A “Quick Fix” Can Prevent Major Problem! Clean the Bleeder Plugs on the Calipers Using Parts Cleaner!

The bleeder plug that you touch when changing the brake fluid or cleaning the caliper is a small part that drains the fluid from inside the caliper. However, just a little bit of care can be the difference between a troublesome problem later on or not. After loosening the bleeder plug, don't forget to spray it with parts cleaner or flush it with tap water.

Normal bolts and bleeder plugs have different roles

This is an example of rust on the brake hose and bleeder plug due to long-term storage. The coil-type guard of the brake hose is corroded, which is a common pattern for outdoor storage vehicles. The bleeder cap is barely still intact, but it is cracked due to aging, and its waterproof performance must have been significantly degraded.

Bleeder caps are not only available as a genuine part, but may also be sold as a general-purpose item by some accessory manufacturers. These are made by Daytona and come in sets of four and are available in black as well as red, blue, and other color versions.

Daytona has also released a bleeder plug made of rust-resistant stainless steel for both practicality and customization. The screw size of the genuine bleeder plug is M7 x P1.0, M8 x 1.25, M10 x 1. It's one of three 25's, so make sure you know the screw size of your own car when you replace it.

Drain bolts for engines and radiators and bleeder plugs for brake calipers are different from bolts that only hold the parts in place, preventing the contents from leaking while allowing them to be attached and removed periodically. Furthermore, drain bolts and bleeder plugs have different roles. The drain bolt is purely a plug, while the bleeder plug is both a plug and a passage.

On top of that, the handling of these bolts requires different attention than normal bolts. They must be tightened firmly in order to prevent brake fluid from leaking inside the caliper, but it is not enough to just tighten them as hard as you can. If you remove the bleeder plug when changing the brake fluid or overhauling the caliper, you will notice that it has a tapered tip. You will also notice that the hexagonal part does not touch the caliper when the plug is tightened.

The function of the plug of the bleeder plug is established by the fact that the tip of the plug and the back of the female thread on the caliper side are both tapered, and the two are in contact. The mechanism is completely different from the oil drain bolt where the gasket at the base of the bolt contacts the oil pan and the tension applied to the threaded part prevents loosening and prevents leakage. The hexagonal part of the plug does not need to be in contact with the caliper because the tip of the plug seals it, so there is no gasket in the plug itself. In contrast, the brake hose banjo bolt has gaskets on both sides of the banjo to take advantage of the tension and frictional force acting on the threads when the bolt is tightened.

Another important role of the bleeder plug is to serve as a pathway, with the basic premise of not leaking brake fluid. As you know, air mixed in the pathway is a great enemy to brakes, and it is necessary to release the air after the fluid is injected. The bleeder plug is a stopper, but it also serves as a passage to release the air. The banjo bolt is a complex shape with a vertical hole in the center and a horizontal hole near the tip.

When the bleeder plug is loosened slightly and the brake lever is held while there is a small gap between the plug and the tapered contact area of the caliper, the air in the caliper is pushed out through this gap and passes through the horizontal hole, then through the vertical hole and out the top of the plug. This is the reason why the plug is tightened while holding the lever, because if the lever is released, air may be sucked in through the top of the plug when the master cylinder piston returns.

If the plug is loosened too much when bleeding air, brake fluid may seep out from the gap between the threads, so the theory is to keep the amount of loosening to a minimum. However, since fluid pressure from the lever exits from a place where it can easily escape, it will flow to the side hole with less resistance before the threaded part. If you want to prevent the fluid from leaking from the plug thread, you can apply grease to the area where the plug meets the caliper.

By the way, with the lateral hole of the plug ahead of the threaded part, the torque when tightening the plug is critical. Because even though the plug at the tip contacts the caliper, the hex part of the bolt doesn't reach the caliper. There is a risk of crushing the horizontal hole if it is tightened with excessive torque. The tightening torque is about 5Nm. The specified tightening torque for the bleeder plug is about 5Nm, which is easily over-torqued by using a long-handled spectacle wrench. The hexagonal part does not touch the caliper, and even if the tapered part touches the caliper, the response is not so firm, so it is easy to put a lot of force. Be careful not to overtighten.

Bleeder plugs allow not only air but also brake fluid to pass through them.

This is an example where the horizontal hole at the plug tip is completely blocked. This means that no air or fluid can come out of the loosened plug when the brake lever is pressed. White corrosion marks remain on the threads, but it's fortunate that the hexagonal part didn't get damaged or break off in the process.

When I poked the hole with the carburetor jet cleaning needle, the rust crumbled and went through. If the owner had checked the condition of the brakes regularly, he would have noticed this before it got so bad, but he must have been very careless.

Whereas locking pliers make contact with the bolt at two or three points, the blade of the nut twister makes contact at six points, making it easier to apply force and harder to crush hollow bleeder plugs. To prevent rusty plugs from breaking, let's apply good heat with a heater and then spray lubricant before working.

Care must also be taken in handling during brake maintenance. As mentioned above, over-torquing is strictly prohibited, and in addition, dirt and corrosion in the plug must be taken into consideration.

When you change the fluid or overhaul the caliper and bleed the air, not only air but also brake fluid will come out from the tip of the plug. Brake fluid is damaging to the paintwork, so it is important to prevent it from sticking to the wheels and fenders, and if it does, it must be washed off with water as soon as possible.

And the same care needs to be taken with the bleeder plug itself. Genuine parts for commercial vehicles are made of steel and have a plated surface, so there is no need to worry about damaging the paint. However, since brake fluid is highly hygroscopic, it can cause rust due to moisture attracted by driving in the rain or during storage. To make the situation worse, the bleeder cap is not installed. The plug has a hole in the center, which leads to a horizontal hole near the tip. When the plug is tightened, the tapered tip prevents rust and moisture from entering the caliper. When the plug is tight, the tapered tip prevents rust and moisture from entering the caliper, but they can reach the bottom of the threaded part through the vertical and horizontal holes. What will happen if the brake fluid that adheres to the inside of the plug during the air bleeding process is left untouched and combines with moisture to develop into rust?

First, the passage in the plug will be blocked. Even though there is fluid in the master cylinder and caliper and the brakes work, you may not be able to drain the fluid in the caliper by connecting the drain hose, loosening the bleeder plug, and squeezing the lever. By poking the plughole with a thin needle tool for carburetor cleaning, spraying parts cleaner to clean the vertical hole part, and then injecting anti-corrosion lubricant and waiting for it to penetrate the horizontal hole, you may be able to open the passage and allow the air and fluid in the caliper to drain. Of course, once you're able to get the air out, that's not all you need to do. The rusted bleeder plug will be pulled out and replaced with a new one as soon as possible.

It is important not to leave behind highly hygroscopic brake fluid

Insert the long nozzle of the parts cleaner into the plug hole and spray. The brake fluid that has accumulated in the hole will flow backwards and scatter, so cover the tip of the plug with a rag before spraying. This one push will prevent corrosion afterwards. This is a very simple job and should be done without fail.

The accumulated parts cleaner can be blown by air, or it can be sucked up with tissue paper or a thin rag. When this process is finished, make sure to put the bleeder cap on.

In addition, as the rust progresses and corrodes, the hexagonal part can be stripped. Spanner wrenches and 12-point adjustable wrenches are easy to strip, so 6-point sockets are recommended. If the bolt is seriously tarnished, use locking pliers for normal bolts, but if the hollow bleeder plug is tightly clamped, it may be deformed. Use a socket with a blade that can break into the damaged bolt.

If it gets worse and the bleeder plug snaps off at the bolt, that's the worst part. If you have a TIG welder, you can weld another bolt to the end of the broken plug and pull it out. If you have a TIG welder, you can weld another bolt to the end of the broken plug and pull it out. The heat from the weld on the plug will hopefully cause it to unstick from the caliper, but it's a big deal if it gets this far.

In order to avoid causing such a troublesome situation. It is important that no brake fluid is left inside the bleeder plug and that no moisture is allowed in from the outside. It is a good idea to clean the plugs with parts cleaner after changing the fluid or bleeding the air. It is a basic rule to clean the plugs with parts cleaner after changing the fluid or bleeding the air, but when doing so, use a long nozzle to aim at the hole in the plug and inject the cleaner without fail. This hole is a stop hole, so if you spray the entire plug evenly, the fluid in the hole may not be pushed out. Then, suck up the remaining parts cleaner by twisting a rag or tissue paper thinly, or blow it off with an air blowgun.

When the rubber bleeder cap has hardened to a tickle with age, or has flown off somewhere before that and is gone, always install a new cap. Even if you've gone to the trouble of cleaning the brake fluid in the plugs, it won't do you any good if rainwater is still getting in all over the place. It's not an expensive part, so if you can pinch it with your fingers and it's not flexible, replace it even if it's not cracked.

The role of bleeder plugs is important and delicate, and they can cause unexpected problems. But it is easy to prevent it. By always wearing the bleeder cap and cleaning the brake fluid left in the plug with parts cleaner during brake maintenance, the bleeder plug will always be in good condition.