Diagonal Braking Systems

[stradlater]

I found out some months ago that the ra23 celica (and probably many others) has a 'diagonal' braking system.

I believe this means that if the front right brake fails, the rear left fails, rather than both the fronts. something about keeping balance.

Anyhow.

I installed my line locker simply at the first point in the 'front' brake lines. straight out of the master cylinder. This has caused no end of grief to my braking balance, force required, etc..

I believe it's because I haven't installed the line locker correctly.

Now, I know the simple answer is "install the line locker correctly" and I have the documentation to do that, but does anyone now how to 'un-diagonalize' my braking system? I don't see any particular bits in it that make it specifically diagonal, but I think I'm missing the point somewhere along the line.

Is anyone familiar with such things?

[PlacentaJuan]

so if one brake fails, another fails in sympathy? to keep it balanced?

doesnt make sense to me, how would the braking system know if a brake failed dues to pad failure, wheel failure etc?

i assume this system would only work if a brake line actually broke and lost pressure?

even then it would go 'diagonal' just so you could come to a stop and get towed home, its not for continued driving is it?

soudns wierd to me i would want to confirm this, however if such a diagonal system was realy then i would assume it is done in the master cylinder. maybe you can replace that to 'un-diagonalise' it.

[stradlater]

It is definately a diagonal system.

The failure I was referring to was if there was pressure lost. Something about Bias too I think more than anything else.

[stradlater]

I know this out take refers to FWD cars, but I think it's not quite hitting the mark. I know that my car has this setup, and this paragraph below is why:

On front-wheel drive (FWD) cars, the brake system is usually split diagonally. The left front and right rear brakes share one circuit, while the right front and left rear brakes share the other. This arrangement is necessary because the front brakes do about 80- to 90 percent of the braking, and FWD cars typically have a higher proportion of their weight over the front wheels, plus the front wheels do the driving. If a FWD brake system were split front-to-rear and the front brakes failed, the rear brakes alone might not be able to stop the car.

[RA35GT]

Hey man, I just went outside and checked my '35.
Front outlet on m/c come out and go to a t-piece, one side to left front the other to right front (i.e. fronts share a circuit, leak in left would result in no brake from right)
Rear m/c outlet goes down to some block thing (id imagine its either the pressure limiter or residual pressure valve or both) after this it goes to a single line to rear of car. Which I'd imagine is then teed at the axle. for left and right.

If your car is indeed diagonal, you can undiagonalise it by running new brake lines, you may need to review brake master cylinder sizes and/or piston sizes though.

[The Real Roadrunner]

early celicas dont run a diagonal system its mainly just euro stuff that runs them.

it should be a descibed above with a t for the front pair and a single line to the rear with a splitter on the diff housing. there may be a bias valve on them that someone has stuffed up refitting the lines to.

cheers
linden

[oldcorollas]

yah, volvos and such do... it is like an "extra safety" item... didn't they also run sperate circuits within the frot calipers? i forget
as linden said, look for the single line running to the rear.. must be twin line if it is diagonal system..

[lexsmaz]

Definately would not have a diagonal braking system, & fwd that have that system are also coupled with a steering geometry that has a positive scrub radius .. so if you lose a circuit in the brakes & jump on the brakes the front wheel that is left operating tends to steer inwards slightly under braking .. ( Makes the car more stable ) ...

[stradlater]

Ok, twin lines to the back makes sense..

But why then does installing a line locker cause the whole thing to be thrown out brake bias wise?

[PlacentaJuan]

mabye you have the locker the wrong way around?

that is interesting about the diagonal system, i understand it now.

[RA35GT]

yah, volvos and such do... it is like an "extra safety" item... didn't they also run sperate circuits within the frot calipers? i forget
as linden said, look for the single line running to the rear.. must be twin line if it is diagonal system..

Yeah volvos has two separate lines to each caliper, so if one ciruit failed, half the caliper would still work.

stradlater: Is the line locker installed correctly now? How is the bias thrown out? (I assume too much rear?) Is the solenoid faulty and blocking the front brake line without being energised? I assume the brakes have been rebled?

[stradlater]

brakes have been rebled more times than I care to mention.

It has thrown the bias out to too much rear, yes.

Not sure about the blocking the fronts thing though.

Not entirely sure how to check that one.

[allencr]

Stick your head under a Volvo next time you've got a chance, and you'll see LOTS of extra plumbing, and it will will look nothing at all like what you've got with a single line going to each wheel.

You're doing something wrong or the part is bad.

[The Real Roadrunner]

can you throw up a diagram of what you have done / where all parts are fitted?

also, why did you fit it to the front line? ive found best results come from fitting them in the rear line and closing the valve to the rear therefore you still have control over what the front of the car does during a burnout.

cheers
linden

[stradlater]

The way I figured it, I couldn't see how it would work on the rear longs. It's for holding pressure ON not holding pressure OFF..

I'll put up a diagram later on, but basically, what used to be

Master Cylinder <--------------------------> Distribution Block

is now

Master Cylinder <------>Line Locker Solenoid<-----------> Distribution Block.

Nothing more complex than that. Other than to say the line locker sits above the brake fluid reservoir, so maybe that's a problem, but I can't see how.