Question for those who have had bad brake booster

When the clicking is happening how hard are you on the brakes are you actually using the hydraulics That's pretty smartly pressed down? That's usually where most people are on the brake. To be all the way down in the hydraulics where you're actually squeezing the calipers onto the pads n rotors. Is kinda newbie move I guess I'd call it.

 

My booster assembly already had one foot in the grave at the time I bought the car, but I do not remember a clicking noise in the 2 years I put up with the issue.

Can you perhaps have someone help you in figuring out the source of the clicks? Is it from within the cabin or the engine bay? Driver's side or passenger's? From the fuse box, the brake master cylinder assembly, or somewhere else? Do the clicks continue as long as you hear the booster pump run, or are they before or after?

 

Sometimes if there's a leak in one of the pressure-reducing valves, there may be a fluid pressure reading that keeps slowly decreasing as you sit there holding the brake. The ECU will see the pressure slowly decrease, and repeatedly click a pressure-apply valve, to poke the pressure back up. If you are graphing that pressure with a scan tool, you may see something like a sawtooth, jumping up with each click you hear, then slowly sinking again.

The fluid valves in there make more of a muffled sound that I might call more of a thunk than a click, but aside from what we call the sound, this is one possible story for what you're seeing. If you were to post a recording of the sound, it might be easier to judge whether it's the right story.

 

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I'm not sure I made a positive ID of the clicking sound on its own, but toward the end of the clip I also heard your pressure pump run.

If you happened to mash the pedal harder just at that moment, that might have started the pump. But otherwise, if you were really just holding the pedal steady that whole time, the pump running tends to confirm what the clicks were. As the system kept valving more fluid into the circuit to make up for the loss of pressure, eventually the pump had to run to make that back up.

While it's theoretically possible that an external leak—fluid leaving the car—could be the culprit, have you noticed any spots of brake fluid beneath the car, or on the undercarriage?

Much as I hate to bear bad tidings, usually the cause is an internal leak: one of the valves internal to the actuator isn't sealing perfectly, and the fluid just finds its way back to the reservoir. None actually leaves the car. Solution is replacing the actuator.

Note: if you want to investigate the external-leak possibility, do not just get up close to rusty brake lines to watch them while a friend mashes the pedal. Use cameras, mirrors, paper towels, or something. I have seen lines split so subtly that they don't leak a drop until the pressure inside gets up toward 2000 psi, and then suddenly squirt a jet that could inject through skin. Unlike the nifty injections on Star Trek, real-life fluid injections can cause serious injury sometimes requiring amputation.​

 

There are these two assemblies under the hood:



The one on top goes by all of these names:

• brake booster
• brake master cylinder
• brake actuator
• skid control ECU

The one on the bottom goes by these names:

• brake booster pump
• accumulator

You're not the first person to find the names confusing. Just look how similar the names "brake booster" (the top thing) and "brake booster pump" (the bottom thing) are. Or "actuator" (top thing again) and "accumulator" (bottom thing again).

The top thing's the one with nearly all the valves in it, and the thing you hear clicking to maintain the slipping pressure.

The bottom thing is what you hear pumping at the very end of your clip to restore the fluid pressure the top thing has been using.

Your problem is probably in the top thing. (Which is good news, because replacing the bottom thing is a knucklebuster job.)

On the other hand, the bottom thing has probably been running extra often because of the problem. If things have been like that for a while, there could be some extra wear on the bottom thing too.

 

Because the top thing has so many little valves in it, it's the one that is kind of a failure magnet.

Pretty much the only ways the bottom thing can go bad is for its internal bellows to crack or the pump to wear out. Those things can happen, but they don't always.

As you clearly have a problem with the top thing, it would be reasonable to replace that. The bottom thing is a PITA to replace, but if that becomes necessary it can be done then. It doesn't have to be done at the same time as the top thing. Because some early units of the bottom thing needed to be recalled, Toyota came up with some clever tools and methods for sneaking it out and in with a minimum of disassembly around it.

 

Some info from Toyota:

 

Usually the latter—just the pump having more work to do.