There usually are no diagrams. The original steel lines are installed onto the chassis before the body was in place on the assembly line. It is not practical to install new lines the same way.
You also have to decide if you are going to make your own custom lines or piece together pre-manufactured sections with unions. I find if you buy a bulk roll of steel line, because it was round up into a coil, it is very hard to make a nicely-centered double-flare on the end. Also, given the time it takes to make those flares, it is much faster and easier to buy sections from the auto parts store.
Almost all cars and light trucks use 3/16" line. You can buy it in lengths from about 12" to four or five feet. It is even available now with an electro-plated coating to resist rusting out longer. If you are careful, you can bend it by hand without kinking if you wrap it around your thumbs. You can also buy a bending tool. I have been doing this for over thirty five years, and never needed that bending tool.
It is common practice to leave the old lines in place, and use nylon tie straps to attach the new lines to the old ones to hold them in place. When you cannot route the new line around something or through a hole in the frame, there are always other places you can go, but avoid running any brake line close to hot exhaust parts. Also keep the number of high spots to a minimum. Those are easy places for air to get stuck, making it harder to bleed out.
Here are some useful tips:
Remove and replace just one line at a time. Every once in a while we read here that someone removed them all, then forgot which one goes where. Minivans and front-wheel-drive cars usually use a split-diagonal brake hydraulic system. As such, they have two brake lines going to the rear. Minivans and pickup trucks also can have a wide range of loading, from empty to full, meaning there can be a big variety in the percentage of load on the rear, and the percentage of braking power needed in the rear. To adjust for that, they have a height-sensing proportioning valve near the rear axle. Add to that, if the vehicle has four-wheel anti-lock brakes, there will be two different lines going to the two rear wheels. GM is one of the exceptions. To reduce cost, they often modulate the two rear wheels together even though only one is locking up. Those will still have just one line going to the rear.
When you connect the lines and tighten the nuts, those are made of very soft metal. Use a flare-nut wrench, aka "line wrench". Those grip the nut on four sides instead of just two. If your old lines are real rusty, they will also be rusted to the old nuts. You can just twist them off since they are being discarded, or you can cut the line off right next to the nut, then pound on a six-point socket, and use a ratchet to unscrew the nut.
The double-flare has a little give to it so it will form to the sealing surface you are bolting it to. If you make your own double-flares, the final step is to use the tool to push the metal down and form the sealing surface. Do not get carried away with how tight you make the tool. You want to leave a little crush zone for the final assembly. Along with that, if you are going by trial and error, like I do, add the first piece of line, but do not fully tighten the nut until you are sure that's where it is going to stay. I start at the front, then after all the bends have been formed, I see how much more line I need, then add the next one. Some people piece them all together, then figure out which one to remove so they can put a slightly shorter or longer one in its place to get the total length right. Only after that has been figured out do you fully tighten each nut. That is when the double-flare will mold itself to the fitting, and seal the best. If you decide to remove a line later, when you install it somewhere else, you may have to really tighten the nut to get it to seal.
When it comes time to bleed the system, I only use gravity-bleeding. Loosen the cover on the master cylinder's reservoir so no vacuum builds up in there that would impede the flow of the brake fluid. It might take five or ten minutes for fluid to show up at one wheel. When it does, close that bleeder screw, and wait for the next one to start flowing. Keep an eye on the reservoir so it doesn't run empty. When all four bleeders are closed, "irritate" the brake pedal a little by hand. That will push any sticking air bubbles into the wheel cylinders and calipers. Open each bleeder once more for a couple of seconds to pop those bubbles out. Too many people think they have to resort to pedal-bleeding with a helper. I have not done that since the 1980's, but if you feel you must, never, never, ever push the brake pedal more than half way to the floor. Crud and corrosion build up in the lower halves of the bores where the pistons do not normally travel. Pushing the pedal over half way, whether bleeding or when surprised by a sudden leak, runs the rubber lip seals over that crud and can rip them. That causes a slowly-sinking brake pedal, and that often does not show up for two or three days.
My most important tip is to not allow any type of petroleum product anywhere near where there is supposed to be brake fluid. That includes engine oil, transmission fluid, power steering fluid, and penetrating oil. Do not even use penetrating oil to try to loosen the old line nuts. Petroleum products are not compatible with the rubber used for brake parts. That rubber will swell and become mushy. In the master cylinder, the lip seals will grow past the fluid return ports and block them so the brakes cannot release. The only fix for oil in the brake fluid is to remove every part that contains rubber that contacts the brake fluid, and replace them after flushing and drying the steel lines. That includes the calipers, wheel cylinders, rubber flex hoses, master cylinder and the bladder seal under the cover, the combination valve, height-sensing proportioning valve, and if the vehicle has anti-lock brakes, the hydraulic controller. The cost of that repair can easily exceed the value of the vehicle.
There is a good chance you will not get the bleeder screws loose on the wheel cylinders. Do not put a lot of effort into working on them. New wheel cylinders are pretty cheap, so just replace them. When you are done bleeding the system, wash the inside of the bleeder screws with brake parts cleaner, dry them, then pop on the rubber caps that came with them. That keeps water out. Bleeder screws that rust tight do so mostly from water going down the center hole.
If you have to push the brake shoes around or remove them, do not get any grease on the linings or the drums' friction surface. Once hot, that grease will soak in and cause squealing. Cast iron is porous so the grease will soak into that too. Once hot, you will never be able to get that grease out. If you wash any contamination off with brake parts cleaner before those parts go through a heat cycle, they should be okay. Professionals even wash their hands before installing pads and shoes to avoid getting fingerprint grease on them.
If you remove the rear shoes, there are some problems common to GM vehicles to look for. Each shoe rides on three "lands", or raised spots on the backing plate. Other manufacturers bend tabs over on the shoes to create a sliding surface that wears very little. GM does not do that, so the edges of the shoe frames grind into those lands. If grooves form on them, they can prevent the shoe from moving under light pedal pressure, and in extreme cases they can cause a shoe to stick and stay applied. If those grooves are real deep, the backing plate must be replaced. If they are not too bad, you may be able to file them smooth. Regardless, part of a professional brake job is to lubricate those lands with a special high-temperature brake grease. One trade name used to be "Rusty Lube", but there are many others. Don't use regular axle grease. Brake grease contains molybdenum disulphide and it will not travel. It stays where you put it.
Another problem specific to GM is they used wheel cylinders that clipped to the backing plates with a ring with two fingers. It was real common for the hour glass-shaped holes to rust away and allow the wheel cylinders to turn enough that the pistons popped out leading to a sudden loss of brakes. Eventually they came up with an improved design that uses the same bolt-on wheel cylinders that every other manufacturer uses. You have to replace the backing plate with that new design, and install the standard wheel cylinder. For a long time you could only get those new backing plates from any GM dealer, but last I heard, they do not want to sell them anymore. They were available from auto parts stores later.
If you do need to replace the wheel cylinders, pop an old one apart, then read the diameter on the inside of one of the lip seals. There were usually two to four different diameters used on the assembly line for different applications. Using new wheel cylinders with the wrong diameter will cause easy rear-wheel lockup, or too little rear braking power. The diameters go by 1/16".
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Friday, March 19th, 2021 AT 12:35 PM
