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Soft Squishy Brakes Hard to Stop How to Diagnose Brake Master Cylinder Leak

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Created on: 2021-08-19

Len breaks down the master cylinder, giving you an insider look at the components, and where leaks may develop, so that you can diagnose your own brake master cylinder and replace it if necessary!

Come on, stop. The brakes are really bad on this thing. It's not even stopping. Come on. All right. Let's go see. I gotta know what's going on with this thing. Oh, man. Oh, no.

Oh, man. So now having a master cylinder fluid leak like this, this is a very unsafe situation. This isn't something that you can just go ahead and drive wherever you need to go and then hopefully get around to fixing it at some point in time. This is something that as soon as you see that you have a brake fluid master cylinder leak like this, you need to make sure you call a tow truck, and then, of course, get it towed to someplace where you can physically work on it or have a professional work on it. For me personally, I'm gonna get this to the studio and we'll talk a little bit more about it.

Hey, friends, it's Len here from 1A Auto. So summer is in full swing. My buddy and I, we're getting ready to go out and do some kayaking while we had some free time together.

Hey, Len, where do you want it?

Just put it right in the back. Right there, pal.

Right here?

Yep. What happened when I was going out to go kayaking? Of course, I was going up a lot of hills. And down some hills. It's a cute, little trail. It felt like the brakes got a little squishy on me and at times, it almost felt like the brakes didn't even wanna stop the truck. Come on, stop, stop, stop. This thing isn't stopping, dude. That's a very scary situation for me. I know that there's a couple of different things that can cause this but for this one, in particular, once I popped the hood, I could see exactly what was going on. The master cylinder has a leak.

What is a master cylinder and how do I know that this is one of the issues that's causing my braking issue? The master cylinder itself is, of course, supposed to be able to hold all of your brake fluid up along the top here. It's kinda like a little reservoir for it. So essentially, when I go ahead and I step on that brake pedal, it's gonna force the piston inside this area right here where there's a couple of plungers and it's gonna draw some fluid from inside that reservoir, and then force it down the brake lines all the way down to my actual brakes.

Now how do I know that my master cylinder's bad? Of course, because I could find that I had brake fluid coming out of it right along this seal right here. Other than that, paying attention to it, I can see that my brake booster right along this area right here has a lot of paint that's missing from it. Why would it have paint missing from it? Well, brake fluid itself is corrosive and it's gonna go ahead and it's gonna try to eat off the paint from the metal. It's gonna swell it up and then it's gonna kinda come off of there. Also, I can see that it's a little bit moist. Why would it be moist? The brake fluid's leaking from down along this area like I said. It comes down this way due to gravity and then it makes its way back to the booster area right here. Of course, at that point, it eats the paint like I said, and it could eventually drip down onto the ground, which could cause issues with the grounds, such as may be contamination of water and such.

Now looking at the master cylinder itself, it kinda looks as though the fluid's probably full. I tried to wipe it off but I really can't tell the level. I'm just gonna go ahead and open it up. Oh. Oh, yeah. That brake fluid's super low and as you can tell, it's very old. This truck right here is a 1996. The brake fluid might've been in there since the beginning and the master cylinder's probably original as well. This right here is exactly where the leak is down along this seal. As you can tell, it's very low. This isn't good. Something else that I wanna mention about possibly having a leak, you might not visually be able to see a leak like what I have on this one right here. Maybe the leak is actually right behind this area. Possibly.

You have a brake booster that looks like this one right here and, of course, like I said before, the paint is just kinda coming off down along this lower area. Why would the paint be coming off? Once again, because of brake fluid. On the inner portion of this master cylinder, on the far side where it connects onto the brake booster, there's gonna be another seal. If that seal's leaking, there's a possibility fluid's leaking out. It could potentially come along the outside here or even on the inside of the booster. The only way we're gonna be able to tell if we need a booster or not is, of course, to remove the master cylinder and then inspect the inside. If there is brake fluid, you need to either service the booster or replace it as well.

At this point, we know for sure that we need a master cylinder, but we need to continue diagnosing. There's other things that are gonna be involved. Of course, there's gonna be lines that go onto the master cylinder. You wanna make sure that those are in good condition. If they're rusted and rotted and you try loosening up those fittings, you could potentially twist or even damage your lines causing a restriction or even another leak. Also, you wanna make sure that you double-check all of your brake lines that lead down to the flex hoses and, of course, to the brakes themselves. If those brake lines are rotted like I said before, you're gonna have an issue. The flex hoses themselves, if it looks like the areas where there's brackets are swollen, it could potentially be causing a restriction on the flex hose, which is gonna restrict fluid making its way down to the brakes. In which case, you're probably gonna feel like you have a braking issue as well.

Also, you wanna make sure that you pay special attention to the bleeder screws that are on the brakes themselves. In the front of most passenger vehicles, you're gonna have calipers. On those calipers, they're gonna have bleeder screws. Also in the rear, you might have calipers or you might have drum brakes. Either way, they need to have little bleeder screws on them. You need to make sure that they open up. If they don't, you might have an issue where you can't remove the bleeder screw, in which case, you're not gonna be able to get all the air out of the system after you're done doing the master cylinder. So, there's other things we wanna pay attention to before we start tearing this apart.

All right. So, I've got the wheel off of here so we can take a quick inspection. I'm looking at the brake pad. That doesn't look too bad at all. I think it's reusable. The caliper itself, we can try to push it back and make sure that it functions, but what I'm noticing on this one and on the other one, to be honest with you, is that the bleeder screws are completely rotted off. That's never gonna come out. Now, are these bleeder screws something that you would just wanna go ahead and condemn the caliper for? No. If you wanted to work hard, you could potentially get those out of there but, of course, you're gonna have to replace them in the long run. Putting those back in, it's gonna be useless.

You do have to remove them though because if we're gonna be doing the master cylinder, we're gonna have to bleed all the air out of the brakes. That means you have to check all four wheels, make sure that the bleeder screws don't look like this. For me personally, these calipers are kinda old. Maybe they work fine, maybe they don't. But what I wanna do is just go ahead and replace them. I don't need to go ahead and spend a whole bunch of time just trying to replace this bleeder screw. But like I said, it is your prerogative. If you don't wanna buy brand new calipers, don't. Just go ahead and work at it and you should be able to get out that bleeder screw.

Now once I've checked everything out and I know exactly what I'm gonna need to be able to fully do this job, I'm gonna go ahead and get started on replacing that master cylinder.

All right. Now that we have the master cylinder off of here, let's have a look at the backside. What you wanna pay attention to is see if you have fluid coming out of this area right here. That's the area that I told you if it was leaking, it could potentially damage your brake booster. We're also gonna take a look at the brake booster itself. Looking at it, I can see that a lot of this paint is starting to come off of it. I'm not worried about paint. It's more of a cosmetic thing for me. What I am worried about is just making sure that no fluid made its way into this drum right here. As you can tell on my particular application, it's nice and sealed up. I don't think any fluid made its way inside here. So I'll just go ahead and clean up all this paint mess right here, and then we can continue.

Now with the master cylinder out of the truck, I wanted to kinda start to take it apart so we can have a look at what's going on. But before we take it apart, let's just reiterate where it can leak. Along this seal right here is where we had our leak on this particular application. There's supposed to be a seal that's in between the reservoir and the actual cylinder area of it itself. There's gonna be one there and one right here. Another common area for these to leak would be this area right here. This is the part that went into the brake booster. I already talked to you all about this, but if the fluid was leaking down along this and it made its way into your brake booster, you're gonna have major braking problems and it's gonna be an expensive fix overall.

Now other than that, when I was cleaning this out, I happened to look inside the reservoir and this truck right here is a 1996, and I think that this master cylinder's probably original. The brake fluid that was in it, probably original as well. Before we start taking this apart, let's just have a look at the master cylinder. You're gonna see that you have the larger area of the reservoir right here. This is gonna be for your front brakes, and that's where the majority of the braking of the vehicle is gonna come from. The smaller side right here is for the rear brakes. That's more for stability. If you just had front brakes with no rear brakes, you're still gonna be able to stop. It just might not be very safe.

Why do they have two separate areas like this? Well, just in case you have an issue like what we had on this particular master cylinder. We had this area leaking right there. If I lost all the brake fluid inside this right here, as you can tell, I'm still gonna have plenty of braking coming from my front. Safety is in mind. That's why they designed it like this. Now let's start tearing it apart.

Get that out of there. Wow. That seal is extremely messed up. Grab this grommet out of here as well. Okay. So now we have a look at the areas where the ports were going into the master cylinder itself from the reservoir. Now if you had a clog inside this area here because your fluid was extremely contaminated like ours was with any debris inside there, you might potentially have an issue. Of course, the more that things start to leak and brake fluid starts to get up on this, it's gonna start to swell it up and that's pretty much what causes the actual leak. If it leaked a little bit, it's gonna continue leaking more and more as the seal got worse.

So now that we have that apart, we know that this was the area for the rear brakes, and then over here was for the front brakes. You can tell that there's definitely a difference on these ports and like I said, looking at the hole where the fluid's supposed to go into, if there was debris in there, that's gonna be an issue. Now I'm gonna get this in the vice. I'm gonna try pressing this in while I remove the little clamp that's holding it in. Now, this is gonna be under spring pressure. It's gonna be trying to force it out. So, of course, I wanna be very careful while I do this.

...the rest of this clamp out of here. Okay. Let's start taking this out of here carefully. All right. So now right along this area right here, you can see that you have a seal. If you had a fluid leak that was coming out the backside here towards where your brake booster is, this would be seal that's the issue. Let's keep drawing this out. Now, this next seal right here is the compression seal that goes to the rear brakes. Let's go ahead and pull this right out. Now, this is all underneath spring tension right here. So as you're pressing on the brake, it's gonna squeeze this spring in and that's what's gonna force the fluid from in this area to your front brakes and in this area to your rear brakes. And the spring right here would be what pushes everything back when you release the brake pedal.

So, we're gonna have a quick look at these seals right up along here. You can tell this one right here. It looks like it's a little swollen. Looks like it's getting ready to start rolling over. Those could potentially damage something and, of course, we might have a brake issue from that. Also, I wanna look at this shaft area right here. The fluid that was in this, like I said, is very old fluid. And definitely contaminated by the look of it. Let's go ahead and try to wipe it off and see what we can see. Oh, wow. Yeah. That's nasty. We definitely had some contaminated fluid in this. That could potentially cause an issue. If you have contaminated fluid, that could swell up the seals on this, which might be another reason why we had the leak in the first place.

Okay. So let's wrap this up real quick. We went ahead and we took apart our master cylinder because I wanted to see exactly what's going on inside here. I've never really looked inside and now I know. We have the plunger area here that, of course, has some seals on it. If either of these seals were bad, you're gonna have a braking issue. We have the ports that come up along this area of the master cylinder itself. If those are clogged up, once again, braking issue. Also, we had the seals that were up on this area here, which, of course, went in between the reservoir and the cylinder itself. What happens is, of course, they can get swollen due to contaminated fluid or anything the like. When that happens, of course, they're gonna start leaking over time. That's just what happens.

Now if you wanted to, of course, you could probably get a rebuilt kit for this. If you're handy enough and you wanted to try to rebuild it yourself, that's something that you could do. For me personally, I would just go ahead and replace it with a new one. They do have a core charge on these typically, so what that means essentially is they're just gonna wanna take this back. They're gonna tear it all apart, clean everything up, figure out what they wanna reuse, and then, of course, they'll replace the new parts as needed. More than likely, they're gonna replace all the seals. They're gonna clean this up. And more than likely, they might also reuse this after they cleaned it up. They would just inspect it. Of course, that's not really my job so I can't tell you exactly what they're gonna do. But for me personally, I'm gonna replace the master cylinder with a new one and I'll send this one back.

Okay, friends, I'm super excited. I got master cylinder in here. I'm almost ready to get out on my kayaking adventure with my buddy. The last thing that I have to do now is to go ahead and bleed out my system. What I mean by that is I wanna make sure that I get all the air out of my braking system. So, I'm gonna go buy my specific manufacturer bleeding sequence for this. Once I've done that, I'm gonna take it for a road test. And then, of course, we've already got the kayaks in here, so I'll probably just grab my buddy and down the river we go. So, I'm gonna go ahead and get to it. I hope you like the video. I hope you learned a little something. If this video helped you out and you wanna share it, please feel free. If you liked the video, smash on the like button for me. It would mean the world. While you're at it, go ahead and subscribe and ring the bell and that way you and all of your friends can be kept up with all of our latest content. Thanks.

All right. We made it. Finally. Let's start unloading these kayaks. Sounds like the water's rushing down there. Let me check it out first. I don't know about this, bud. Oh, boy. I don't know. What do you think? Might be a little hairy? Could be an adventure. What do you think?

Man: Yeah, let's do it.


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