rear brake proportioning valve

[sweatybetty]

this is the valve (tee) above the rear end. for a 72 240

thanks all

[Zed Head]

The "T" and the proportioning valve aren't the same thing.  There's one of each back there.

[Patcon]

Are they different on each S30 or all the same part? I may have one close at hand if the 280Z is the same

[Walter Moore]

The 240Z "proportioning valve" is a hydraulic timer/delay mechanism. It doesn't proportion the pressure to the rear brakes, it just delays their action so that in a panic stop the front wheels lock first. (To prevent a spin.) It was used from 1970 to sometime around 1973. I believe that the 260Z and later cars had a true proportioning valve that is located in the engine compartment. The early valve is no longer available, or was when I last checked.

 

[Zed Head]

I think that he needs to distinguish between the "T" and the "valve".  He hasn't really said what he's looking for.

Seems like with all of the mods that we do and lowering and variety of brake pads out there that eliminating the factory valves altogether and replacing them with a true adjustable proportioning valve would be the way to go.  I changed my front pads to ceramic a few thousand miles ago and I'm sure that it affected the ratio, front to back.  The new pads don't have as much grab.  But the wheels do stay cleaner.  Probably eating up my rotors though.  Digression.

Edited April 3, 2016 by Zed Head

[EuroDat]

9 hours ago, Patcon said:

Are they different on each S30 or all the same part? I may have one close at hand if the 280Z is the same

Charles,

The 280Z uses a different style proportioning valve and is located in the engine bay. I think they changed it somewhere in mid to end 1972 on the 240Z.

 

[sweatybetty]

my car is an early 72. there is nothing there now, so i am not sure what i am missing. i did see 1 picture that called it a "proportioning valve" and 1 of the vendors sells a rebuild kit for it, but im not convinced its anything more than a tee.

[Zed Head]

I got the fragment of picture I posted from the 1972 Brake System chapter.  They call the "T" a 3-way connector.  Page BR-5.  Shows all of the stuff that's missing.

[jfa.series1]

Looking at the online parts catalog, the proportioning valve was in the rear thru 06/72 build dates and moved to the firewall 07/72 and later.  The early versions are called a proportioning valve (46400-E4100), are NLA as stated.

 

http://www.carpartsmanual.com/datsun/Z-1969-1978/brake/brake-piping/to-jun-72

 

The later ones are called a NP valve (46223-N3300 from 7207 - 73010.

 

http://www.carpartsmanual.com/datsun/Z-1969-1978/brake/brake-piping/from-jul-72

 

The “T” connector is shown in both links, is between the proportioning valve and the brakes. 

 

To the best of my knowledge, the early valve cannot be rebuilt.  They can get clogged/frozen and block the flow of fluid to the brakes (ask me how I know).  If you find one, clean it carefully with brake cleaner to ensure fluid passes thru it but don't try to disassemble as you can damage the spring-loaded valve.

Edited April 4, 2016 by jfa.series1