Monthly Archives: July 2014

Brake Booster and the Locked Up Brakes

This blog is a little different. Usually I am talking about building something for the Magic Bus. This time, it’s about repairing. Normally I wouldn’t blog about this, because I repair all the time. This one is different though. This was something that was new for me and something I found to be new to a lot of people online. Many forums have people asking for the answer I am about to give, and instead of answering them all, they will hopefully find this. So if you changed your brake booster and your brakes are locked up, here is why. Unfortunately you are going to have to read my story first.

It all started when my brakes started getting a smooshy feeling. I first thought I needed to bleed the brakes. That is why I tried to get the right rear tire off. Well, it didn’t want to come off. I got all of the lug nuts off except for one. That one was rusted solid, fused to the rim, and now rounded over. I heated, I used rust removers, WD40, other lubricants, and a rounded head socket on an impact wrench. Nothing. Even after I grinded the nut practically in half, it still wouldn’t budge. So I ended up just grinding the whole thing off. I figured I would just replace the lug itself. That’s when I discovered that the drum was rusted on as well. Ugh!

While all that was going on, in the hot Texas sun, the brakes got worse and it was obvious that is wasn’t just some brakes than needed to be bled. No, this was much more. So I looked around and followed the mechanics of the brakes. I noticed something I had never seen before. A big cylinder box that was inline with the foot pedal and the master cylinder. After some research, I discovered this thing was called a “Brake Booster”.

Brake Booster

Basically, the rod continues from the pedal to the master cylinder through this thing. Connected to the rod, inside the cylinder, is a diaphragm. On one side of the diaphragm, the chamber is connected to the vacuum system of the engine. So when you push in on the pedal, it opens a valve to let air in on the opposite side, which allows the vacuum to pull in and help you push on the brakes. That is what it does, it boosts your foot pushing on the pedal so that it’s not as hard. If you want to know more, this will tell you, but you should get the jist.

I found that you can get the booster and master cylinder as a set for only ten more dollars than just the booster by itself. So I went with the combo. Might as well get a new master cylinder while I am at. So I pulled the old set right off there. Not a problem. The bolts were rusty, but they hadn’t fused. Nothing like that lug nut and drum that I was working on at the same time. Not to mention that I had checked other tires and found three more lug nuts that don’t want to come off.

Brake Booster

I had to bleed the master cylinder, so I put the two pieces on separately. I first put the booster on. Now I noticed that the rod on the new one was a little longer, but no big deal. I got it on there. I then hooked up the bleeding tubes to the master cylinder and got all the air bubbles out. I had never done that before, but it was quite simple. It took some effort to push the piston in, but it wasn’t that hard. I then put the master cylinder on. Not a problem at all. I even tested out the brakes a little. They were tight. You barely touch them and the brakes were activated. I drove back in forth in the driveway a little. Seemed fine, even though it felt like it would take some time getting used to.

Brake Booster

Time to take a drive and really test the new brakes out. I set off down the road, passed a stop light, got onto the highway, and then it happened. The Magic Bus started to slow down and it was getting hard to make it move. The brakes were locking up and I barely made the exit and to the excess road. I had read the link above and knew how the booster worked and I had a feeling the problem was that the rod was too long. I had pushed the rod in to get it to fit right, and that was opening the valve on the booster, which was activating the brakes. So I figured if I just slacked off the booster I can at least get it home. That is when I realized that I didn’t bring my tools. That meant that I had to walk back. I had to walk back midday in the hot Texas summer sun. It sucked.

After making the walk, drenching myself in water, and laying under a fan with the air conditioner turned down low, I grabbed another car and drove to the van with my tools. I loosened the bolts on the booster and just let the booster hang loose in there. It worked enough, enough to get home, but now I am one person with two vehicles. So yes, I did what you have thought about before, I leapfrogged them back home. I drove the van a little ways towards home and stopped. I then walked back to the other car and drove it a little farther past the van. Then I walked back to the van and drove it a little past the car. Then I did that all one more time and I made it home with both vehicles. I did it all in the hot Texas sun. It sucked!

I looked all around and there was nothing that could be adjusted on anything. There was no screw to turn, no nut to move, no different hole for things to go in, no anything. The only thing to do was to move the whole system back a little. The only way to do that is to shim it out. So I got some washers, and a stack of four did the trick. That bumped it out enough so that the valve wasn’t being opened on the brake booster. Because that was what is happening, and if you are reading this because you have the same problem, then you need to check to make sure the booster isn’t being pushed in. The difference between four washers, about three eighths of inch, was all it took to open that valve and activate the booster. And if there is no way to adjust it, just bump that sucker out. Works perfect now.

Brake Booster

Now back to the lug nuts and that brake drum. Well, I got the drum off and replaced the grinded down lug. I am currently still working on getting the three other rusted lug nuts off. I’m not grinding this time. Nope, just rust dissolving lubricant and an impact wrench every day until they come off. There it is ladies and gentlemen, the Magic Bus and me, Randi Rain. Pretty damn funny huh?