Brake bleeding rear calipers?

Doesn't matter. Most vehicles of this type use a "split-diagonal" hydraulic system, meaning the left rear brake is on the same hydraulic circuit with the right front brake. The two rear brakes are on different circuits.

There won't be much bleeding involved when replacing calipers, however, you must be careful to not allow the brake fluid reservoir to run empty. If it does, you may get enough air in the lines to require extensive bleeding. I do have a simple trick to address that. Also, of it looks like it will take some time between removing the old calipers and when the new ones get bolted on, a simple trick to prevent the brake fluid from running out of the reservoir is to place a stick between the driver's seat cushion and the brake pedal to hold the pedal down about an inch. Gravity won't be strong enough to pull brake fluid past the lip seals in the master cylinder.

Once the brake work is done, loosen the cap on the reservoir to prevent vacuum from building up that would impede the free flow of fluid. Open the bleeder screws, then wait for brake fluid to start dripping from them. When one is dripping fluid, close that bleeder screw and wait for the next one to do the same thing. If no fluid drips out after a few minutes, it may be necessary to "irritate" the brake pedal by hand a few times to get the flow started. Press it only an inch or two, no more.

Your rear calipers do not incorporate the parking brake mechanism. They use the more simple, common sense design that is the same as the front calipers. As such, after compressing the pistons so you can fit in the new pads, those pistons have to be adjusted out by repeatedly pressing the brake pedal. When you do that, be very careful to not press it more than halfway to the floor. By about the first year in the life of master cylinder, crud and corrosion build up in the lower halves of the bores where the pistons don't normally travel. Anything that allows the pistons to travel too far will run the rubber lip seals over that crud and can rip them. That results in a slowly sinking brake pedal, and that commonly takes two or three days to show up. Press the brake pedal halfway repeatedly until it becomes firm, indicating both calipers are in adjustment.

Open each bleeder screw once more to expel the few remaining air bubbles that may have washed into the calipers. During this service, keep checking the level in the reservoir.

As the brake pads wear, the pistons gradually work their way out of the caliper housings to keep the pads in adjustment. Brake fluid fills in behind the pistons, so as the brakes wear, the level goes down in the reservoir. This is one fluid we never top off during other routine services, such as oil changes. When the pistons are pushed back in to make room for the new pads, that pushes the brake fluid back up into the reservoir. If fluid had been added previously, now it will overflow creating a mess. Brake fluid eats paint too, so it must be washed off right away.

What this means is as part of the bleeding process, if the front pads are worn and will need to be replaced in the near future, don't fill the reservoir to the "full" line. You can fill it that full if the front pads are fairly new.

When doing anything with brake fluid, be extremely careful to not allow any type of petroleum product to get into the brake fluid or touch any rubber parts that contact brake fluid. Even a little oil stain on your fingertips can result in a very expensive repair. This includes engine oil, transmission fluid, axle grease, penetrating oil, and power steering fluid. Professionals even wash their hands with soap and water when working with rubber parts to avoid contaminating them with fingerprint grease.

Let me know how the job turns out and if you have other questions.

No. There's no reason air should be in those lines. What you CAN do if you want to, is once the rear brake work is done and everything is operating properly, you can open the front bleeder screws to remove some of the old brake fluid. This is just a preventive maintenance thing to get any absorbed moisture out of the system. Look at the fluid level in the reservoir before you start. Here again, don't let the reservoir run empty. I like to drain out enough so the level gets very close to empty so there's less diluting the new fluid with the old stuff. Next, look at the thickness of the remaining linings. If they look like new pads, with a lot of life left, it's okay to fill the reservoir closer to "full". If the linings are rather thin and will need to be replaced soon, leave the reservoir level on the lower side so there's room for the brake fluid when the caliper pistons get pushed back in later.

It doesn't take much to get all the fluid replaced for any one brake. Small 8-ounce bottles of new fluid are only about 2" in diameter. If you drain the old fluid into one of those, an inch of fluid is enough to get the job done. Another way to tell is old brake fluid will be dark, possibly almost black. That's a normal result of being hot many times. New brake fluid will be clear or light yellow. When you see that show up, that circuit has most of the old brake fluid bled out.

When I'm done bleeding, I like to wash out the center of the bleeder screw with brake parts cleaner. Fluid left in there leads to a rusted and plugged screw. They come from the factory with rubber caps, also to keep them clean and dry. When a bleeder screw gets rusted tight, often to the point we snap them off, it's because they developed rust through the screw's center hole, not through the threads.

To elaborate on my comment about my trick if the reservoir runs empty, that starts to put air in the lines, but if you catch it quickly enough, you don't have to bleed at the wheels. In fact, bleeding air all the way down to the wheels that way should be avoided if at all possible if the vehicle has anti-lock brakes. More on that in a minute.

As long as the air has only gone down the lines a few inches, add some new, fresh brake fluid to the reservoir. A half inch of fluid is enough for now. Press the brake pedal slowly only about an inch, hold it for a few seconds, then let it spring back up rapidly. Do that a number of times. If you have a helper do that, you can watch what's happening in the reservoir. As the brake pedal just begins to move down, a few small air bubbles will pop out of the "replenishing" port and float out of the brake fluid. When the brake pedal is released, a few more bubbles will appear and float away. Each time the brake pedal is pressed, some air in the master cylinder gets pushed out through the replenishing port, until the pistons move far enough to block that port. That's when the brake fluid ahead of the pistons is trapped and forced to be pushed down to the wheels to apply the brakes. Some air in the master cylinder and lines will be pushed down the lines too, but by doing this slowly, the brake fluid goes down and the air floats back up. When the brake pedal is released quickly, brake fluid rushes back up into the reservoir and washes some air back up there with it. Some air is expelled each time you do this. As a result, the fluid level in the reservoir will go down. Keep an eye on it so the level doesn't drop too far again.

You may also be able to accomplish the same thing by just adding brake fluid to the reservoir, then letting the vehicle sit for a day or two. This takes longer, but over time, brake fluid will seep down to replace the air. I have a '70s muscle car that gets stored for the winter. Each spring the reservoir is empty, which is actually pretty common for stored vehicles. All I do is add new brake fluid, then go out and drive it. The brake pedal is a little soft at first, but with each application, some of the air comes out. It only takes a few miles before the pedal feels normal.

The reason we want to avoid bleeding at the wheels when the vehicle has anti-lock brakes is that air has to travel through the hydraulic controller. Most have multiple chambers where that air can pool and not flow to the wheels. You need a scanner to command the ABS Computer to open two valves to let that air be expelled, then it can be bled out at the wheels. The scanners have instructions telling you exactly which bleeder screws to open and when. The procedure usually takes two people, one to work the bleeder screws and one to press the brake pedal when told to do so. This step with the scanner only adds about a minute or two to the rest of the job, but when it's necessary, there's usually no way around it. A few models don't have this problem, but it is very common on most of them.

Yup. That's the only method I use. If you want to speed things up, you can push the brake pedal by hand a few times, but not more than an inch or two. Loosen the cap on the reservoir to prevent vacuum from developing. When you release the pedal, the rubber lip seals in the master cylinder can be strong enough to cause brake fluid to be pulled back, rather than taking a new bite of fluid. When that happens, air gets sucked in through the open bleeder screw. That just makes more work to bleed that air back out.

I don't mean to confuse the issue even more, but for the benefit of others researching this topic, I should point out a little-known problem that can be caused by pedal-bleeding and / or pushing the brake pedal over halfway to the floor. This applies mostly to GM vehicles, mainly to their front-wheel-drive models, but it can show up any time. That has to do with a valve that trips inside the master cylinder. It is very effective at stopping the loss of brake fluid when a leak develops. Unfortunately, it isn't spring-loaded and will not reset on its own. You lose two brakes. One front and the opposite rear brake. One symptom is the pads on one front brake are worn out and grinding metal-on-metal, while those on the other side look like brand new. You might see a little wiggle in the steering wheel when the brakes are applied. This is a common cause of needing new brakes every 10,000 to 20,000 miles.

The problem is besides tripping that valve to block a leak, it also trips when the brake pedal is pushed over halfway, AND there's unequal pressure developed in the two hydraulic circuits. Obviously, if there's a leak in one circuit, no pressure can build up while it does in the other circuit. This also occurs when pedal-bleeding the brakes. An open bleeder screw prevents pressure from building. Even the manufacturer's service manuals say to "push the brake pedal to the floor". That is guaranteed to trip the valve. Then they say to start bleeding with a specific wheel, usually the right rear, but even that is nonsense. That implies that valve will not trip if a leak develops at that wheel, which we know is not true. This valve can even be tripped after a routine brake job when the pedal is pumped to run the pistons out of the caliper housings to adjust them. One side will always have a little more friction and build its pressure after the other side has done so. That little unequal pressure can trip the valve. This heartache and frustration is easy to avoid by just using gravity-bleeding.

Service manuals often specify bleeding in a specific order, but that is nonsense. As I mentioned earlier, if bleeding a certain brake first prevents a valve from tripping in the master cylinder, it also won't trip to do its job if a leak develops in that circuit. Some mechanics like to bleed the left front brake first because it's the fastest way to get one circuit completely free of air. Some like to start at the right rear because it is the longest run and will get the most air out of the system, leading to a solid brake pedal sooner. I always start bleeding with the brake I'm standing closest to. The point is it doesn't matter. You're over-thinking this and making it much more complicated than it needs to be.

You want the air out. You don't want to trip a valve, if your vehicle even uses that, and you don't want to cause damage to seals in the master cylinder, so simply never press the brake pedal more than halfway to the floor. You don't want to cause damage to rubber brake parts, so don't allow even a hint of petroleum product to get into brake fluid.

You only have to bleed the rear brakes because the calipers were replaced and they're full of air. No air entered the front brakes as long as the reservoir never ran empty, so any draining there is for preventive maintenance and can be done any time.

Here's the way I would handle this in the shop. Rebuilt calipers are at hand, ready to install. Remove the rear wheels. Use a large flat-blade screwdriver to pry the pistons into the caliper housings. Observe the brake fluid level in the reservoir. Loosen the banjo bolt holding the rubber flex hose to that caliper. Unbolt the caliper from its mount, then continue removing the banjo bolt. Remove that caliper and let it drain in a drain pan. Service or replace the rotor, as necessary. Prepare the new pads. (More on that in the next paragraph). Install the new caliper with new pads. Bolt on the flex hose with new copper washers. (If two new washers don't come with the rebuilt caliper, I reuse the old ones, but the one between the hose and caliper gets flipped over. It will form new ridges to help it seal when it's tightened). Open the bleeder screw and remove its rubber cap, if it came with one. Do the same thing on the other side while keeping an eye on the first one. If you see brake fluid start to drip from the first bleeder screw, close that one, then finish up on the second brake. When both have been gravity-bled, snug the bleeder screws, then work the brake pedal by hand until it gets solid. Open each bleeder screw once more so the few remaining air bubbles will come out. (If you skip that step, you'll never know it. That's not nearly enough air to cause a low or mushy brake pedal). Wash the brake fluid off the calipers, especially inside the bleeder screws, with Brake Parts Cleaner in a spray can. When dry, install the rubber caps on the bleeder screws. (No need to get excited if those are missing. They fall off from a lot of vehicles). Reinstall the wheels / tires. Refill the reservoir with new brake fluid to the level you observed earlier. Press the brake pedal by foot repeatedly to be sure it is high and solid, while never pushing it further than normal or no further than halfway to the floor. This is where I'd drain brake fluid from the front calipers if the vehicle was on a hoist. When done, fill the reservoir again to the level you started with, and wash the calipers and bleeder screws. If I'm doing this in my driveway at home, I'd test-drive the vehicle first in case there is a problem, I'd know for sure it had to do with the rear brakes. Working with the front brakes before the test-drive just adds one more variable in case there is a problem. Test-drive a good two to five miles with multiple stops to seat the new pads to the new or machined rotors. Include at least one or two very aggressive stops to warm the pads.

That's what we're here for. I'm here about this time every day. I expect to hear good news. Let me know if you have more questions, and how this turns out.