GSGALLANT

Hey everybody,

I have a 2002 4Runner with a hydraulic brake booster & ABS. I have searched the forum, as well as the FSM and a Toyota Brakes manual that I have, but have not been able to find an answer to my question.

Does anybody have (or know where to find) a detailed instructions manual describing how my braking system works, complete with fluid flowpath diagrams, and schematics showing the inner workings of the master cylinder?

I have found this: Rav4 Braking System which describes the braking system on the Rav 4. Does anybody know if my 4Runner system is similar (except without the regenerative braking feature, as best as I can tell from the FSM)? I know the systems won't be identical, but I'm looking specifically for the inner workings of my master cylinder... is it similar to the one in the Rav4 document? (See page number 42 of the document... [which is page 9 of 24 in the PDF])

Thanks,

marko3xl3

This is how ours work (plain jane):

http://auto.howstuffworks.com/master-brake.htm

On that site, search for "brake" and you'll find many many other VERY GOOD brake related info.

MTL_4runner

This is about as good as you'll find online.....check in the FSM if you need more:


Is there a specific problem you are trying to diagnose?

eric-the-red

You guys haven't seen a brake master from the 01/02 Runners. It looks like something from the space shuttle. No more vacuum booster, it's electric, with a metal cylinder attached that warns 'Nitrogen Gas Under Pressure'. It's got about 5-6 electrical connections. I'm almost too scared to attach my Motive bleeder to replace the fluid. I keep having nightmares about the bleeder taking off into orbit around the garage lights.

GSGallant, the only thing I've found is a wiring diagram, nothing about the hydraulic workings. The one from that RAV seems to have a lot of the same parts as mine, though there might be some extras on the 4Runners because of the Stability Control.

GSGALLANT

Yeah, Eric-the-red... you're bang on about the space shuttle comment. As best as I can tell, it's probably very similar to the Rav4 system, but I don't want to assume that it's exactly the same. The metal cylinder is a dual section accumulator tank. The booster pump takes brake fluid from the reservoir, and pumps it through a check valve into the accumulator, compressing the nitrogen (through a diaphragm, I assume) which stores the brake fluid under pressure. This fluid under pressure, goes to... (those three dots are the part that I want to confirm.)

MTL 4Runner, as an answer to your question "Is there a specific problem I'm trying to diagnose", I'm soon going to be flushing my brake system, and I just like to know what I'm getting into before I start. For example, there are some posts here (that the question has not been resolved yet) about people trying to bleed the brakes on a 01/02 4Runner with a hydraulic brake booster.

They say that with the truck off, you can't bleed the rear brakes with the brake pedal method. In the section to check the operation of the brake booster in my FSM, it has you apply a certain force to the brake pedal with the truck off, while measuring the pressures at the front and rear brakes. The result you're looking for is 0 psi at the rear, which explains why you can't bleed the rears with the truck off.

The above Rav4 system explains that exactly, in that the hydraulic booster supplies direct pressure to the rear brake system when the brake pedal is pressed down (it opens a port that connects the booster to the rear loop). This back pressure in the rear loop becomes reaction pressure which in turn allows the front loop to become pressurized.

Without pressure in the hydraulic booster, that back pressure is not present, so you effectively have no rear brakes if your booster fails. You only have manual brakes in the front loop.

MTL_4runner

You might try using a motive power bleeder instead to bleed but it may be complicated since the fluid routing is different than other years.
If the bleeding procedure was significantly more difficult, I might question the benefit gained (vs potential air in the system).

BTW, GSGALLANT, where in NB are you?

GSGALLANT

The bleeding procedure is the same as for any other vehicle, as long as the ignition is selected to "ON" (the truck does not have to be running, though.) I'd like to get a motive power bleeder... I may still order one...

By the way... I'm in Saint John, NB, MTL_4runner.

surf4runner

which is a good reason to keep the back brakes properly adjusted. parking brake=emergency brake