Replacing Brake Lines on a 1999 Ram 1500
The 1999 Dodge Ram 1500 came with a standard dual-circuit brake setup. Front disc, rear drum on most trim levels unless you had the higher towing package which sometimes got rear discs. The brake line routing is fairly straightforward if you know where to look, but it is also one of those jobs where people make unnecessary messes because they don't have a proper diagram and just guess their way through it. The system runs from the master cylinder mounted on the driver side of the firewall, down through the frame rail on the driver side, across the frame on a rubber-hanged crossover tube, back up the passenger side frame rail, and then out to the rear brake lines which snake along the frame and under the bed. The front lines split off at the combination valve which sits just behind the driver side wheel well area and contains the pressure differential switch and proportioning valve. That combination valve is a common failure point on these trucks. The plastic line connector underneath it cracks with age, and you will get a brake warning light on the dash even if the brakes work fine otherwise. I replaced all four brake lines on a customer's 1999 Ram about three years ago. The driver side front flexible line was so corroded at the metal-to-rubber junction that it cracked when I touched it with the flare tool. Nobody expects that kind of failure on a line that looks fine from the outside. The crossover line between the frame rails was completely seized in place. I had to cut it out rather than try to unflare the fittings because the original OEM flares on these trucks tend to roll over themselves when you try to separate them after years of heat cycling. That is something to keep in mind before you buy a tubing kit and plan to reuse the old fittings.
The rear brake lines on these trucks have a tendency to collect road salt and moisture in the bracket clamps along the frame. I found two rear line sections where the corrosion had eaten through the steel from the inside out at the bend points near the frame brackets. The outside looked mostly okay. If you are only replacing one rear line, inspect the entire run. The failure pattern on these trucks is usually not random. It happens at the same stress points every time. For a proper 1999 Dodge Ram 1500 Brake Line Diagram, you can find decent copies in the Chilton or Haynes repair manuals for that model year. Mopar also published factory service bulletins that include line routing diagrams, though those are harder to track down. There are several sites that offer downloads, but most of the free ones online are low resolution copies of the same image that has been recirculated for years. The diagrams show the general routing but they do not indicate fitting sizes or flare angles, which is what actually matters when you are doing the work.
What You Need to Know Before You Start
The brake line fittings on this truck are 3/8 inch for the main runs and 1/4 inch for the front flex lines and the combo valve connections. All of them use 45-degree double flares, which is standard Mopar practice. Do not attempt to use single flare or ISO flare fittings on this vehicle. They will not seat properly and you will have a leak that gets worse every time the suspension cycles. There is no workaround for that. The combination valve assembly is the part that causes the most headaches. It has three line connections on top and the brake warning switch connector on the bottom. When you remove it, the old rubber O-rings inside the port connections harden and crack. Even if the valve itself is fine, new O-rings are worth about eight dollars at any parts counter and they save you from bleeding air into the system later. I always replace them when I pull the valve. The part numbers vary slightly between ABS and non-ABS models, so check your setup before ordering. Avoid the braided stainless line trend on the front lines of these trucks. They look nice, but the steering linkage on the 1999 Ram binds against them when the suspension is at full compression. I have seen it happen. Stick with OEM-style single wall steel lines with rubber flex sections at the wheels. They last just as long and they do not create new problems.
Get the Full Details
The Actual Replacement Process
Start by disconnecting the battery and lifting the front of the truck. Remove the wheels. Then move to the engine bay and disconnect the lines at the combination valve. Have a catch pan ready because there will be residual brake fluid in the lines. Brake fluid will eat paint. Keep a wet rag nearby and wipe everything immediately. Do not let it sit. Next, trace each line from the frame rail to the wheel. Note how the rubber clips hold the lines in place. These clips are plastic and become brittle after twenty-five years. They will break when you remove the old lines. Bring a spare bag of frame clips with you. They cost about four dollars for a pack of ten at NAPA or AutoZone. Not having them means you will end up using zip ties, which is acceptable for a temporary fix but not something you want to leave as the permanent installation. When you run the new lines along the frame, do not overtighten the clips. The lines need a little room to move with the suspension. Snug is enough. If you cinch them down hard, the vibration will eventually work the line loose at the fitting. I learned that the hard way on a personal project truck about ten years ago. Spent a weekend tracking down a slow leak that turned out to be a line that was vibrating against the exhaust crossmember because the clip was too tight.
At the wheel, flare the end of the line before you install it. You can verify the flare with a flare gauge or by comparing it to an existing good fitting. A bad flare is the most common cause of brake line leaks. People rush this step and then spend two hours bleeding the system only to find a puddle of fluid under the truck. Take the time to do the flare correctly the first time. It usually adds about ten minutes to the job per line, which is nothing compared to the time you save on rework.
Bleeding and Final Checks
After everything is installed, bleed the system starting with the wheel farthest from the master cylinder. That is the right rear, then left rear, then right front, then left front. Use a proper bleeding kit or have someone pump the pedal while you open the bleeder valves. Do not just tap the bleeder and hope for the best. Air trapped in the combination valve will make the pedal feel soft for no obvious reason, and you will waste a lot of time chasing it. If you replaced the combination valve, there is a chance you will need to bench bleed it first before installing it. The valve has internal passages that hold air, and if you install it dry, you can get a spongy pedal that does not clear after normal bleeding. Bench bleeding the valve takes about fifteen minutes and uses a small reservoir rig that most auto parts stores will let you borrow if you ask. It is worth doing. Once the system is bled, check the brake fluid level in the master cylinder reservoir and top it off with fresh DOT 3 fluid. Pump the pedal several times with the engine off to build up residual pressure. Then start the engine and check for firm pedal feel. Drive the truck at low speed in a safe area and test the brakes gently. Make sure there is no pulsing or pulling to one side. If there is, you likely have air still in the system or a line that is not routed correctly and is being pulled on by the suspension movement.
The whole job takes about two to three hours for a full set of lines if you are working alone and have the right tools. A professional with a lift and experience does it in about an hour. The parts cost runs roughly forty to seventy dollars depending on whether you go OEM Mopar or aftermarket. It is not an expensive repair, but it is one that requires patience and attention to detail because brake system failures are not forgiving.
