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It seams a few of us around here are having problems with our brakes so I thought I'd start a thread. My 74 260z is having some problems as well. I was reminded recently of dual diagonal brakes, and how they were comonly used in the late 70's.

This is a system that is designed so that if you loose say the rear right(passenger side) you can stop in a straight line still. It works like this...

0=good brakes
x=dead brakes

O-O
----- brake system is fully functional and in good working order
O-O

If

X-0
---- Front left brake failer! in a non-dual diagonal car
0-0

Then dual diagonals will act like this

X-0
---- or vice versa in a dual diagonal system.
0-X

This stops the car in a straight line

There have actually been problems reported of early 80's nissans having problems with this system. In fact you can actually see increased wear on these systems.
280zx is a car that definatley has this system on it.

I don't know for sure but first gens may have this as well. So if you watch you wear you can see if you are having a problem with this system. So if you see wear on the 0 and very little to none on X... A quick tip would be to keep you wheels clean and see how much brake dust acumulates on the wheel during a period.

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A common failer is caused by water!

Brake fluid is hydroscopic! that is it retains water. This water is feed by gravity to the lowest points aka wheel cylinders and calipers. It then rust stuff up and is not conducive to a hydrolic system and it's physics. in other words water will compress under pressure and will not give you as much force as brake fluid and or could cause you brakes to fade entirely.

the fix could be as easy as do a FULL bleed, or you my have to rebuild the calipers and wheel cylinders even though the brakes did work last week.
most of the time people describe this problem as the black or brown stuff ozzing out of my bleeder screw! Bleed the system clean 2 times for satisfaction. expect to use 2 quarts or so of dot3

This is probably the most common failer up against the next type of failer.

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The next failer is in either the master cylinder or the proportioning valve.
I personally have very little knowllege abotu the proportioning valve maybe someone else will fill in the blanks.

If you have a clean system! and your foot goes to the floor whilst a fountain of brake fluid spurts out on open cap you have a bad master cylinder! heres your sign...

couldn't help myself.

if you go to bleed your brakes and none of your four wheels is getting pressure or very little pressure then the rubber seals in the master cylinder have gone bad! It will still be possible for it to show pressure on the bench, but it is bad. As I said someone will have to fill in the blanks here for the proportioning valve..

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These are typical failers. There are others. Such as the one I just fixed. My rear right wheel cylinder blew up in the worst way! The seal literally exploded under pressure and flew past the piston and into the brakes. The brake fluid wasted my shoes!!!!!

I then realized I had 2 problems!

I lost almost all my braking power! This doesn't sound weird but it is since I still had consistant pressure at the floor. This leads me to thing that the 260 my have dual diagonals. Failing duals but duals. My front resivour or rear brake resivour almost went empty but just refused to let the last 1/4" out. If someone would shed light on this that would be great. This does explain why though that my cylinder went out. I understand that the pressure being forced into the cylinder blew it out, if I have duals that are failing. I need some light shed on the proportioning valve and a little on the master please.

Ray
 

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Well, first, ................

........I doubt that you have a Dual-Diagonal system on such an early model ZEE........You can verify this by simply checking the brake lines to the rear wheels..........If there is only ONE line through the center chassis supplying the rear, and then split off to each wheel, it is not DD.

Your reservoir didn't completely empty since you had sucked air into the master, and basically weren't pumping fluid with the piston, just compressing air.

Proportioning Valve
The proportioning valve equalizes braking action with front disc brakes and rear drum brakes. It is located in the brake line to the rear brakes. The function of the proportioning valve is to limit pressure to the rear brakes when high pressure is required to apply the front disc. This prevents rear wheel lockup and skidding during heavy brake applications.

An added safety feature found on more modern valves is the ability to "warn" the driver that the system has a leak or that either the front or rear is non-functional, possibly due to low fluid in the master.......this is shown to the driver as a red dash light "Brakes", and this circuit is closed by the switch shown in the valve below. (again, this feature not found on early ZEE's)






So, what happened to your cylinder to make it blow out??

Bad cylinder seals............Plain and Simple.......probably nothing at all to do with the rest of the system, with the (tongue-in-cheek) possibility of contamination (dirt, etc.) wearing the seals over time.


PeeEss........rebuilding cylinders is NOT a good idea.


PeePeeEss......Today's word is .........."Failure"


Enjoy.............
 

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Re: Braking problems: yeah you having them, and you who have the

The early cars don't have a diagonal braking system, there is only one brake line going to the back of the car. My guess is the master and/or the proportioning valve make be screwed up as well.

I don't think the ZX's had this diagonal setup either but not going to swear on that one. I do know the early cars didn't for sure.
 

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Re: Braking problems: yeah you having them, and you who have the

If you use DOT 5 brake fluid you will eliminate the water problem and if it gets spilled on any painted surface it just wipes off witout messing up the paint.
 
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