What's the reasoning for the 3 brake lines on the master cylinder, and what's the purpose of the wires coming out of the master cylinder reservoir, or however it's spelled?

 

wires are for low fluid level I beleive. 3 lines are two for front and one for rear. someone can correct me if I am wrong as I am running different setup now.

 

If the wires are for low fluid level, how can it possible know, there's no physical connection to the liquid in the reservoir!

 

 

^^^Yeah, that.
The float that's in the reservoir gets sensed by the,... sensor.

 

Magnet,... metal reed switch,... continuity = brake fluid level.

 

Another question, why did they need 2 brake lines for the front when most other vehicles only have 2 lines, one for front and one for the rear?

 

I'm no brake expert but everything since the 90's has anti-lock brakes, and several components between the master and the wheel brakes. My 2015 WRX and '17 FXT had crazy-looking anti-lock spaghetti-bowls.
Our cars are running basic brake technology from the '70's. One line to each front, and a line to the rear axle, meant that if any single hard or soft line ruptured you still had positive pressure to the other lines/wheels. You had several pumps on the pedal before you squirted all the fluid out, so you could safely stop the car after you noticed the pedal felt funny.
This was about the extent of affordable (non luxury car) braking in 1979 Japanese imports. All 1st gen RX-7's are like this. It beats cars from the '50's and 60's with only a single curcuit out to a splitter block. Lose any rubber line and you lost braking to all 4 wheels.
The corvette had 4 wheel independent suspension since '63 and 4 wheel discs since '65, but Mazda was trying to sell a new design with a revolutionary engine, so they went "basic" on the chassis. And for the price it worked very well, and almost any American mechanic could work on it. Because it was 60-70's technology in a sleek '80's body.

 

It also depends on whether the car is running a proportioning valve or not. If so you’ll usually see 2 lines coming front the master cylinder to the proportioning valve (1 front and 1 rear) and then from the valve you’ll have the lines that split out the the brakes themselves, typically one to each front and a single running to the rear. If the car is running drum rear brakes one is enough but with disc rears you may see two. Since most braking power is portioned to the front brakes and they run larger size calipers they need more volume of brake fluid, hence more lines to carry that extra volume.

 

Our cars are a little strange (to me) in that the LF line is direct from the MC, but the RF and Rear go through the stock prop. valve.

 

Does anyone out there know how a person could hook up a line lock to the front brakes, with that 3 line system out of the master cylinder? Any help will be much appreciated. Thanks!

 

There are several threads about line-locks and I'm not sure what the best solution is, but here's a pretty good reply from @peejay in 2002 -

From peejay -
"The problem is, the front brake lines are separate all the way to the master cylinder.

That means, you either need two line locks, or you need to plug one of the front brake outlets on the master cylinder, run the other line to the line lock, then run a T from the line lock to send the fluid to both brakes.

If that's not tricky enough, you have to do this AFTER the proportioning valve. Fortunately, only one of the front brake lines goes to the proportioning valve, so your work is at least clear-cut now - you need to put the line lock in the right brake line downstream of the prop valve, then run a T after the line lock to the left brake, and plug off the master cylinder where the left brake used to get its feed.


NOTE - I have not done this yet - I am perfectly happy with three pedaling my burnouts (no "stomp the brake AFTER starting the burnout" for me - that just looks so cheesy IMO) but this is a subject I've given a long hard look to, and probably will do someday. "

That thread - https://www.rx7club.com/1st-generati...-i-need-99134/