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How to Replace a Brake Master Cylinder in Your Car (Bleed Brakes)


one, two, three, four! Rev up your engines! It’s time for the Scotty Kilmer Channel,
is your brake pedal sink to the floor when you step on it, then stay tuned on
this frosty morning because I’m going to show you how to fix it, if brake pedals
start sinking, that means there’s a leak in the system somewhere, so get a jack,
and pull off all four wheels to see if it’s leaking at any of the wheels, pull
off the tires and look at the brake system, this is completely dry so it’s
not leaking, and the back wheel brakes were dry too, so they’re not leaking, and
since none of the rubber lines are leaking either, that leaves the brake master cylinder, the brake master cylinder often leaks
inside itself, so you lose pressure and the pedal goes to the floor, now to
remove the brake master cylinder, you need a special wrench like this, that has a
little hole in the top, so it fits over the line, it’s a 10 millimeter on this
Honda, you place it on top of the bolt and then whack it to get it loose, then
the rest you can just spin with your hand to get the line off, and off it
comes, then of course remove all the other brake lines from the master
cylinder too, then get a socket wrench, it’s 12 millimeters on this Honda, and take
the two bolts off that hold it on, then you just wiggle it, until it comes off,
and in this case we know the master cylinder is bad because you can see it’s
been leaking on the back of the seal all the crud is there, now here’s a
mechanic’s tip, buy a brand new master cylinder, don’t buy a rebuilt one, I’ve
had problems with rebuilt over the years, and I don’t use them anymore, now you
just get the new master cylinder, put it in place on the two bolt holes, it just
slips right on, and then you put the washer and the bolt on that holds it in
place, and get them nicely tight with your socket wrench,
and now comes the tricky part, you bleed the air out of the system,
first pour the brake fluid in, and then put the brake lines on, but only put them
on loosely, so they’re not tight, now being a professional mechanic, I have
power tools to bleed out brake systems, but hey, you can use a giant screwdriver
and do a good job all by yourself, you just get your giant screwdriver, put one end
on the brake pedal, push it down and jam it against the seat, then push the seat
up as far as it goes, that’s the same as pushing your foot on the brake and it
builds up pressure, then with the pedal push down, tighten the lines up as tight
as they go, just keep tighten them till you can’t
tighten them anymore, then once all the lines are tight, take the screwdriver out,
then you loosen the brake lines again, and stick the screwdriver in, and push
the seat up again, and just repeat this process four or five times and all the
air will be out of the master cylinder, and now we’ve got a nice hard brake
pedal, that stops on a dime, so the next time your brake pedal is
giving you that sinking feeling, fix it yourself, and remember if you’ve got any
car questions visit Scotty Kilmer.com

100 thoughts on “How to Replace a Brake Master Cylinder in Your Car (Bleed Brakes)

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  2. Absolutely love this video!! Looks like i do need to change the master cylinder in the mini seem that theres no leaks at all and still hahe a full reservoir but still have a slack pedal.

  3. Old video but still a question. I have no leaks and bled all 4 brakes. Still feels spongy and car pulls to the left when I brake hard.. is this typical for a faulty master brake cylinder?

  4. Scotty, I'm doing a master cylinder on a 93 Buick Regal. This one has 4 ports on the MC. Is it the same procedure? Loosen and tighten all 4 at the same time?

  5. Hello,
    I have a 03 Lincoln ls that does not accelerate above 25mph. I thought it was a bad TPS so i installed a new one but I still have this problem. speaking with an employee at AutoZone gave me a list of problems that it could be and one of them is the brake master cylinder. In your opinion (or anyone eslse thats reading this) could a bad brake master cylinder causes the car to not accelerate properly?

  6. Thanks! You are very informative and I really enjoyed your style. Also my dad was one if this countries first Army Rangers.

  7. Scotty I love you videos, but I've always done this job by bleeding each individual brake in a sequence from closest to furthest. (Always had an assistant) I also bench bleed the master before installing it. Your way looks soooo much simpler, I'm wanting to try it but I am a bit scared as this car is my main transportation. (You own one, 94 Celica) Much love bro!

  8. Your the best and my most favorite car guru on the web! I have one question. Why does the big line/(back breaks) not air out as fast. My front breaks are cleared but the smalled resevour big line hasnt aired out. Is there a leak in yhe system you think?? My brake light is on.

  9. Having issues with a 2000 Chevy suburban, replaced master cylinder and bleed all 4 wheel twice but im still not getting a hard brake pedal, im gonna try this method and see how it works

  10. It was scary today, I was coming home but when I pressed on my break peddle it didnt go down to the floor or feel squishy… it just didnt stop me as fast as it normally does and it was very noticeable. Is that the break master cylinder? I checked the reservoir and for leaks down by the peddle… but everything seems good no leaks or anything… I'm very confused and dont know who to call to help. Because I didn't want to drive it at all if that's the case, people could get hurt. Any help?

  11. You’re the freakin best dude. You have true real world knowledge with cars AND you know how to make a perfect diy YouTube video!

  12. Doesnt air get reintroduced to MC when you crack open the lines? Not a mechanic, just genuinely curious. I have MC to bleed in a 94 Sonoma at the moment and wanna do it right. Love your videos man! Keep it up!

  13. My master was rusted to the booster so had to replace it all. I ensed up breaking the evap purge thingy so looking for one of them now. Lol fords. .

  14. Hey Scotty, I have a sierra and I clipped a curb with the rear wheel (slid in snow). A little further down the road I hit the brake and it almost went to the floor but got hard right at the end of pedal travel. Now it seems only the front brakes are working and the pedal still almost goes to the floor.
    I checked the rear drum brake on the wheel that hit and it is fine as are the rest of the brakes (bone dry no leaks or damage) so I thought it was the master cylinder. Changed the master cylinder and it made no difference. I think it might be a stuck solenoid in the abs system but no abs light is on in dash. Any thoughts?

  15. Hey mr good morning we have 3500 ram diesel I have the same problem make petal Blake lose pressure can you tell me more ideas because we don’t have lecks in the lines Thanks

  16. i remember doin a master cylinder on a 1996 accord with dad cause the brakes dragged. We bled the master by pumping the brakes and cracking the lines

  17. To save making a mess doing this inside the engine bay with fluid squirting everywhere, put in in a plastic container on the work bench and bleed it out there pushing the piston with a blunt fat phillips head screwdriver or such. Then carry it with about half full carefully and install while keeping it upright as possible. Then attach lines and tighten and bleed to each wheel nipple to remove the small amount of air trapped and pass through fresh fluid..

  18. Hello Scotty question I have a 2001 ford crown Vic. When I was driving. Down hill I hit the brake close to the floor before it stopped and than I backed up. On a dip. Hip. Lot. The brake. Seem like. It was going to stop. Help help. My mechanic bleed the. Lines out the other day. The test is when I go home tonight

  19. Nice video but most vintage vehicles new master cylinders don't exist,sometimes not even rebuilt ones but I have always found kits that work after the reusable parts spent some time in an ultrasonic cleaning tank.Get bleeder valves with check valves too if your master cylinder has bleeder valves on it.

  20. what an amazing and very informative video, now i can work on my brakes alone. mr scotty I wish I do my automotive apprenticeship with you, your years and years of experience is very helpful even giving us those ideas and techniques that was not taught at school, so amazing!

  21. Not so Scotty brother! Your method does not work for master cylinder bench bleed. Not even close. I’ve been doing this for 50 years as well… This is the first time I’ve seen anything from you that was not correct! Simply does not work!

  22. That beats bleeding it from each caliper which I would have done had I not watched this video. Thanks Scotty!

  23. Just did it and it works. It took awhile for the fluid to show at the lines, but eventually fluid and air both started to come out. I continued to pump and bleed until I saw no more air and the front calipers no longer seem to drag. Now, I’m sure I have some air in the lines from disconnecting them from the master cylinder as the brakes seem a little soft, but it is drivable and I will do a complete bleed at the wheels another day.

  24. i love your videos! You've helped us so much!

    I'm a little confused, how come you didn't bleed the air using the bleeder valves at the calipers?

    Also, we're you a Ranger???I

    Thank you for all you're hard work!

  25. In my 1989 CHEVY SILVERADO truck I have to press the brake pedal about 3 times before my truck moves in drive, What is the problem??

  26. Thank you Scotty Kilmer, you saved me, I didn't bleed the master cylinder and bleeded the wheels and the pedal became spongy thanks to your video (unlike others that use pressured bleeders that an average person like wouldn't have) I resolved the issue alone without having a second person to pump pedal or unmount master cylinder for the so called bench bleeding. Your the best because you think of the average person who might have fancy tools mechanics have, thank you.

  27. Scotty, would a leak at either the wheels or the master cylinder also cause the parking brake light on the dash to come on?

  28. Hey Scotty! I have a2011 f150 STX my brake fluid is going low and there’s no leaks in the calipers. I just watched a old video bout u changing out the master cylinder do you think I have the same issue ? Brake pedals goes down further as the fluid goes low in the reservoir.

  29. Is there some reason you can't just use a standard open ended wrench rather than a special brake wrench, or whatever it's called?

  30. Anyone have any tips for getting the brake lines reattached? Mine are determined to cross thread, and it's driving me crazy!!

  31. Awesome video Scotty! Is it necessary to bench bleed the cylinder or this is fine? I'm working on 1999 honda Accord 4 cyl with ABS.

  32. Changed a leaking master cylinder on my Nissan wingroad now every time I hit the brakes no matter how lightly it reacts as emergency brakes my mechanic doesn't seem to know how to fix this,help!

  33. Hey scotty my problem is i bleed the brake lines and for some reason brake fliud is still coming out the bleeder screw i change all calippers and still doing the same thing do you think is the master cilynder also when i come to a complete stop the car shakes only when i hold downe the brake pedal any sugestions thanx in advance….

  34. If I bench bleed the master cylinder and then install it on the car; do I need to bleed it again when I connect the brake lines to the master cylinder?

  35. Thank you Scotty for confirming my belief that you don't have to run bleeding lines back into the reservoir . I was pretty sure you could just leave the lines loose and place a towel underneath to catch any fluid .

  36. what about bench bleeding ? should I bleed the brakes after this master cylinder bleed ? thanks scotty for your great info.

  37. This video actually caused me to make a costly mistake, time-wise. It should have a disclaimer that this method is not for all master cylinders. I replaced a master cylinder on a Ford Escape and followed your method for bleeding it. After the pedal pressure was still nonexistent despite multiple repetitions, I investigated further and found out that the type of master cylinder I had needed to be either bench-bled or else bled on the car BEFORE hooking the lines up to the master cylinder using a bleeder kit with hoses that fed back into the reservoir. By attempting to bleed the master cylinder as shown in this video, I actually introduced a LOT of air into the system which required me to have to go back and re-bleed all four wheels. Needless to say, I'm a bit miffed.

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