bypassing brake proportioning valve

[Guest Anonymous]

I have a 260z with the brake proportioning valve. It is either not working correctly or barely lets the rear brakes do their job. I've noticed early z's do not have this valve. Is their a short line available to bypass this valve?

 

Brian

[Dragonfly]

Don't bypass the valve it will cause you problems. The early Z's do have the valve also but instead of being on the fire wall it is in the back of the car just forward of the fuel tank.

 

Since you dont seem to mind opening the brake system go ahead and pull the proportioning valve and take it apart, you will be blown away by the amount of gunk and crud built up in it. Clean it up and put it back together and do the same thing with the brake light switch (the valve with the wire going into the top). You will find it makes a world of differance.

 

P.S. while you are at it flush that 20+ year old fluid out and replace it, you should flush your brake system about every two years plus or minus depending on your driving and the general environment you drive in.

 

Dragonfly

[Guest Anonymous]

Thanks!!

 

Brian

[zcarnut]

If you are just wanting to temporarily bypass the proportioning valve on your 260Z, then I would recommend removing the valve. Unscrew the large nuts on the ends of the valve and remove the aluminum valve plunger and reassemble the valve. Replace on the car and go for a test drive. If the internal valve is stuck or the insides of the proportioning valve are corroded (very common) then the proportioning valve needs to be replaced. They are not re-buildable. New ones are probably over $200, so I would hit the junk yards and hope you can find a good one. This is just another reason to routinely flush your brake system with new fluid.

 

Nissan used the same the proportioning valve on the 280Z’s. Just remember to use the coupe valve if you have a 2-seater and the 4-seater valve if your 260Z is a 2+2. They are different internally. Like wise, the 280ZX valve (and the 810/Maxima one) is identical externally to the 260Z/280Z but it has a different valving characteristic.

 

BTW, the 240Z’s had a proportioning valve as well. It is located nearer the rear brakes on the tranny tunnel and also serves as the brake line splitter for the rear brakes. However, the 240Z is the more standard “two-way” proportioning valve whereas the later Z car valves also have an interface to the front brake lines (“four-way” valve).

[74_5.0L_Z]

Brian,

 

As a fellow autocrosser, and as a owner of a 5.0L powered Z, here is my solution.

 

First, I removed the stock proportioning valve. I simply unbolted the lines from the valve, removed the valve and reconnected the lines with brake line couplers.

 

Second, I installed a Wilwood adjustable proportioning valve in the line going to the rear brakes. This can be placed so that the adjusting knob is in the cockpit, or the engine bay.

 

Third, I drove the car and adjusted the bias to get all four wheels to lock simultaneously. Be sure that the rears do not lock first. The car will instantly swap ends.

 

I have Mike Gibson's stage II breaks on the front(11.75"), and 10.75" vented disks on the back. The front calipers are Outlaw with (4)1.75" pistons, the rear are Outlaw with (4) 1.375" pistons.

 

With this set-up, the proportioning vale is adjusted ~ 75% of its limit to prevent the rear tires from locking first.

 

P.S I outbrake everyone at my local autocross.

[Guest gprix1]

74_5.0L_Z,

Your solution was exactly what I had in mind. I'm glad someone has validated it with actual application. I imagine you want to have the rears nearly closed to start with and open it slowly 'till you find the correct balance; correct?

 

- Rick