Ever Wanted to see the inside of your brake booster?

[Legacy777]

I've been meaning to do this for a while, and finally got around to it. The booster wasn't too bad to take apart. It had bent in metal tabs on the outer shell that kept everything together. I just flatened them, and started taking apart the booster.

Here's the pics. I have labeled things, so hopefully it'll help in knowing what is what

http://www.main.experiencetherave.com:8 ... kebooster/

Here are scans that show the booster's coponents and its operation.

http://www.main.experiencetherave.com:8 ... oster1.jpg
http://www.main.experiencetherave.com:8 ... oster2.jpg
http://www.main.experiencetherave.com:8 ... oster3.jpg
http://www.main.experiencetherave.com:8 ... oster4.jpg


Now here's a couple things I learned from this whole process. The claim about a "dual stage" booster is complete and utter rubbish. Both diaphragms are fixed to the same plastic body and move as one unit. The poor pedal feedback and/or "dead pedal feel" at the top of the stroke is caused by having too much vacuum assist, and or the design of the booster. The single diaphragm booster eliminates the "dead pedal feel" and provides much better pedal feel.

There is slop in the booster setup, i.e. the operating rod does travel about an 1/8" before actually coming in contact with the reaction disc, which by the way is made out of rubber. I believe this is done though because the poppet valve seals off the passages between the diaphragm & atmospheric chambers when the operating rod is depressed slightly.

If you take a look at the scans and the pictures I took it will hopefully make more sense. I don't claim to 100% understand exactly how the valve body is setup, but I think I have a good grasp at how everything is supposed to work.

[Subaru_Nation555]

Very interesting. I have been wondering how a brake cylinder works but haven't really researched it. Good post.

[Legacy777]

this is the booster only....not the master cylinder.

[Legacy777]

Update

I've looked over the booster a little more closely, and have identified the passageways and for the most part understand how it works. With vacuum hooked up and the pedal not depressed, there is vacuum in both sides of the diaphragm plate. The poppet valve seals the valve body and doesn't let vacuum escape. When you first depress the brake pedal, the poppet valve retainer/washer, comes in contact with the stops. When this happens the poppet valve seals off the vacuum valve passage. When this occurs passages A & B become isolated from each other. Also, when the poppet valve retainer/washer hits the stops, it allows the vacuum to escape through the center portion of the shaft. You can see what I mean in this pic http://www.main.experiencetherave.com:8 ... P_3761.JPG

The only thing I haven't fully come to grips with is how the plunger valve seals itself between the vacuum and atmospheric side. There's no rubber seal, so in this pic, http://www.main.experiencetherave.com:8 ... P_3757.JPG vacuum can pass through the center hole to the atmospheric side. I had thought that the plunger valve gets sealed on the reaction disc since it's rubber, however I don't think that's the case because the plunger valve extends further forward then the surrounding valve body.

Here's some more pics
http://www.main.experiencetherave.com:8 ... kebooster2

I wish there was a way to test out air flow through some of the passages. It might help in understanding things more.

As for modifying the booster to reduce assist. I don't really see a way. As Duncan mentioned, reducing the spacing between the plunger valve and reaction disc might eliminate some, but for most people that's not really an option. Best solution....get the single diaphragm booster.

This scan has more detail.
http://www.main.experiencetherave.com:8 ... ooster.jpg