Motorsport Plumbing Systems: Bleeding Brakes
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Bleeding Brakes
12.18
| 00:00 | If you're planning on taking your car to the track, modifying the brake system plumbing, or working on a race team, bleeding the brakes are one of the most commonly used and fundamental skills required. |
| 00:11 | It's an extremely important skill to have and while it's critical to carry it out correctly for a properly functioning brake system, the good news is it's also very simple to do. |
| 00:21 | In a motorsport context, brake bleeding is a maintenance item that needs to be carried out regularly, with many high level teams bleeding the brakes after every session, regardless of whether an issue has been reported or not. |
| 00:34 | What we're trying to do when bleeding the brakes is remove the degraded fluid from the system and replace it with fresh fluid. |
| 00:41 | Alternatively, we could be filling the system with fresh fluid for the first time and making sure the system is full after making a change to the plumbing that might have resulted in some spillage. |
| 00:52 | The process gets its name from the fact that it requires the opening of the system at different points in order for the old fluid or air to be bled out. |
| 01:02 | As we remove the old fluid or air, we need to top up the fluid reservoir to ensure the system remains full and new fluid replaces the old. |
| 01:11 | There are multiple different approaches to brake bleeding with specific tools and processes available to help either speed up the job or reduce the number of people required to carry it out. |
| 01:21 | In this section we'll go through the tried and true approach that doesn't require any investment in any special tools. |
| 01:28 | To do it we'll need some new brake fluid that's compatible with the existing fluid and suitable for the application, a helper who can operate the brake pedal during the process, a spanner the correct size for the bleed nipples on your calipers and a bleed bottle with suitably sized flexible clear hose. |
| 01:47 | Lastly, we should always have some clean rags and brake clean on hand to clean up any small drips of brake fluid as we go and to clean up more thoroughly at the end, remembering that most types of brake fluid are corrosive to paint, so we want to quickly clean any spilt fluid up with a rag and brake clean as soon as they happen. |
| 02:07 | You can get specific brake bleeding bottles but any old soft drink bottle can work just as well. |
| 02:13 | The important thing is that the hose we're going to use is clear so we can monitor the state of the fluid as we go. |
| 02:19 | The end of the hose that attaches to the bleeder nipple also needs to be a tight fit in order to prevent any leakage and mess. |
| 02:27 | If the clear hose you have isn't the correct diameter, you can get a suitable short length of rubber hose that slips over the clear hose and locates well on the bleed nipple. |
| 02:37 | This can help the problem as the rubber hose can often accommodate for a wider range of diameters while still sealing. |
| 02:44 | The bleeding occurs at the brake calipers, which will have bleed nipples fitted to them. |
| 02:48 | In order to successfully carry out the bleed, the nipples need to be positioned at the highest point on the caliper. |
| 02:55 | Keep in mind that some calipers have a single nipple, while others will have two. |
| 03:00 | In a single piston caliper there will only be a single bleed nipple. |
| 03:04 | If there are two nipples and one is on the top and the other is on the bottom, we can ignore the lower nipple. |
| 03:09 | This is to allow the brake caliper to be mounted upside down relative to its current orientation and is redundant in its current position. |
| 03:18 | Anytime we carry out the bleed process, we want to begin as far away from the brake master cylinders as possible and work backwards towards them. |
| 03:27 | Depending on the way our system is plumbed, this may or may not be important, but in many cases this is the most efficient order to carry out the process of removing air bubbles from the system. |
| 03:37 | Regardless, it's a good idea to use this rule of furthest to closest to help keep track of what we've done so far. |
| 03:44 | In this case, where we have a right hand drive car, we want to begin on the left rear caliper, moving to the rear right, then the left front and finally the right front. |
| 03:54 | If we have calipers that have inner and outer bleed nipples on the top of the caliper, applying the same principle, beginning with the outside before moving inside. |
| 04:04 | Moving on to the process itself, step one is to jack up the car, place it on axle stands and remove the wheels. |
| 04:10 | This will give you better access to the bleed nipples on the calipers. |
| 04:13 | We can now remove the protective rubber caps from the bleed nipples if fitted and put them aside. |
| 04:19 | If there aren't any caps, then it's important to give the nipples a quick wipe with the rag and brake clean to remove any dirt or debris. |
| 04:26 | For step two, we should check that the brake fluid reservoir that supplies the master cylinders has sufficient fluid in it and top it up if required. |
| 04:35 | It should be at least at the full mark. |
| 04:37 | Step three is to move to the furthest brake caliper to begin the bleed. |
| 04:42 | Remember to begin at the outermost nipple if there's more than one bleed position on the top of the caliper. |
| 04:47 | In step four, we can fit the ring end of the spanner onto the bleed nipple, followed by the bleeder hose. |
| 04:54 | Make sure the other end of the hose is sitting in the bleeder bottle. |
| 04:57 | If our bottle has a hook, then we can usually hook it onto the suspension somewhere in order to free up a hand throughout the process. |
| 05:05 | For step five, we ask our assistant who's sitting in the driver's seat to press down on the brake pedal. |
| 05:11 | Throughout this process, it's critical to have clear communication between ourselves, the bleeder and the assistant. |
| 05:17 | This is because to properly carry out the bleed, we need to work in a synchronised manner. |
| 05:22 | The process will be the same for every bleed cycle. |
| 05:26 | The person who leads the communication is always the bleeder, but clear communications in both direction is required. |
| 05:33 | The process always begins with the bleeder saying down. |
| 05:36 | This is the signal for the assistant to pump the brake pedal three times. |
| 05:40 | On the final pump, they keep a firm pressure on the brake pedal. |
| 05:44 | They should maintain this pressure until they're told otherwise. |
| 05:47 | At this point, the bleeder will open the brake nipple using the ring end of the spanner. |
| 05:52 | It only needs to be opened a small amount and we don't want to open it any more than is necessary. |
| 05:58 | Usually a quarter of a turn will be sufficient and you'll know you have it open when the fluid begins to flow. |
| 06:04 | When the fluid flows out through the nipple, the brake pedal will start to drop for the assistant. |
| 06:08 | They should keep consistent pressure on the pedal and allow it to drop. |
| 06:12 | As the fluid flows out through the clear hose, we'll get a chance to check its condition. |
| 06:16 | If it's been overheated, it'll be a darker colour than the original clear to yellow shade it is when it's new. |
| 06:24 | If there's air in the system, you'll be able to see bubbles suspended in the fluid that'll flow out through the hose. |
| 06:30 | Another telltale sign of air being evacuated is that you'll often hear a slight clicking sound and this is the air bubbles flowing out of the caliper and through the hose. |
| 06:39 | Once the brake pedal has dropped as far as it'll go, the assistant should say down. |
| 06:44 | The fluid will stop flowing through the bleed hose at this point. |
| 06:47 | This is when the bleeder should close the nipple. |
| 06:50 | The nipple doesn't need to be tightened hard. |
| 06:52 | Over tightening can easily damage the nipple and the seat at the bottom of the nipple, or even snap it off. |
| 06:58 | It only needs a light tug to ensure the seat is properly closed. |
| 07:03 | Once the nipple is closed, the bleeder says up. |
| 07:06 | This lets the assistant know that they can release the pressure off the brake pedal, allowing it to naturally return up. |
| 07:12 | Once the pedal has returned all the way up, the assistant says up. |
| 07:17 | This is the signal to the bleeder that the bleed cycle is complete. |
| 07:20 | The order of this is critical. |
| 07:22 | The bleed nipple must be closed before the assistant releases pressure on the brake pedal. |
| 07:27 | This is why the two way communication is so important. |
| 07:30 | We repeat step five of the process until the fluid we're bleeding from the system is clean and contains no air bubbles or the brake pedal firmness stops improving. |
| 07:40 | This might mean repeating this process four to five times before moving on to the next bleed position. |
| 07:46 | The other thing to be aware of throughout the process is that the brake fluid reservoir never runs dry at any point. |
| 07:53 | If this is allowed to happen, air will be drawn into the master cylinder inlet which will require an even more extensive bleeding process to be started again. |
| 08:02 | This means keeping an eye on the reservoir and topping it up as required. |
| 08:06 | It's normal to check this after about four to five bleed cycles but the capacity of every system is different and this is something that you'll quickly get a feel for as you go through the bleeding process. |
| 08:18 | Step six is to move to the next bleed nipple and repeat step five. |
| 08:22 | This may either be on an inboard bleed nipple on the same caliper or the next caliper in the sequence. |
| 08:28 | Remember we're always moving from the furthest point away from the master cylinder back towards the closest. |
| 08:34 | Continue to move around the car until all calipers and relevant bleed nipples have been bled. |
| 08:40 | At this point, as long as all the air is removed from the system, all the fluid coming out looks to be in good condition and the brake pedal quality feels good, then we're done with the bleeding. |
| 08:51 | If you're bleeding the brakes to improve the pedal stiffness due to boiling the brake fluid, then the pedal feel should have significantly improved with it feeling firmer. |
| 09:01 | Once we're happy the bleeding process is complete, we can move towards wrapping things up with step seven. |
| 09:07 | Going around and checking that all the bleeder nipples are sufficiently tight. |
| 09:11 | If you don't know what this should feel like, you can check the manufacturer's torque specs, but after a while you'll naturally get a feel for it. |
| 09:19 | Next we move around each corner of the car with our rag and a can of brake clean, giving each nipple and any other areas of the calipers or suspension that could have brake fluid on them a spray and wipe. |
| 09:31 | We can then refit all the rubber duffs caps. |
| 09:34 | Step eight is to check our fluid level in the master cylinder reservoir and this should be topped up to the max line. |
| 09:40 | Step nine is to refit all the wheels, drop the car onto the ground and check the brake pedal again. |
| 09:46 | If everything feels good, we're ready to go out and test the car on the road or the track. |
| 09:51 | We should start out a little conservatively on the first brake applications to make sure everything feels good before moving on to harder stops. |
| 10:00 | One additional note here is that with some cars fitted with ABS systems, there's another step required in bleeding the process. |
| 10:08 | This is due to a small amount of fluid that is kept separate within the ABS pump while it's not operating. |
| 10:14 | In systems that have this, if the bleed is carried out without the pump operating, then the fluid won't be flushed out during the bleeding process. |
| 10:22 | Cars with this style of pump will have a recommended procedure where the ABS pump is cycled during the bleed. |
| 10:29 | In some cases this is only possible using a specialist tool to force the pump to run during the bleeding process and you should check the official recommendations for your make and model if you aren't sure if this applies. |
| 10:42 | This can be either with the dealer or an official servicing documentation. |
| 10:46 | The reason for this bleed is also an important factor when it comes to this ABS issue. |
| 10:51 | If we're bleeding the system to remove air due to boiling the fluid, in all likelihood these bubbles will be within the calipers or at least very close to the calipers. |
| 11:01 | In this case it's unlikely that the fluid within the pump needs to be bled at all and simply carrying out the standard bleeding process we just covered will be sufficient. |
| 11:11 | However in the case where we're completely flushing the system, then it is important to cycle the pump during the bleeding process. |
| 11:19 | In the end, if you aren't sure, it always pays to check with the manufacturer. |
| 11:23 | To summarise, bleeding the brakes is a critical process that ensures hydraulic pressure is effectively transferred from the master cylinder to the brake caliper and therefore the brakes are operating correctly. |
| 11:34 | The key aim of bleeding the system is to remove old or degraded fluid, which has absorbed moisture or been overheated and contains air bubbles. |
| 11:43 | Or alternatively, to ensure a modified or new system is full of fluid with no air bubbles. |
| 11:49 | While the bleeding process can vary somewhat depending on the layout of the brake system, the core steps are generally the same and involve working with an assistant who pressurises the system using the brake pedal while we bleed the damaged fluid from the nipples on the caliper. |
| 12:04 | Remember to begin as far from the master cylinder as possible and work towards it, always keeping the fluid in the reservoir topped up and quickly cleaning any spillage of the corrosive brake fluid. |
