Brake Master Cylinder, booster, or proportioning valve?

You need to use Techstream to bleed Prius brakes. They are not normal.

Brad

 

Since you have a Gen 1, you might find it at the edge of possible to bleed the master cylinder/actuator/accumulator without Techstream, by studying the electrical wiring diagram, and the hydraulic diagrams in the New Car Features Manual, together. Or you could go the Mini-VCI route as so many do.

The pedal-slowly-going-down-when-stood-on certainly suggests an internal leak (if your reservoir level stays put and you see no fluid on the ground). You're also in luck in that the Gen 1 seems to be the last Prius model for which you can buy the master cylinder rebuild rubber kit, not just a whole new MC.

You can get all the part numbers from most of the online Toyota dealers now. I can remember when a lot of them would let you search and buy parts but hide the part number, but that's much rarer now. I often go to Village Toyota just because they were early to see the light and now it's a habit with me.

-Chap

 

It's pretty much the first thing covered in the factory manual brake chapter.

 

I bleed mine after I did the actuator by bringing it on a dirt road and activateing the abs over and over

 

The guys that were supposed to send me a brake booster pump, sent me a low mile master cylinder by mistake.. Very clean, looks like new. Thinking I may keep it. It's probably worth more than the $90 shipped that I paid for it.

The booster pump that I got at the local Pick n Pull isn't quite as pretty, but it's functional and only set me back $30. It's in the car, btw, but still needs some connectin' and bleeding. 95* here today, tomorrow cooler. I expect I'll finish it.

 

I'm bleeding mine, in the middle of the process. It's a pretty much physical process--bleeds just like any car. If you have the warning buzzer and codes set, you need techstream to clear them. You use the 'clear codes' utility--unplugging the 12v won't clear them.

Chap, you seem to differentiate between Techstream and Mini VCI, could you explain?

I looked for the lowest mileage booster pump on Ebay. Found one in the local Pull a Part for $25, I don't know the mileage, but it bench tested as good (motor worked) and the one I pulled out had a dead motor. We're using a time tested car, why not time tested parts as well?

 

Well, the distinction is Techstream is Toyota's software for working with the car, it runs on a computer, and you need to connect the computer to a J2534 adapter to plug into the car. Mini VCI is one of those, but not the only one. It gets discussed sort of interchangeably with Techstream because many of the vendors selling cloned Mini VCIs (the only kind you can get; the cloning drove the original maker out of the business) include cloned Techstream with them.

As for bleeding the brakes, if you study the hydraulic diagram, there is (if I recall correctly) one hydraulic passage within the actuator that you cannot bleed without energizing one of the solenoid valves controlling it. If air has entered the actuator, that's what the bleed procedure in Techstream will do, it commands the brake computer to open that valve.

With the Gen 1 actuator so (compared to later gens) simple, it seems if you really had to, you could complete a Gen 1 bleed by studying the hydraulic and wiring diagrams, and identifying the right pin to supply voltage to in order to open that valve. I've never tried it or heard of anyone else doing so, and you would want to know how long the valve can safely be energized without overheating, or maybe tickle it not with 12 volts but with the lowest voltage that makes it barely open.

The hydraulic pathways and number of valves in the Gen 2 actuator got so complex by comparison that there is probably no sane way to bleed that actuator other than using Techstream and telling it to go through the procedure. But in Gen 1 it might be possible if necessary.

-Chap

 

Thank Chap. I used techstream (the one that came with my Mini VCI cable) but couldn't see a utility to engergize the SRRR solenoid. Factory instructions say to use a "Toyota handheld scanner" to activate the solenoid. I guess bleeding the brakes is a 'do it the best you can' effort. Brakes are bled, using a vacuum bleeder. They seem to be acceptable. The alternative is to take it to a Prius shop and PAY to have the brakes bled--a prospect that is unpalatable at best!

 

I was wondering where the brake cylinder even in in my car. ( 2007) I would like to service the brake system my self as I am a student but I have to figure it out on my own otherwise I an not leaning. so I came here to ask questions......Any takers?

 

For your 2007, you would want to be posting in the Gen 2 forum (this discussion here is for Gen 1, 2001 to 2003).

The diagrams in the 2004 New Car Features manual (more info) should answer a lot of your questions.