Properly Bleed Mustang Brakes
Using the proper tools and procedures is the key to a firm brake pedal
From the October, 2012 issue of Mustang Monthly
By Mark Houlahan
Photography by Courtesy Phoenix Systems
You've read the title of this story on the contents page and probably flipped to this story wondering "what can really be new in brake bleeding?" Well, if you're still asking your wife to sit in the car and pump the pedal (and don't forget yelling "holding" or honking the horn--if it works) then yes, there's plenty to discuss in regards to properly bleeding your Mustang's braking system; be it classic or late-model. From using the proper tools to different bleeding procedures, there are several ways to get the job done right and, usually, without the help of a second set of hands (or feet as it may be).
So why do we need to bleed our braking systems anyway? For the majority of us, it's typically because of a brake component upgrade or service replacement. Upgrading to discs on the front of your '66 Mustang; or adding those Ford Racing Brembos to your S197 means having to bleed the system for the new components to function properly. Servicing leaking components or replacing worn parts--such as brake hoses, master cylinders, and more--all mean you'll have to go through the brake bleeding process as well. Finally, you may not realize it, but brake fluid is hygroscopic, meaning it attracts water. Copper corrosion from brake lines is also another real issue. This contamination is what causes rust in your brake system and wreaks havoc on seals and other rubber parts. As such, it's recommended to completely flush and refill your entire brake system with fresh fluid every two years. When was the last time you did that?
Bleeding your brakes takes a few special tools and a bit of patience (and common sense), but it's not difficult, even for newer cars with tricky ABS and stability control systems. Best of all, with the procedures we'll show you here to properly bleed your brake system for a firm pedal and great stopping, brake bleeding is so easy you may actually look forward to that two-year flush and fill regimen for all your cars!
1 Bleeder screws are where...
1 Bleeder screws are where the majority of your bleeding process will happen. As such, you need a quality tool to break them free and quickly open and close them as needed. A tubing or "line" wrench, like the Snap-on shown here, or a specialty bleeder wrench like the K-D Tools shown at the bottom, are both great choices.
2 The tubing wrench is designed...
2 The tubing wrench is designed to grab all of the corners on the bleeder screw, giving it more support and preventing rounding of the bleeder screw's hex. Cheap wrenches will flex and still round the fitting, so be careful.
3 Sometimes the overall thickness...
3 Sometimes the overall thickness of a tubing wrench thwarts your best efforts at getting to the bleeder screw, which is why we still keep this K-D Tools bleeder wrench in our collection of tools. The wrench has a smaller profile, and fits drum brake bleeders especially well. In a pinch we've even used sockets and a quarter-inch ratchet, but wrenches are your best bet.
If you check your workshop shelf, you probably have a bottle of brake fluid from the parts store sitting there that's a good year or two old from your last brake project. Is that brake fluid any good? It all depends upon how well sealed the bottle is, but we prefer to not take chances and use new, unopened bottles with every project. While we're looking at brake fluid, have you looked at the fluid in your master cylinder lately? Just because it isn't clear doesn't mean it's bad. Brake fluid can turn dark from brake hose rubber dye and assembly lubes, and while moisture is a concern, the real issue with brake fluid failure is copper corrosion. This copper residue is what ruins seals and ABS hardware. You can easily test your brake fluid with BrakeStrip test strips. It's a simple package of test strips and a rating chart. Dip the test strip in your master cylinder and after 60 seconds compare it to the chart. On the '11 Mustang GT we tested, the brake fluid spec'd out fine, but what about yours? Lastly, and this is another simple product that's great for someone who's working on their brake system for the first time, there's BrakeStrip ID. The BrakeStrip ID product is a similar test that will help you determine what type of brake fluid is in your system. This way you can top off, or refill with the same DOT fluid type.
Brake Bleeding Tips
- While reverse bleeding is often most effective, some cars benefit from a mixture of pressure, gravity, and reverse bleeding
- Bleed your brake circuit from right rear to left rear, then right front to left front. Always start at the farthest point from the master cylinder, especially on vintage Mustangs that do not have split brake circuits
- Follow manufacturer's instructions when bleeding the proportioning valve to prevent tripping the brake circuit warning light
- When servicing calipers, always remember to return them to the proper side/position so that the bleeder screw faces up
- Use a light coating of wheel bearing/heavy grease, or a single wrap of thread tape on bleeder screw threads to prevent air from seeping around the threads and causing a difficult bleeding job
- Brake fluid is harmful to paint, ensure that all work areas are covered, including below the master cylinder (framerail, inner apron, etc.)
- Tap the caliper or wheel cylinder with a rubber mallet a few times to dislodge air bubbles clinging to the walls of the fluid chamber before bleeding
- Use a high temp performance fluid if you plan on hard braking--like track use--and flush the fluid regularly
- Check your master cylinder reservoir(s) frequently for low or high fluid situations, depending upon bleeding process, and refill or suction the excess
- DOT5 silicone fluid is not recommended for street use, and you should use DOT3 or DOT4 fluid depending upon your brake system
4a If a bleeder screw is...
4a If a bleeder screw is rusted and giving you fits, don't try to be a hero and reach for the Vice-Grips. Instead, look into this nifty tool called Brakefree from Phoenix Systems.
4b The tool locks into your...
4b The tool locks into your pneumatic hammer and has a 3/8-inch socket end to fit the proper sized socket for the frozen bleeder. While vibrating the bleeder with the hammer, you then turn the tool back and forth with a 3/4-inch wrench to free the stuck bleeder. This tool works on all sorts of frozen bolts too as a bonus!
5 Before getting into the...
5 Before getting into the actual brake bleeding process, it is always a good idea to give the braking system a complete inspection. Any leaks or hardware out of adjustment can cause a soft pedal; tricking you into thinking you have air in your system. Brake hoses and banjo fittings (on late-model brakes) use copper sealing washers on the bolt or hose end. Be sure a sealing washer is in place and the line is secure. We recommend replacing these washers any time the connection is opened.
6 If you've ever replaced...
6 If you've ever replaced a master cylinder on your Mustang, then you're intimately familiar with the "fill and plunge" bench bleeding method--hooking up the little transfer hoses and pushing the dickens out of the master cylinder piston with a screwdriver. It works, but it's messy and requires the use of a clamp or vise to hold the master cylinder.
7 A better way to fill your...
7 A better way to fill your master cylinder, which can be done right on the car, is to use something like Phoenix Systems' brake bleeder. Theis brake bleeding tool can be used for traditional vacuum bleeding, pressure bleeding, and reverse bleeding where the fluid is injected into the part. Phoenix Systems calls this Reverse Fluid Injection, or RFI.
8 Basic brake bleeding often...
8 Basic brake bleeding often starts with what is called gravity bleeding, where all bleeder screws are opened and the system left to self bleed--closing the bleeders off one by one as they start to drip. This is usually followed by the old foot pumping method; however a quality hand vacuum pump will make it a one-man job.
9 The one problem with the...
9 The one problem with the foot pumping and vacuum pump methods are that you are inevitably going against science. Air in liquids rise--just look at the bubbles in a glass of soda. With the Phoenix reverse bleeder's RFI technique you inject new fluid at the bleeder port, forcing the air up and venting out the master cylinder, making for a more effective bleeding operation that takes less time and provides a firmer pedal.
10 Phoenix Systems' MaxPro...
10 Phoenix Systems' MaxPro bleeder is used here in our shop. Simply fill the supply bottle with fresh fluid (or use the bottle adapter to fill right from a brake fluid bottle), connect the proper fitting to your bleeder screw, then open the bleeder and inject the new fluid into the system.
11 While the MaxPro is an...
11 While the MaxPro is an all metal pro-shop level tool, if you're only working on one or two cars a month, the V12 and V12-DIY reverse brake bleeders are made from Zytel nylon to be lightweight, yet strong. All reverse brake bleeders come with a selection of bleeder fittings and adapters and an instructional DVD hosted by Stacey David of Gearz TV.
12 While getting all the air out of your brakes' hydraulic system is key to a firm pedal and proper brake operation, if you have issues elsewhere no amount of bleeding is going to fix it. You can check your brake system from end to end with a diagnostic kit like this one from Master Power Brakes. The kit includes a master cylinder to brake-booster depth gauge, a vacuum gauge for reading vacuum, a pressure gauge with adapters to check fluid pressure at the master cylinder and wheel cylinders/calipers, and a fluid injector for bench bleeding. We've used every part in this kit and, for the investment, it saves time and takes the guesswork out of just throwing brake parts on and hoping it fixes the problem.