system or creates a vacuum to pull it out. It does both equally well, so which method you choose depends on your preferences and specific situation. But the result is brake system maintenance that can be done by yourself, faster, with less mess, and less exposure to air than ever before.
Pressure Bleed and Flush
Most racers bleed the brakes after every race. Completely flushing the system isn't necessary as often, but it should be done at least a few times over the course of the season to keep the fluid fresh. If you use a stock master cylinder, you can use the Phoenix Injector to push pressurized fluid through the system from the master cylinder down through all the calipers. This is much faster and more efficient than pumping the pedal or the gravity feed methods. Unfortunately, this will only work with stock master cylinders (as far as we can tell). When we tried this method on a race car outfitted with Wilwood master cylinders, a fitting at the bottom of the reservoir kept the injector from sealing.
If, however, you can use the pressure flush system on your race car, set up the injector so that it pushes fluid down through the master cylinder. Then, crack open one bleeder valve at a time, attach the capture container at the bleeder valve to keep the oil fluid off of your shop floor and inject fresh fluid into the system until you see the dirty fluid coming out of the caliper turn the color of the new, fresh fluid. Phoenix Systems also includes a one-way check valve you can install between the caliper and the catch bottle to keep oil fluid from accidentally getting siphoned back into the caliper.
The containment bottle can be used either to pull fresh fluid from or to catch oil fluid exiting the calipers. It includes a very strong magnet that you can attach to the chassis or a bar to locate it practically anywhere you like on the race car. There is one fitting on the cap for pulling fluid out and another for dumping fluid into the bottle.
Vacuum Bleed and Flush
With this method, instead of pushing pressurized fluid into the system from the master cylinder, you use the Injector to create a vacuum in the caliper and pull the old brake fluid out of the calipers. With this method, simply reverse the Injector so that the back of the "gun" is attached to the caliper, crack the bleeder and pump the Injector so that the old fluid is emptied into the capture bottle.
You will also need to keep an eye on your master cylinder and refill it occasionally as the fluid level drops to keep air from entering the brake lines.
RFI
The third, and possibly most interesting, method is called "Reverse Flow Injection" or RFI for short. This method is just for bleeding the brakes to make sure there are no air bubbles trapped in the lines. It is not suitable for flushing all of the brake fluid.
RFI takes advantage of the simple fact that air bubbles want to rise in a fluid, not sink. So, instead of trying to force any air bubbles out of the bleed screws on the calipers-which is one of the lowest points on the entire system-this method sends the air the way it wants to go anyway, up and out the master cylinder reservoir.
Here, Sims is bleeding the brakes with the RFI method. He's injecting clean fluid into the caliper to push any air bubbles up and out the master cylinder reservoir. Also notice the flashlight mounted on top of the Injector. This is to help you see what you are working on in the event you have to bleed or flush the brakes in the pits at the racetrack. Most racers don't have to do this often, but if you are faced with the task, a light certainly will be helpful, as the Project G.R.E..E.N. guys found out.
To do this, attach the injector to the caliper bleed screw so that it is injecting fresh brake fluid into the caliper. Begin, as you always should, with the caliper farthest from the master cylinder and work your way so that you finish at the caliper closest to the master cylinder (normally the left front). Also, lightly squeeze the Injector handle before attaching the end of the line to the bleeder screw to make sure there is no air in the Injector or attached hose. Phoenix Systems says that only three to 10 full pumps are needed at each caliper to do the job.
Then, after removing the Injector, allow a small amount of fluid to drip from the hose connected to the bleeder valve in order to "burp" any trapped air from the brake system and close the bleeder valve.Overall, the Phoenix Injector system worked very well. There are a lot of components involved, and hooking everything up can seem a bit complex at first. But once you get the hang of it, you will find that it will help you maintain a firm pedal and good braking performance every time you go to the racetrack.
This is an in-line filter to help you keep the Injector clean when pulling old fluid out of the calipers by using the Injector to create a vacuum.
Choose The Right Fluid
You may hear about some special types of brake fluid on the market that aren't hydroscopic and won't degrade by absorbing water. And it's true, this fluid is silicone based and won't draw moisture. At first, that may seem like the perfect answer to all your brake system problems-they also have a DOT 5 rating which means an extremely high boiling point-but resist the urge to put either in your race car.
According to information provided by Afco Racing Products, Silicone-based Polymer brake fluids are sold for street applications and are popular among the show-car set because they don't eat paint like traditional brake fluids. But they have one particular drawback, and it's a big one.
Silicone-based fluids are highly compressible. So even with fresh fluid in a perfectly spec'ed out brake system, you won't be able to get rid of the feeling of a spongy pedal. And it only gets worse as the temperature of the fluid rises. So even if it never hits its boiling point, silicone-based fluid is going to provide poor braking performance and rob you of any feel from the pedal. Don't be fooled by the DOT 5 rating, which many racers equate with performance. Silicone-based brake fluid is not a racing quality product.
Here, Sims uses the vacuum method to pull oil fluid from the caliper and dump it into the canister.
A Good Reason To Flush Your Brake Fluid Regularly
A long with the valuable tip to stay away from Silicone-based brake fluids, AFCO also passed along this chart listing the boiling temps for brake fluids with different DOT (Department Of Transportation) ratings.One important thing to note is that the dry boiling point for many of these fluids can actually be higher than the rating. For example, AFCO says that its 570 Degree brake fluid is rated DOT 3 but has a dry boiling point of 570 degrees F. (Wonder where they got the name?) But even though its boiling point is 169 degrees higher than DOT standards, it still gets a category three rating because of its wet boiling temp. This is true for any poly glycol-based fluid (non-silicone); the dry boiling point is going to be significantly higher than wet. And since race cars produce much more heat in the brakes than street vehicles, boiling the fluid is much more likely. This chart with the DOT ratings illustrates just how important it is to flush your brake fluids regularly.
|
DOT Rating |
Dry Boiling Point |
Wet Boiling Point |
|
DOT 3 |
401 |
284 |
|
DOT 4 |
446 |
311 |
|
DOT 5 |
500 |
356 |
|
DOT 5.1 |
518 |
375 |
| Note: All temperatures listed are degrees Fahrenheit | ||
