You HAD to make the video long, or else it wouldn't be complete. It helped me retroactively troubleshoot a brake problem I had years ago on a car I no longer have. Nobody else went into the great detail you did.
As far as I can tell, though it's long, this is the only truly comprehensive explanation of all the features of a classic dual-circuit master cylinder with quick take-up.
👍👏👏 my 12 year old son has learned the general concepts from changing the brake pads with me and now he can understand the details behind that general concept. I added this to his home school curriculum so I want to thank u for taking your time to make this video. I don't comment often but I want to thank u to let u know ur efforts are appreciated!
Thank you. A very comprehensive look at master cylinders, albeit older relative to todays technology. A proper understanding of this technology helps with diagnostics on older vehicles. It's my view that this is a definite prerequisite for proper understanding of the newest technology and how newer technology addresses old problems.👍
Thanks James. Glad you found this video valuable. I may do a segment in the future on more modern electro-hydraulic braking systems. Still a lot of the same concepts here, albeit with more electronic controls.
Excellent vid. Best info on the seal cups and then really informative on the quick pick up bore and the differential switch etc too. Really good. Thank you.
A brilliant explanation for any body new to motor engineering and wanting to understand how it actually works. So far ahead of early Master Cylinders , one leak and no brakes.
I experienced total brake loss in a 1960s Pontiac. I stopped the car by downshifting and using the emergency brake. I think this was before they used dual circuit systems.
Well Tommy,it’s not hard to tell that you know your stuff. I’m just a back yard mechanic and often work on brakes.(rotors and pads etc.), but never known the basics of a master cylinder. I thoroughly enjoyed every minute of your video,probably watching it again several times. Looking forward to seeing more of your work, thank you Lester from Canada
Thank you so much!!! Trying to work out why my new master cylinder still has the warning switch engaged.... Needed to understand how that part of the system works. Had to wait to the end, but learned more along the way!!!
Great study of the duel circuit master. I liked the training aids, for example, the cut away master, the drawings, and use of syringes along with the drawings. This was awesome man!
Very informative. My first time trying to bleed brakes { ABS } equipped. I understand closed loop hydraulic principal, what I need is a video on air in the system, all the different places it can be hiding and how to deal with it. From what I've seen on-line I'm not alone
Thanks for the kind words and sticking around for the whole video! It is definitely not a short video, but hopefully you were able to learn some new things about master cylinders. I actually will more than likely make a video in the next few weeks covering wheel speed sensor basics and signal troubleshooting; those are key input signals for your electronic brake control (EBC) systems including ABS, TRAC, ESC, etc.
very good video, I have spent quite some time checking to see if a failed master cylinder can cause brake lock up, after watching your video, the answer is yes.
Really well done. I have been trying to figure out how bleeding my brakes with an open bleeder and a raised hose pushes out more fluid than it pulls back in. It has been hurting my brain. This answers it. Thank you.
The compensator port has nothing to do with pad or break shoe wear. They would as you pointed out relieve unwanted pressure from the brake lines as the temperature of the fluid rose. The amount of stroke required to engage the breaks will be the same whether the pads or shoes are new or brand new. They essentially stay where they are when the brake pedal is released and braking pressure goes to zero. As pads wear you would only see the brake fluid level go down in your reservoir.
In general, I would not use the model of a compressible working body - air - to explain a hydraulic device where the working body - fluid - is incompressible.
I understand how the mechanical linkage between the primary and secondary pistons is present as a fail safe and the springs are only there to return the piston. Those linkages don't come into play when the system has fluid present. During braking the system seems to rely on the primary circuit's fluid being compressed first before it will start to move the secondary piston which will seal off the compensator port and build pressure in the secondary circuit. Put another way, it appears the the primary compensator port is sealed off before the secondary compensator port. That would mean the primary circuit builds pressure and brakes before the secondary circuit. Would this not create a lag in braking between the primary and secondary brake circuit? How did engineers compensate for this in these older master cylinder designs or was this time difference negligible? Thanks!
That is an excellent question. Yes you are correct in the fact that the springs serve as a means of ensuring both pistons return to their state of rest whenever the brake pedal isn't applied, but the spring located in between the primary and secondary piston will transmit some of those pedal forces on the primary piston to the secondary piston before the hydraulic circuit is sealed off. The compensating ports are so small and very close to the piston seals that any small amount of travel from the pistons will seal them off relatively quickly. All of that translates into the pistons both applying equal amounts of pressures in both hydraulic circuits at identical times. You are more than likely correct that there is probably a very small time lag between the circuits, but it is probably incredibly minor; i.e., nothing that we would notice and nothing that would really affect how the vehicle brakes. Also, another factor would be how the hydraulic systems are split, whether they're front to rear, or diagonally split. On modern braking systems, all of that stuff doesn't really matter, but you already know that. Hope this kind of made sense. Things are easier to explain in person, but you know.
@@TimmaethBoy ah yes I did forget the fact that the springs are still in contact with the primary and secondary pistons at all times. So before you begin to overcome the preload of the primary spring and compress it, both pistons will move in tandem. Even once the primary spring begins compressing some force and motion are still translating. It appears the secondary spring is in constant contact at the front of the cylinder? Now it makes me wonder if the spring rates between both springs is the same? I know you can play with timing of mechanisms this way in other systems such as in metal stamping dies with pinning pads, etc. Great video overall and I definitely learned something! You mentioned in the video description that you teach? What do you teach?
@@TimmaethBoy check this animation of a master cylinder out. This is what made me think of my original question. You can see in this animation the time difference but it may be exaggerated for sake of animation. th-cam.com/video/Xk2zGvKfrhc/w-d-xo.html
Yes, the spring up front is in contact with the secondary piston as well. The spring rates are all determined by the engineers so they are more than likely going to be different in size, rate, etc. I teach automotive technology at a local community college for up and coming automotive technicians.
my dodge ram master cyl right now has a coule of bright spots on the bore ....what could have caused that? my brakes are getting hot and I wonder if the pistons are sticking in the bore? thank you
Hi Tommy. Thanks so much for this very informative video! My 2005 Vectra has all round disc brakes and an ABS module. The two braking circuits are diagonally arranged. For many years now the brakes on one circuit have worn significantly faster than those on the other, so I only get 6000 to 10000 miles out of a set of pads (not good!). I have had the flexible brakes hoses replaced (as they can implode internally), and have had the two callipers replaced multiple times. My garage keeps telling me it can't be the master cylinder, as there is no leakage and the brake pedal is hard. Also the brake light doesn't come on, and braking feels normal when driving. Could there be some issue with the master cylinder that could cause this?
You would really need to have the shop do a pressure test on the lines to give more insight as to what's going on. I suspect that the brake circuit causing you issues has residual pressure even with the pedal not applied. You need to have the shop check the pressures at the calipers of each wheel with the brakes released, and then fully applied - key OFF engine OFF, then key ON engine ON (you should see a large increase in pressure with the engine running, but mainly just wanting to see how the pressures behave in both scenarios). If that particular circuit's pressure is controlled by the primary piston of the master cylinder, then you could have a problem where the piston is not retracting fully and creating a slight pressure buildup in the brake circuit even when the pedal is released. What usually causes this is a misadjusted booster pushrod where it's too far out to where it's either: a) partially applying the brakes even with the pedal released (worst case), or b) blocking the compensating/vent ports and not allowing the fluid to expand properly under normal heat cycling of the brake system, which will cause the brakes to begin applying slightly the more the system heats up. You could have an odd problem where the primary piston itself isn't seating fully in the housing, but again, a pressure inspection will give some insight into this. Don't rule out the ABS module as well. The internal valves can stick and cause pressure related issues as well, but once again, it all comes full circle to figuring out what pressures are actually seen at each caliper assembly. It takes a competent shop and some patience to troubleshoot some of the more difficult brake concerns. Best of luck!
Great explanation - thanks. Regarding brake bleeding, I have seen videos describing two different sequences .. 1. open bleeder screw, press pedal, close bleeder screw, release pedal 2. pump brake pedal and hold down, open bleeder screw (pedal drops to floor), close bleeder screw, release pedal Do you have any thoughts on which of these is the better method or if it matters. Thanks
If it's a conventional brake system, then method 2 is a good way of bleeding the system. Do full pedal strokes during the pumping process, 3-5 strokes, hold it, have someone (or you) crack open the bleeder valve for a few seconds (honestly no more than 3 seconds), close the screw, release the pedal, rinse and repeat until clean fluid comes out/no air pockets are present. Most of the time, you start the bleeding procedure from the right (passenger) rear wheel, then the left rear, right front, and left front wheel, but that isn't always the case, so check what the manufacturer recommends for the bleeding order. Also, make sure you are frequently topping off the master cylinder reservoir to ensure the level does not drop below the minimum mark. Unfortunately, you would need a helper with this method and that isn't always possible. The good news is decent quality pressure bleeders are relatively inexpensive and you can bleed brake systems by yourself. Just pressurize the brake system at the master cylinder reservoir to a specific pressure, open the bleed valve until you're satisfied with the fluid coming out, torque it down, and move on to the next wheel/bleed point.
@@TimmaethBoy Thanks so much for the reply. I was mainly curious as to why some folks say to press/pump the brake pedal before opening the bleeder screw and others say to open the bleeder screw before pressing the brake pedal. I guess it is just a matter of personal preference, although pressing the brake pedal first would pressurize the system before letting out the fluid .. maybe that would tend to push any air bubbles toward the bleed point ? Just guessing :)
@@neilbreakwell4500 Your idea about the bubbles is spot on. Building the pressure first will allow any air trapped in pockets to be shot out and some times you need that extra boost to get a bubble to head either down against gravity or out of a junction..
Question‼️ If I understood the lecture properly, the pressure in the Pressure Differential Switch will be different under high loads like panic breaking. Will it cause the switch to close? Did I understand that correctly? How does the computer manage such situations?
And thank you for the video!!! Very easy to understand, covered a lot of mechanics/hydraulics behind it! College level explanation, very in depth and practical. I would love to know if they use the same system on modern vehicles because if something goes wrong on my car I would like to understand what is happening based on how the issue shows.
@@vasylhordiienko7465 No, the pressure differential switch is only there to detect a hydraulic fault in one of the brake circuits. If you have a loss of pressure in one brake circuit, then the pressure differential valve will move because of the pressure imbalances, activating the switch.
I have a 2000 Ford explorer that I deliver mail in and I lost brakes completely. I was going in reverse on a downhill decline. And as slow as it was going I still couldn't stop and had to throw it into Park. So my question is if I still should have had half stopping power how come I didn't? Any answers greatly appreciated.
Sounds like heat fade, i.e., overusing the brakes, especially on inclined surfaces - overheats the brakes to where they no longer work. They have to generate heat to work properly and if they're already too hot, there's no way it can create any additional heat. Usually when this happens, you lose feeling in the brake pedal too - feels stiffer and can't feel the pads biting, at least in traditional brake setups.
I havent watched all of the video yet I paused it . I’m having an issue with brake pressure going away during driving and coming back over night . One day it’s good a few hours later they suck , or I’m driving then I make a run into the store I come back and the brakes feel great . Then I make another stop and then start the vehicle back up again and my brakes suck . I have zero leaks fresh fluid and I have bleed the brakes a few times .
Zabardast cheers from Toronto.....at 25,000 kms 4 years old Mitsubishi RVR losing DOT4 fluid.....but cannot find the leak! Please advise. Also, the stupid Reservoir is inclined for some reason?
If you don't feel any change in your braking performance and you are positive you don't see any leaks from the calipers, bleed screws, HCU, or lines, you may very well have a leaking master cylinder secondary seal. The brake fluid leaks past the seal and into the vacuum booster unit. If that's the case, you're looking at a new master cylinder and booster unit; brake fluid destroys the rubber diaphragm within the booster. A way to verify this is to check and see if there is any wet looking fluid on the back of the master cylinder where it meets up with the booster; sometimes it looks wet underneath there if the seal is leaking, but not always. You can also pull the vacuum hose off at the booster (engine off) and see if it looks like the inside of the hose is wet with fluid. If it is wet, that could very well be brake fluid it's sucking into the intake manifold from the booster because of that seal leak. This is all speculation though and I'm assuming you've traced everything else thoroughly to make sure nothing else is leaking. Also keep in mind that the brake fluid level gradually drops over time as your pads wear - starts full from the factory, then by the time you need new pads, it's somewhere between the halfway mark and minimum in the reservoir.
You're correct; fluid has to fill the pressurizing chamber through the check valve somehow. To do this, they include a cup seal as part of the take-up valve design. Cup seals also act like one-way check valves by allowing fluid to flow from the reservoir chamber into the pressurizing chamber (very slowly), but then seals when there's an increase in pressure (during the take-up process) diverting the fluid from the pressurizing chamber up through the check valve and into the reservoir. It's hard to visualize this without seeing a demo, but I recommend you do a patent search and read the articles on the quick take-up process to get an idea of what I'm talking about. Hope that makes sense.
Hello, I have a question, I have an Audi a4b5 1995 year with abs. A couple of days ago I had a problem with the rear left brake caliper lightly sticking (couldn't feel it while driving) and overheating the wheel until it started to smell. In the process, I lost control of all 4 brakes. The pedal dropped to the floor. If my thinking is right I should have lost control of 2 out of 4 brakes not all of them. Could this be related to a faulty master cylinder maybe with internal leaks? After a cooldown period, the brakes are working fine as usual.
If it were a master cylinder internal leak issue, the problem would be more consistent regardless of temperature. Keep in mind that if the master cylinder had a faulty cup seal(s), it wouldn't be able to properly maintain pressure in the brake system. Initially, I thought maybe a restricted brake line at the L/R caliper could be a possibility (not letting the piston retract properly even when the pedal's released), but that doesn't make sense considering how you said the pedal dropped to the floor and you lost all braking, BUT there's probably more to this. I'm curious if the ABS module on the HCU is interpreting the slower moving wheel as a lock-up condition and attempting to release pressure from the system to "correct" it. This may have been what you're experiencing as a pedal that falls to the floor. I would focus on figuring out why the L/R caliper is partially applying the brakes - check for a restricted line, caliper guide pins seized, caliper piston not retracting correctly, etc. - before continuing further. The ABS module can act really strange if it's not getting proper feedback signals from all 4 wheels. It's really difficult to troubleshoot something like this online, but I would go that route first.
@@TimmaethBoy The rear calipers are very old and rusty. I will change them both. The rear left didn't retract completely but didn't stick hard enough to slow down the wheel because I didn't feel the car driving differently later when the problem arose I stopped and put the car in neutral and tried to push it back and forth on a parking lot it seemed normal. So I doubt the abs trying to let go of the brake was the cause. During the time the problem manifested it self I had to do a bit of driving to get to where I can call a tow truck and if I pumped the pedal I had some braking for a very limited time (seconds) before my foot sank to the floor. There was no pedal shaking like when the abs is operating. The problem is I asked around and everyone is telling me if you overheat or lose even one brake they all fail but by the info, I know about brake circuits, and all I found on the internet there should be a failure of only 2 of the 4 brakes in my case.
@@TimmaethBoy dont know why youtube doesn't let me put a link I disassembled the cylinder. Maybe you can give me your email so I can send you the disassembled picture of the cylinder?
Highly unlikely, unless the pushrod is binding in the backside of the primary piston. Check your brake pedal return spring mechanism and the lever in general to see if anything's binding.
Yes, you can customize a master cylinder and braking system to your particular liking, but that will apply more to vehicles that do road racing/auto-crossing scenarios.
@@TimmaethBoyokay I could get ur point but I like to customize a master cylinder of piston dia 13mm can u suggest me to achieve it. Like the procedures to perform if I get the help it will be so thankful to u..
@@evilmastro1515 The best way is to find someone who specializes in custom brake systems and talk about what you're trying to achieve and go from there. There's probably already products out there with custom piston sizes that may meet your needs. Otherwise, that's a lot of potentially expensive design and machine work to make a custom master cylinder with specific piston/bore diameters, etc.
@@evilmastro1515 Google search for local businesses and call around. You can also do research online as well/ask in forums and they'll point you in the right direction.
You HAD to make the video long, or else it wouldn't be complete. It helped me retroactively troubleshoot a brake problem I had years ago on a car I no longer have. Nobody else went into the great detail you did.
As far as I can tell, though it's long, this is the only truly comprehensive explanation of all the features of a classic dual-circuit master cylinder with quick take-up.
This was the best video yet. I could have listened to you teach for another hour. Thanks
Thanks! Glad you enjoyed it.
👍👏👏 my 12 year old son has learned the general concepts from changing the brake pads with me and now he can understand the details behind that general concept. I added this to his home school curriculum so I want to thank u for taking your time to make this video. I don't comment often but I want to thank u to let u know ur efforts are appreciated!
Appreciate the comment. Thanks a bunch.
Thank you. A very comprehensive look at master cylinders, albeit older relative to todays technology. A proper understanding of this technology helps with diagnostics on older vehicles. It's my view that this is a definite prerequisite for proper understanding of the newest technology and how newer technology addresses old problems.👍
Thanks James. Glad you found this video valuable. I may do a segment in the future on more modern electro-hydraulic braking systems. Still a lot of the same concepts here, albeit with more electronic controls.
Best video on the master cylinder I've seen.
Excellent vid. Best info on the seal cups and then really informative on the quick pick up bore and the differential switch etc too. Really good. Thank you.
Thanks! Glad you enjoyed it.
A brilliant explanation for any body new to motor engineering and wanting to understand how it actually works. So far ahead of early Master Cylinders , one leak and no brakes.
Thanks Rod. Glad you enjoyed it.
I experienced total brake loss in a 1960s Pontiac. I stopped the car by downshifting and using the emergency brake. I think this was before they used dual circuit systems.
Wow thanks for explaining it better than my teacher could’ve
Thanks! Glad you enjoyed it.
great video studying for my A5 currently and I learn a lot from watching this thank you.
You're welcome.
Well Tommy,it’s not hard to tell that you know your stuff. I’m just a back yard mechanic and often work on brakes.(rotors and pads etc.), but never known the basics of a master cylinder. I thoroughly enjoyed every minute of your video,probably watching it again several times. Looking forward to seeing more of your work, thank you Lester from Canada
You're very welcome Lester.
Thank you so much!!! Trying to work out why my new master cylinder still has the warning switch engaged.... Needed to understand how that part of the system works.
Had to wait to the end, but learned more along the way!!!
No one could have explained it better...❤
Thanks!
Great study of the duel circuit master. I liked the training aids, for example, the cut away master, the drawings, and use of syringes along with the drawings. This was awesome man!
Thanks! Glad you enjoyed it.
Outstanding hands on lecture! Well done sir!
Thanks!
Very informative. My first time trying to bleed brakes { ABS } equipped. I understand closed loop hydraulic principal, what I need is a video on air in the system, all the different places it can be hiding and how to deal with it. From what I've seen on-line I'm not alone
I’m learning about masters in school rn this video helped loads in my understanding. THANK YOU!!!
You're very welcome.
43:30 minutes well spent. Studying for the ASE A5 I hope you do more in-depth videos on brakes.
Thanks for the kind words and sticking around for the whole video! It is definitely not a short video, but hopefully you were able to learn some new things about master cylinders.
I actually will more than likely make a video in the next few weeks covering wheel speed sensor basics and signal troubleshooting; those are key input signals for your electronic brake control (EBC) systems including ABS, TRAC, ESC, etc.
very good video, I have spent quite some time checking to see if a failed master cylinder can cause brake lock up, after watching your video, the answer is yes.
Watched this last night very informative thanks
You're welcome.
Well worth watching. Thank you sir.
What a brilliant explanation.
thank you so much! this explanation will definitely help me out with my issue👍
No problem with length of video coz u've just done alot of explaining which is quite in order, THANKS 🙏
Really well done. I have been trying to figure out how bleeding my brakes with an open bleeder and a raised hose pushes out more fluid than it pulls back in. It has been hurting my brain. This answers it. Thank you.
Definitely worth the time. Learned lots. Thank you!
You're very welcome.
Much appreciated! Splendid video, well worth the time.
Thanks! Glad you enjoyed it.
I learned so much from this video
Thank you! Nice explaination only one thing not confirm, we consider primary unit to right side which is in contact with push rod
That is correct. The primary piston is in contact with the push rod from the booster.
Thanks a lot for making such an informative video . Job well done
This was a great video 🎯👍👌🔥
Such a great video thank you for sharing your knowledge
Thanks King.
Great video mate very good info 👍
Thanks!
Gr8T Video Appreciated Tommy Man
The compensator port has nothing to do with pad or break shoe wear. They would as you pointed out relieve unwanted pressure from the brake lines as the temperature of the fluid rose. The amount of stroke required to engage the breaks will be the same whether the pads or shoes are new or brand new. They essentially stay where they are when the brake pedal is released and braking pressure goes to zero. As pads wear you would only see the brake fluid level go down in your reservoir.
very interesting demonstration
Gracias. Por. Subir. Tu video desde Bolivia te. Saludos
Fantastic Explanation!😀
Thanks so much for this amazing video outlining how the tandem brake system works. I love it champ 👍 good on you and keep it up
Thanks! Glad you enjoyed it.
Does the brake pedal has a return spring?
Hi,Great video & thank you
You're welcome. Glad you enjoyed it.
Great information....thanks a lot
You're welcome.
I learnt alot, thank you
very nice explanation thanks so much||
Great video . Thanks 😊
You're very welcome.
Thanks Tommy. You're cool.
In general, I would not use the model of a compressible working body - air - to explain a hydraulic device where the working body - fluid - is incompressible.
Thank you very much.
I understand how the mechanical linkage between the primary and secondary pistons is present as a fail safe and the springs are only there to return the piston. Those linkages don't come into play when the system has fluid present. During braking the system seems to rely on the primary circuit's fluid being compressed first before it will start to move the secondary piston which will seal off the compensator port and build pressure in the secondary circuit. Put another way, it appears the the primary compensator port is sealed off before the secondary compensator port. That would mean the primary circuit builds pressure and brakes before the secondary circuit. Would this not create a lag in braking between the primary and secondary brake circuit? How did engineers compensate for this in these older master cylinder designs or was this time difference negligible? Thanks!
That is an excellent question. Yes you are correct in the fact that the springs serve as a means of ensuring both pistons return to their state of rest whenever the brake pedal isn't applied, but the spring located in between the primary and secondary piston will transmit some of those pedal forces on the primary piston to the secondary piston before the hydraulic circuit is sealed off. The compensating ports are so small and very close to the piston seals that any small amount of travel from the pistons will seal them off relatively quickly. All of that translates into the pistons both applying equal amounts of pressures in both hydraulic circuits at identical times.
You are more than likely correct that there is probably a very small time lag between the circuits, but it is probably incredibly minor; i.e., nothing that we would notice and nothing that would really affect how the vehicle brakes. Also, another factor would be how the hydraulic systems are split, whether they're front to rear, or diagonally split. On modern braking systems, all of that stuff doesn't really matter, but you already know that.
Hope this kind of made sense. Things are easier to explain in person, but you know.
@@TimmaethBoy ah yes I did forget the fact that the springs are still in contact with the primary and secondary pistons at all times. So before you begin to overcome the preload of the primary spring and compress it, both pistons will move in tandem. Even once the primary spring begins compressing some force and motion are still translating. It appears the secondary spring is in constant contact at the front of the cylinder? Now it makes me wonder if the spring rates between both springs is the same? I know you can play with timing of mechanisms this way in other systems such as in metal stamping dies with pinning pads, etc.
Great video overall and I definitely learned something! You mentioned in the video description that you teach? What do you teach?
@@TimmaethBoy check this animation of a master cylinder out. This is what made me think of my original question. You can see in this animation the time difference but it may be exaggerated for sake of animation.
th-cam.com/video/Xk2zGvKfrhc/w-d-xo.html
The animation is definitely exaggerated, but it is an excellent animation to show the concept behind a tandem master cylinder.
Yes, the spring up front is in contact with the secondary piston as well. The spring rates are all determined by the engineers so they are more than likely going to be different in size, rate, etc.
I teach automotive technology at a local community college for up and coming automotive technicians.
my dodge ram master cyl right now has a coule of bright spots on the bore ....what could have caused that? my brakes are getting hot and I wonder if the pistons are sticking in the bore? thank you
Hi Tommy. Thanks so much for this very informative video! My 2005 Vectra has all round disc brakes and an ABS module. The two braking circuits are diagonally arranged. For many years now the brakes on one circuit have worn significantly faster than those on the other, so I only get 6000 to 10000 miles out of a set of pads (not good!). I have had the flexible brakes hoses replaced (as they can implode internally), and have had the two callipers replaced multiple times. My garage keeps telling me it can't be the master cylinder, as there is no leakage and the brake pedal is hard. Also the brake light doesn't come on, and braking feels normal when driving. Could there be some issue with the master cylinder that could cause this?
You would really need to have the shop do a pressure test on the lines to give more insight as to what's going on. I suspect that the brake circuit causing you issues has residual pressure even with the pedal not applied. You need to have the shop check the pressures at the calipers of each wheel with the brakes released, and then fully applied - key OFF engine OFF, then key ON engine ON (you should see a large increase in pressure with the engine running, but mainly just wanting to see how the pressures behave in both scenarios).
If that particular circuit's pressure is controlled by the primary piston of the master cylinder, then you could have a problem where the piston is not retracting fully and creating a slight pressure buildup in the brake circuit even when the pedal is released. What usually causes this is a misadjusted booster pushrod where it's too far out to where it's either: a) partially applying the brakes even with the pedal released (worst case), or b) blocking the compensating/vent ports and not allowing the fluid to expand properly under normal heat cycling of the brake system, which will cause the brakes to begin applying slightly the more the system heats up. You could have an odd problem where the primary piston itself isn't seating fully in the housing, but again, a pressure inspection will give some insight into this.
Don't rule out the ABS module as well. The internal valves can stick and cause pressure related issues as well, but once again, it all comes full circle to figuring out what pressures are actually seen at each caliper assembly. It takes a competent shop and some patience to troubleshoot some of the more difficult brake concerns. Best of luck!
@@TimmaethBoy Thanks very much for the detailed reply Tommy! Will have to see if I can find a garage capable of doing it.
Great explanation - thanks.
Regarding brake bleeding, I have seen videos describing two different sequences ..
1. open bleeder screw, press pedal, close bleeder screw, release pedal
2. pump brake pedal and hold down, open bleeder screw (pedal drops to floor), close bleeder screw, release pedal
Do you have any thoughts on which of these is the better method or if it matters.
Thanks
If it's a conventional brake system, then method 2 is a good way of bleeding the system. Do full pedal strokes during the pumping process, 3-5 strokes, hold it, have someone (or you) crack open the bleeder valve for a few seconds (honestly no more than 3 seconds), close the screw, release the pedal, rinse and repeat until clean fluid comes out/no air pockets are present. Most of the time, you start the bleeding procedure from the right (passenger) rear wheel, then the left rear, right front, and left front wheel, but that isn't always the case, so check what the manufacturer recommends for the bleeding order. Also, make sure you are frequently topping off the master cylinder reservoir to ensure the level does not drop below the minimum mark.
Unfortunately, you would need a helper with this method and that isn't always possible. The good news is decent quality pressure bleeders are relatively inexpensive and you can bleed brake systems by yourself. Just pressurize the brake system at the master cylinder reservoir to a specific pressure, open the bleed valve until you're satisfied with the fluid coming out, torque it down, and move on to the next wheel/bleed point.
@@TimmaethBoy Thanks so much for the reply. I was mainly curious as to why some folks say to press/pump the brake pedal before opening the bleeder screw and others say to open the bleeder screw before pressing the brake pedal. I guess it is just a matter of personal preference, although pressing the brake pedal first would pressurize the system before letting out the fluid .. maybe that would tend to push any air bubbles toward the bleed point ? Just guessing :)
@@neilbreakwell4500 Your idea about the bubbles is spot on. Building the pressure first will allow any air trapped in pockets to be shot out and some times you need that extra boost to get a bubble to head either down against gravity or out of a junction..
@@rivit7615 Thank you. Always wondered why two different methods are described in different videos.
Great video and highly informative however, you can have four wheel disk brakes so when you say rear caliper you aren’t wrong in doing so
Question‼️
If I understood the lecture properly, the pressure in the Pressure Differential Switch will be different under high loads like panic breaking. Will it cause the switch to close? Did I understand that correctly? How does the computer manage such situations?
And thank you for the video!!! Very easy to understand, covered a lot of mechanics/hydraulics behind it! College level explanation, very in depth and practical. I would love to know if they use the same system on modern vehicles because if something goes wrong on my car I would like to understand what is happening based on how the issue shows.
@@vasylhordiienko7465 No, the pressure differential switch is only there to detect a hydraulic fault in one of the brake circuits. If you have a loss of pressure in one brake circuit, then the pressure differential valve will move because of the pressure imbalances, activating the switch.
I have a 2000 Ford explorer that I deliver mail in and I lost brakes completely. I was going in reverse on a downhill decline. And as slow as it was going I still couldn't stop and had to throw it into Park. So my question is if I still should have had half stopping power how come I didn't? Any answers greatly appreciated.
Sounds like heat fade, i.e., overusing the brakes, especially on inclined surfaces - overheats the brakes to where they no longer work. They have to generate heat to work properly and if they're already too hot, there's no way it can create any additional heat. Usually when this happens, you lose feeling in the brake pedal too - feels stiffer and can't feel the pads biting, at least in traditional brake setups.
I havent watched all of the video yet I paused it .
I’m having an issue with brake pressure going away during driving and coming back over night .
One day it’s good a few hours later they suck , or I’m driving then I make a run into the store I come back and the brakes feel great . Then I make another stop and then start the vehicle back up again and my brakes suck .
I have zero leaks fresh fluid and I have bleed the brakes a few times .
Thank you
You're very welcome.
Zabardast cheers from Toronto.....at 25,000 kms 4 years old Mitsubishi RVR losing DOT4 fluid.....but cannot find the leak! Please advise. Also, the stupid Reservoir is inclined for some reason?
If you don't feel any change in your braking performance and you are positive you don't see any leaks from the calipers, bleed screws, HCU, or lines, you may very well have a leaking master cylinder secondary seal. The brake fluid leaks past the seal and into the vacuum booster unit. If that's the case, you're looking at a new master cylinder and booster unit; brake fluid destroys the rubber diaphragm within the booster.
A way to verify this is to check and see if there is any wet looking fluid on the back of the master cylinder where it meets up with the booster; sometimes it looks wet underneath there if the seal is leaking, but not always. You can also pull the vacuum hose off at the booster (engine off) and see if it looks like the inside of the hose is wet with fluid. If it is wet, that could very well be brake fluid it's sucking into the intake manifold from the booster because of that seal leak.
This is all speculation though and I'm assuming you've traced everything else thoroughly to make sure nothing else is leaking. Also keep in mind that the brake fluid level gradually drops over time as your pads wear - starts full from the factory, then by the time you need new pads, it's somewhere between the halfway mark and minimum in the reservoir.
Hi, how does the fluid replenish into the system across the check valve? As fast as I know a check valve is a one way flow ? Thanks.
You're correct; fluid has to fill the pressurizing chamber through the check valve somehow. To do this, they include a cup seal as part of the take-up valve design. Cup seals also act like one-way check valves by allowing fluid to flow from the reservoir chamber into the pressurizing chamber (very slowly), but then seals when there's an increase in pressure (during the take-up process) diverting the fluid from the pressurizing chamber up through the check valve and into the reservoir.
It's hard to visualize this without seeing a demo, but I recommend you do a patent search and read the articles on the quick take-up process to get an idea of what I'm talking about. Hope that makes sense.
Simple displacement of fluid
Hello, I have a question, I have an Audi a4b5 1995 year with abs. A couple of days ago I had a problem with the rear left brake caliper lightly sticking (couldn't feel it while driving) and overheating the wheel until it started to smell. In the process, I lost control of all 4 brakes. The pedal dropped to the floor. If my thinking is right I should have lost control of 2 out of 4 brakes not all of them. Could this be related to a faulty master cylinder maybe with internal leaks? After a cooldown period, the brakes are working fine as usual.
If it were a master cylinder internal leak issue, the problem would be more consistent regardless of temperature. Keep in mind that if the master cylinder had a faulty cup seal(s), it wouldn't be able to properly maintain pressure in the brake system.
Initially, I thought maybe a restricted brake line at the L/R caliper could be a possibility (not letting the piston retract properly even when the pedal's released), but that doesn't make sense considering how you said the pedal dropped to the floor and you lost all braking, BUT there's probably more to this.
I'm curious if the ABS module on the HCU is interpreting the slower moving wheel as a lock-up condition and attempting to release pressure from the system to "correct" it. This may have been what you're experiencing as a pedal that falls to the floor. I would focus on figuring out why the L/R caliper is partially applying the brakes - check for a restricted line, caliper guide pins seized, caliper piston not retracting correctly, etc. - before continuing further. The ABS module can act really strange if it's not getting proper feedback signals from all 4 wheels.
It's really difficult to troubleshoot something like this online, but I would go that route first.
@@TimmaethBoy The rear calipers are very old and rusty. I will change them both. The rear left didn't retract completely but didn't stick hard enough to slow down the wheel because I didn't feel the car driving differently later when the problem arose I stopped and put the car in neutral and tried to push it back and forth on a parking lot it seemed normal. So I doubt the abs trying to let go of the brake was the cause. During the time the problem manifested it self I had to do a bit of driving to get to where I can call a tow truck and if I pumped the pedal I had some braking for a very limited time (seconds) before my foot sank to the floor. There was no pedal shaking like when the abs is operating. The problem is I asked around and everyone is telling me if you overheat or lose even one brake they all fail but by the info, I know about brake circuits, and all I found on the internet there should be a failure of only 2 of the 4 brakes in my case.
@@TimmaethBoy dont know why youtube doesn't let me put a link I disassembled the cylinder. Maybe you can give me your email so I can send you the disassembled picture of the cylinder?
can a failed master cylinder cause a pedal to not return after being pressed
Highly unlikely, unless the pushrod is binding in the backside of the primary piston. Check your brake pedal return spring mechanism and the lever in general to see if anything's binding.
Is is possible by us to customize the masters cylinder?
Yes, you can customize a master cylinder and braking system to your particular liking, but that will apply more to vehicles that do road racing/auto-crossing scenarios.
@@TimmaethBoyokay I could get ur point but I like to customize a master cylinder of piston dia 13mm can u suggest me to achieve it. Like the procedures to perform if I get the help it will be so thankful to u..
@@evilmastro1515 The best way is to find someone who specializes in custom brake systems and talk about what you're trying to achieve and go from there. There's probably already products out there with custom piston sizes that may meet your needs. Otherwise, that's a lot of potentially expensive design and machine work to make a custom master cylinder with specific piston/bore diameters, etc.
@@TimmaethBoy but I don't know how to find the person
@@evilmastro1515 Google search for local businesses and call around. You can also do research online as well/ask in forums and they'll point you in the right direction.
Mass balance
What is this off of?
Older GM vehicle. I don't have the specifics other than that.
all you had to do was just install the rod and push
Air quotes are too woke, shut it down.
Witchcraft