How to Bleed Brakes on a Jeep Using DIY Tools
Jeep Brake System Maintenance: 101
Your Jeep's brake system is more important than the engine. The engine will make it go, but the brakes are what make it stop. A poorly functioning engine will just make it go slower, but poorly functioning brakes will make it dangerous. No short cuts are acceptable when you're dealing with your Jeep brake system. Replacing brake pads, shoes, rotors, and drums is what the typical brake job entails. Swapping out the consumable brake components becomes a normal ritual that becomes so familiar it is easy to pull out all the tools needed before the job even begins. However, it's not until those tires come off and you start digging in that you get a good sense of the mess you're dealing with.
There are a number of gremlins that you may come across as you are disassembling the old brakes. An obvious mess of brake fluid would indicate a blown-out caliper or wheel cylinder seals. If brake pads / shoes are worn more on one side of the Jeep than the other, take a close look for non-functioning calipers or wheel cylinders. There may be a caliper or wheel cylinder that has a piston that is ceased and not providing any pressure to the respective pads or shoes. On a disk brake system, if the pads are worn unevenly on the same wheel then it is likely that the floating caliper mounts are gummed up and not allowing the caliper to apply even pressure to both brake pads. Brake hoses are another thing to inspect. If there are any signs of cracking, dry rot, pinching, or fluid weeping, then it is time to replace your hoses.
What do most of these situations have in common? First off, your quick brake job just got more complicated and is no longer going to be "quick." Second, the seal must be broken on the brake hydraulic system to replace a master cylinder, caliper, hose, line, or wheel cylinder. Once a connection is broken on the brake system, air contaminates the system. After the new hydraulic parts are installed it is time to bleed the system to rid it of all air. If any air remains in the brake system, the Jeep will have a spongy brake pedal that may take a couple of pumps to build decent braking pressure. A firm pedal on the initial stroke is what we are after. There is no time to pump the brakes multiple times in a panic stop situation. Here are some basic techniques to getting the job done right, and a look at a couple of different tools available to make the job easier.
Replacing and Bleeding a Master Cylinder
The master cylinder is the heart of the braking system on any vehicle. They typically do not fail often, but when they do it can really ruin your day. Keep an eye out for any leaks around the firewall that would indicate a leaking seal. A soft or squishy pedal is another sign it is not working properly, provided you have confirmed that there is no air in the system. When replacing a master cylinder, you must first bench bleed the unit. A simple master cylinder bleeding kit can be found at your local parts house. It comes with a selection of threaded adapters to fit the output ports and some pieces of tubing. Fill the reservoir with brake fluid and route the tubes back into the reservoir. With the master cylinder held sturdy in a vice, pump the piston over and over again until there are no more air bubbles passing through the tubes as you pump it. Remove the bleeding tubes, plug the ports, and secure the lid before mounting your newly bled master cylinder into your Jeep.
Once the pre-bled master cylinder is mounted in the Jeep, the simplest way to bleed the rest of the system is to find a buddy to help. If no buddies are available then kindly ask your significant other to turn Southern Charm off of the TV and schlep on out to the shop to, "help for 5 minutes!" That's true love my friends. Putting a clear piece of 5/16" diameter tubing over the bleeder valve helps keep the mess contained and allows you to see if there is any air coming out of the valve. The person working the bleeder screw will instruct the hired help to pump the brake pedal 4-5 times and then to hold pressure on the pedal. The bleeder will then be cracked open turn with a wrench to release the pressure and bleed out the air and old fluid. The bleeder screw is then closed, and the hired help pumps up the system again to repeat the procedure until the fluid runs clean and with no air bubbles. Typically, the passenger rear is bled first, then the driver rear, followed by the front passenger, and finishing up with the driver front. The cycle may need to be repeated if the brake pedal still feels soft, indicating that there is still air present.
Bleeding the Brakes
There are some tools available out there to facilitate the one-man-band brake bleeding party. This is the Phoenix V12 brake bleeding kit. The kit comes with the adapters needed to bleed most braking systems. Additional master cylinder screw-on cap adapters are available as well that are sold separately. The instructions are clear and easy to follow, but if you're more of a visual learner then maybe the instructional DVD featuring automotive legend Stacey David is more your style. Versatility is the key to this setup, lets take a closer look at all the capabilities it has.
The Phoenix V12 bleeder can be fitted with a rubber nose cone adapter that screws onto the front nozzle. A suction line on the back of the gun draws brake fluid directly from the bottle into the pressure piston using a cool no-spill cone adapter in the bottle. Squeeze the gun handle while firmly pushing the nozzle into the brake line port to form a seal. This fills the piston from the bottom up and pushes all of the air into the reservoir. The instructions call for the lid to be off so that you can see when all of the air bubbles are out. It doesn't take much fluid pressure to shoot a volcano of brake fluid out of the reservoir and across the work bench, as you can tell from the fluid stain. After that charade, I chose to leave the lid on for most of the master cylinder bleeding process to avoid a mess.
After the master cylinder is bench bled and mounted to the Jeep, the Phoenix V12 bleeder can be used in several different configurations to then bleed the remainder of the brake system. For an open top master cylinder, the rubber cone nozzle is used again. This time though we will be working with the intake ports inside of the fluid reservoir. Start by opening the rear passenger bleeder valve on the caliper or wheel cylinder. Then squeeze the gun slowly to force flush new fluid though the lines. This is an easy way to both bleed out any air that is in the system and also replace old cruddy brake fluid with new.
On the wheel side of things, the adapter hose that fits onto the bleeder valve is fed into an empty container to catch all of the old brake fluid. If your fluid is as spent as ours was, then it will be easy to distinguish the darker old fluid from the new clear fluid. The junk fluid bottle made its way around to each corner of the Jeep as we went through the bleeding cycle.
If your master cylinder is too difficult to reach for pressure bleeding from the top-down at the master cylinder, you have the option of vacuum bleeding at the caliper / wheel cylinder. Attach the bleeder valve adapter hose twist-lock quick coupler to the back side of the Phoenix V12 gun. A plain hose is attached to the front of the gun to dump the fluid into an empty container. As you pump the mechanism it will draw the fluid down through the system with a suction. When vacuum bleeding you will usually draw some air past the threads on the open bleeder valve and into the suction source. The air is not getting back into the braking system, but it can trick you into thinking there is endless amounts of air in the system.
There is also the option to flip your adapter hoses front to back and pressure bleed from the bottom up to the top. Forcing fluid from the caliper / wheel cylinder up to the master cylinder. You will need to keep an eye on the fluid level in the reservoir and remove fluid from the master cylinder as needed. A mechanics fluid syringe or a small scoop can make quick work of that. You especially want to make sure to remove the old discolored fluid the best you can when reverse pressure bleeding like this.
Final thoughts on the Phoenix V12 bleeder: The instructions were great. The twist lock adapters made a good seal and did not leak. The versatility of being able to bleed a master cylinder, pressure bleed the system from the top-down, pressure bleed from the bottom-up, or vacuum bleed is fantastic to be able to adapt to any situation. However, the return mechanism on the trigger seemed to stick often and needed to be pulled back manually. Not ideal. At the end of the day though this unit worked well with a little operator training.
Vacuum Bleeding the Brakes
Vacuum bleeding always seemed to be the ticket to bleeding brakes by yourself. When the time came, the OTC 8100 manual / pneumatic was the unit of choice. It comes outfitted with a 10-quart fluid tank to catch discarded fluid. Suction is created by either hooking it up to an air compressor source, or by pumping the T-handle manually. There is an adapter for bleeder valves as well as 4 different hose attachments for all kinds of fluid evacuation situations. One of the down sides is that this tool does not help bleeding a master cylinder. We don't see that as a big deal though.
The sequence of bleeding is always the same, the wheel that is furthest from the master cylinder. With the OTC 8100, attach the brake bleeder hose quick coupler to the vacuum unit, and the place the rubber adapter onto the bleeder screw. Hook up the air compressor hose and then open the valve to allow the air to flow into the unit. Next, open the valve to the suction hose to begin pulling a vacuum on the system. Open the bleeder screw and brake fluid will begin to flow into the tank. Notice the dark nature of the old fluid in the suction tube.
The front brakes are next. In this view it is easy to see how the hoses hook up to the bleeder screw, simple enough. While the pneumatic operation of the OTC 8100 is fairly self-sufficient, you need to keep an eye on what is happening in regard to the fluid movement and if air is being removed.
No matter what technique you are using to bleed the brakes, this is a perfect example of what you are looking for. Notice the air bubbles that are visible in the clear bleeding hose. That is air that was flushed out of the braking system. When solid fluid flows through the tub with no air bubbles, the bleeding is complete for that corner. Move on to the next!
With any of these brake bleeding techniques one of the most important aspects is making sure that you never let the master cylinder run dry during the bleeding process. If you come to find that the master cylinder has indeed gone dry, you have pulled air into the system from the top and will need to start the bleeding process over from the beginning.
The OTC 8100 fluid evacuator has more tricks up its sleeve though. Using some of the other suction hose adapters you can easily drain the fluid in just about any gear box, pump, reservoir, transmission, transfer case, or engine. It sure was nice to be able to change the gear oil in the rear axle of our Jeep without having to remove the differential cover, scrape the old gasket off, clean everything well enough for the new seal, and then make a mess with gasket sealant.
Our final thoughts on the OTC 8100 fluid evacuator:
The concept is pretty straight forward. Even though the operation is basic, the operating instructions could have had more detail on using the vacuum to bleed brakes specifically. The vacuum made bleeding the brakes easy, but this method tends to pull air into the suction line past the threads on the bleeder valve. That air isn't getting back into the brake lines, but it makes it difficult to evaluate your bleeding status. It did get the job done though. As an added bonus outside of bleeding brakes you now have the ability to cleanly remove fluids from all kinds of different places.