vashonz Posted March 9, 2007 Share Posted March 9, 2007 I just installed 12" wilwoods and 240sx disks in my 240, I cleared out the residual pressure valve in the back. And am now getting ready to install an inline adjustable proportioning valve. My question is if I clear out (remove piston and spring) from the stock proportioning valve is this "REALLY BAD"? The master cylinder has 2 lines running to the proportioning valve, and it would seem that the moveable piston inside the valve keeps the front and rear parts of the brake system seprate. If I remove the pison it will effectively make it so from the master cylinder into one BIG cylinder. If that happens I why does it matter which resovioir on the master cylinder goes to the front and to the rear? Should I just install a "T"(in place of the stock proportioning valve) and separate the front and rear systems completely? Sorry if this is confusing, I have trouble putting things into words. I'll draw a picture later when I have more time. Quote Link to comment Share on other sites More sharing options...
260DET Posted March 9, 2007 Share Posted March 9, 2007 Separate front and rear brake circuits are a safety innovation, probably required by law anyway. An adjustable proportioning valve plumbed into the single line going to the rear brakes would still work either way. The usual thing is to replace the stock prop valve with a (three way) T piece. Quote Link to comment Share on other sites More sharing options...
vashonz Posted March 9, 2007 Author Share Posted March 9, 2007 Heres a quick picture of what I was thinking. Quote Link to comment Share on other sites More sharing options...
katman Posted March 9, 2007 Share Posted March 9, 2007 That's the brake warning circuit, and gutting it will result in pumping all the fluid from the front brakes into the rear of the brake master cylinder. You will end up with no brake and a big mess. What year is your car? The stock proportioning valve is in a different place depending, but your Tee idea is on the right path. Quote Link to comment Share on other sites More sharing options...
johnc Posted March 9, 2007 Share Posted March 9, 2007 If you're installing an adjsutable prop valve, you need to remove that brake line switch and the factory prop valve. As Katman said, its in different places on the car depending on the year, but its most likely in back above the diff. Quote Link to comment Share on other sites More sharing options...
Roostmonkey Posted March 9, 2007 Share Posted March 9, 2007 Daves directions for installing his rear brake setup says to leave the stock prop valve. I'm confused... (AZ Dave ) Quote Link to comment Share on other sites More sharing options...
johnc Posted March 9, 2007 Share Posted March 9, 2007 Everyone has different opinions about brakes and porportioning. I prefer to simplify things and run only run pressure based prop valve in the brake system. OEM brake system engineers and the folks at Stop Tech feel the same way: 1. If you have the deeply-rooted need to install your own adjustable proportioning valve, be advised that they should NEVER be installed if the factory unit is still in place. Proportioning valves in series with one another can do nasty, unpredictable things! http://www.stoptech.com/tech_info/wp_proportioning_valves.shtml Quote Link to comment Share on other sites More sharing options...
Roostmonkey Posted March 9, 2007 Share Posted March 9, 2007 Thanks John, thats a good read.It makes alot of sense. I'm glad this came up now because I just recieved Daves rear brakes to match the fronts I put on last year.I also installed the willwood prop valve with the fronts.I never got a chance to really test things out (track day) so I have no clue where the bias is.When I put the rears on, I'll gut the stock valve and tune with the willwood. Quote Link to comment Share on other sites More sharing options...
vashonz Posted March 9, 2007 Author Share Posted March 9, 2007 I already stripped the inside out of this (located above the diff on the passenger side), but I thought that was the 10# back pressure valve. But I thought wrong. Then: Before I forget, Have you removed the brake bias bar (pressure regulating valve) in the rear brake system in your Z yet. It is the one just before the T-bar (3-way tube connector) above the rear axles. If you haven't then you need to. What this does is keep some pressure on the rear brakes after you release the brake pedal. It helps to keep from locking up the rear brakes before the fronts. But it is designed for the drum brakes and not for disc brakes. You can add a brake bias valve (you can adjust by yourself) in the system, if you like (most people do). I have the 300ZX brakes upfront and 280ZX brakes in the back. I took out the valve out of the system and bent the line over and reconnected it. I do not have a self adjuster in it at this time. I do have good brakes that pull down even on a hard brake. I like it this way and race it this way. You can do it both ways, it is up to you and your taste. Good Luck, Rich. Is he describing the same piece? or is there somthing else down there. The only other thing I saw was the distribution block (inlet - R outlet - L outlet) There is only one on a US version 240. There is a plug in the side of it. You unscrew it and you'll see that it has a long needle with a spring on it. Cut that part off, and screw it back in. That's it. This is what I was looking for, reassurance that I had found all the valves. Quote Link to comment Share on other sites More sharing options...
gnosez Posted March 11, 2007 Share Posted March 11, 2007 JohnC - "If you're installing an adjsutable prop valve, you need to remove that brake line switch and the factory prop valve" I gutted my prop valve but I'm wondering what you mean by brake line switch. Quote Link to comment Share on other sites More sharing options...
1 tuff z Posted March 11, 2007 Share Posted March 11, 2007 johnc, i'm running the modern motorsports brake setup-13'' front with the 240sx rear calipers. removed both the [factory] safety valve and prop valve and installed a wilwood prop valve inline going to the rear brakes. upon initial drive i had way too much front bias. stopped and increased the rear bias-the long and short-i opened the valve all the way and still too much front. wound up getting a more aggressive pad compound for the rears and my bias is pretty good now [both street and track]. i contacted a number of brake retailers and no one could come up with a solution other than adjusting thru brake pads. i even went so far as to remove the prop valve [this actually resulted in a bit more rear brake-but still not enough till i swapped in the new pads]. my car is a 4/73 vintage, 13" modmsports extreme rotors front and the 300zx rear rotors. running the pads ross sent in the front and hawk hp+ in the rear. Quote Link to comment Share on other sites More sharing options...
MrFancypants Posted March 11, 2007 Share Posted March 11, 2007 Im also fixing to put one of these in. Is there any reason to go with the lever style over the knob style? Im also wondering if it's really that necessary to route everything into the cabin or if I should just install it on the firewall right next to the booster/MC where the stock prop valve goes. I was also thinking of using the same location as Pop (there's that nice rubber grommet right under there), but that would require running lines into the trans tunnel. I would think you can leave the stock bias warning sensor in place, but since I am replacing everything I just tore it out. - Greg - Quote Link to comment Share on other sites More sharing options...
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