The metal line for the rear brakes runs along the left frame rail, across a rear cross-member to the rubber hose that drops down to the axle. Unscrew the line fitting at the bracket that holds the rubber hose to the cross-member. At the front, look for a nice clean spot on the metal line with no rust. You'll need to cut the line in that area, slide on a threaded line fitting, then make a double flare on the end of the line. Run new metal line between the two fittings. The easiest way is to buy manufactured steel line with the fittings already installed. You might have to buy multiple lines and connect them with the special connector fitting. All you have to do is tell the person at the parts store how long the replacement line needs to be. They will supply the lines and fittings. If you can't find a clean section in the original line, you can replace it all the way up to the valve. If you have rear wheel anti-lock brakes, the fitting should be a standard size that comes already installed on pre-manufactured line. If you don't have anti-lock brakes, the line will go into the back of the combination valve. This fitting is usually very large. In the past, we reused the fitting with the new line, but now you can buy a six inch section of line with the new proper size fitting already installed. If you piece together multiple sections of line, you will not have to make your own double flares.
You don't have to remove the old line if you don't want to. You can also use it to tie up the new line. If the old line goes over the fuel tank, you can try pushing the new line over the tank too, or you might be able to go around it. The line must be anchored well to prevent it from vibrating. Excessive vibration will cause the metal to work-harden and crack. It must also not be in close proximity to the exhaust system. If you push the new line over the tank, cover the end with something to prevent dirt from getting into it. When bends in the line are necessary, don't just grab it with your hands and twist it into a bend; put your thumbs end to end on the line and gently massage it while putting pressure on it. This will prevent the line from kinking as it bends. You can use a bending tool also but they aren't necessary if you're careful.
Before you start removing the old line, use a stick between the seat and the brake pedal to hold the pedal down about an inch or two. That will prevent brake fluid from draining out while you do the repair. After the line is replaced, tighten all the splices and connections except the rear one by the rubber hose. This connection is one of the highest and is a convenient place to bleed the hydraulic system. Start by gravity bleeding. Just remove the stick from the brake pedal, and loosen one cap on the master cylinder so it won't build up a vacuum that prevents the brake fluid from flowing. If fluid doesn't start dripping by the rear hose in a few minutes, stroke the brake pedal just an inch or two a few times to start the fluid flowing.
Once fluid drips from the rear connection, lightly tighten it, then have a helper push the pedal down about one third of the way, or use your stick again. Open the rear fitting and watch the air bubbles come out. Release the pedal and repeat the procedure a few times until no more air bubbles come out. If you move the pedal slowly, any air bubbles will float up and stay near the rear hose connection. If you push the pedal quickly, you risk pushing air bubbles down to the wheel cylinders. That will require the time-consuming bleeding at each rear wheel and the risk of snapping off rusted bleeder screws.
ONE WORD OF WARNING! During this entire service and bleeding, NEVER, NEVER, EVER push the brake pedal more than half way to the floor. The pistons in the master cylinder don't normally run in the bottom half of their bores so scale and corrosion build up there. Pushing the pedal over half way runs the seals over that crap and rips them. Torn seals will result in a pedal that sinks slowly to the floor when you hold steady pressure on it.
Don't let the master cylinder run dry. That will introduce more air in the system and make it harder to bleed. One reservoir cap should be loose so the vacuum doesn't pull fluid and air back up when you release the pedal. When you're not bleeding the system, leave the reservoir caps on tight. Brake fluid loves to suck moisture out of the air which will lower the boiling point of the fluid and promote corrosion.
If you need to push the rubber seals back into the reservoir caps, be sure your fingers are clean. Any grease or other petroleum product on your hands will contaminate the brake fluid. Petroleum contamination, even just a little, will cause rubber seals to swell. The only proper repair is to replace every rubber hose and every component containing a rubber seal which includes front calipers and rear wheel cylinders. All steel lines must be flushed out and dried. That's a real expensive repair.
You can also buy steel brake line in bulk and make your own double flares. Bulk line comes coiled up. Because of the stresses from the bend, double flares tend to end up slightly off-center. It takes some practice to get it right. If you do make a double flare, don't crimp it real tight in the final step. Leave a little cushion so the flare can conform to the seat in the fitting when you tighten it down the final time. Don't coat any connections with grease or oil in an attempt to prevent future rust. Petroleum products can seep into the threaded connections over time and contaminate the fluid. Mopar spray white lube is nice because it will set up and not migrate into the fittings. Rustproofing works well too but is messy to remove when service is required.
Don't refill the master cylinder all the way unless the front disc brake pads were recently replaced. When replacing the pads, the pistons must be pushed into the calipers. The fluid behind the pistons goes back up into the reservoir and can overflow causing peeling paint and a mess on the floor. When you're done, hold steady pressure on the brake pedal for a minute. If it slowly sinks to the floor, either a fitting is leaking or there's a ripped seal in the master cylinder. A rebuilt master cylinder is usually less expensive than a rebuild kit and comes with a warranty. During bench-bleeding and when pedal-bleeding on the truck, you CAN push the pedal all the way to the floor with a new master cylinder because there's no corrosion in it yet. If you do try to rebuild your old master cylinder, don't use anything that can scratch the coating in the bore. The master cylinder is made of aluminum which corrodes very easily. The anodized coating prevents this from happening. Any sandpaper, picks, or other sharp tools will scratch the coating. Only use rags and cleaning chemicals.
Tuesday, June 16th, 2009 AT 3:36 PM