240zdan Posted March 5, 2016 Share Posted March 5, 2016 (edited) Did a bit of searching, couldn't find a definitive answer. My setup is as follows: GTR 4 piston fronts with GTR vented rotors s13 rears with z31 non vented rotors. Right now I am running the original prop valve in the rear, as well as the original "differential valve" in the engine bay. I am looking for more rear bias. Shoudl I retain the original "differntial valve in the engine bay and install an inline wilwood prop for the rear? Or should I remove the OEM rear prop valve as well as the differential valve and install a willwood 260-11179 in its place? What is the purpose of the original differntial valve in the engine bay? Right now I am noticing my front left caliper is much stronger than my front right, no leaks or seized pistons. Edited March 5, 2016 by 240zdan Quote Link to comment Share on other sites More sharing options...
Miles Posted March 6, 2016 Share Posted March 6, 2016 (edited) Don't do anything. A PV would only be required if the rear brakes were more effective than the front brakes. That is "rear biased". Almost all of the so called front - rear disk "upgrades" result in too much front brake bias. So installing a PV is counter intuitive. The differential pressure safety switch turns on a red light on the dash if there is a leak in the front or rear brake circuits. All that happens is the piston inside moves to the low pressure side if there is a leak on that side and turns on the red light. That is it. Removing the differential pressure safety switch does not improve anything. Leave it alone. If one front caliper is working better than the other caliper, then the caliper on the other side is defective. A number of things can cause this, usually a stuck piston or a leaking seal. Edited March 6, 2016 by Miles Quote Link to comment Share on other sites More sharing options...
240zdan Posted March 6, 2016 Author Share Posted March 6, 2016 (edited) Don't do anything. A PV would only be required if the rear brakes were more effective than the front brakes. That is "rear biased". Almost all of the so called front - rear disk "upgrades" result in too much front brake bias. So installing a PV is counter intuitive. The differential pressure safety switch turns on a red light on the dash if there is a leak in the front or rear brake circuits. All that happens is the piston inside moves to the low pressure side if there is a leak on that side and turns on the red light. That is it. Removing the differential pressure safety switch does not improve anything. Leave it alone. If one front caliper is working better than the other caliper, then the caliper on the other side is defective. A number of things can cause this, usually a stuck piston or a leaking seal. Appreciate your response. I am removing the rear pressure regulating valve (located in the rear of the car on early cars and in the engine bay on later). Are you saying that with this valve removed, and full flow going to the rears, my setup will be still front biased and the rears will not lock? Would be pretty crazy if that were true. So since that brake switch just triggers a warning light, I will remove it and get the 260-11179 . Edited March 6, 2016 by 240zdan Quote Link to comment Share on other sites More sharing options...
johnc Posted March 6, 2016 Share Posted March 6, 2016 Most likely your setup without a prop valve will still be front biased. Quote Link to comment Share on other sites More sharing options...
240zdan Posted March 6, 2016 Author Share Posted March 6, 2016 (edited) Most likely your setup without a prop valve will still be front biased. Im ok with that, I'll upgrade the rears down the road. But removing the stock prop valve and installing an adjustable one will help the situation, correct? Is this the valve right here, below the three way tee? My Main question here was whether or not I can remove the stock brake switch/splitter. From the looks of it I can. Edited March 6, 2016 by 240zdan Quote Link to comment Share on other sites More sharing options...
Miles Posted March 6, 2016 Share Posted March 6, 2016 As long as your brake set up is front biased, installing a pressure limiting device on the rear brake circuit would not do anything to improve the problem. Remember a PV can not raise the brake pressure - it limits it. The so called brake upgrades for our Z cars (Toyota - Maxima, Toyota - 240SX etc.) typically result in a front to rear ratio of 60f/40r to 70f/30r. The only way you can have a balanced brake system is to design it by the numbers taking into consideration factors such as master cylinder size, brake rotor diameter, number of pistons in the caliper, pad friction coefficient etc. If you do the brake torque calculations you will see what I mean. Yes, you can replace the brake pressure differential valve (aka brake switch) with a three-way connector as shown in the attached picture. Do not consider "gutting" the switch as you would be connecting the front and rear brake circuits together. Anything you change will have a domino effect because brake systems are engineered to work as a system. There are many many threads here dealing with brake bias issues. You may want to study them before making any changes to your brake system. Quote Link to comment Share on other sites More sharing options...
240zdan Posted March 6, 2016 Author Share Posted March 6, 2016 (edited) As long as your brake set up is front biased, installing a pressure limiting device on the rear brake circuit would not do anything to improve the problem. Remember a PV can not raise the brake pressure - it limits it. The so called brake upgrades for our Z cars (Toyota - Maxima, Toyota - 240SX etc.) typically result in a front to rear ratio of 60f/40r to 70f/30r. The only way you can have a balanced brake system is to design it by the numbers taking into consideration factors such as master cylinder size, brake rotor diameter, number of pistons in the caliper, pad friction coefficient etc. If you do the brake torque calculations you will see what I mean. Yes, you can replace the brake pressure differential valve (aka brake switch) with a three-way connector as shown in the attached picture. Do not consider "gutting" the switch as you would be connecting the front and rear brake circuits together. Anything you change will have a domino effect because brake systems are engineered to work as a system. There are many many threads here dealing with brake bias issues. You may want to study them before making any changes to your brake system. I am talking about removing the rear pressure restrictor under the car located in the rear. I have posted a pic, please take a look. As far as I know this is the stock proportioning valve, or restrictor. Youve mentioned twice already that installing a proportioning valve cannot increase the pressure going to the rear brakes. I fully understand that, this is quite an obvious fact. However, by removing the "restrictor" which I have posted a picture of, I effectively have full flow going to the rear brakes. An adjustable prop valve will let me dial it down should I need to or if I decide to upgrade the rear brakes in the future. Again, I am fully aware that a prop valve can only decrease pressure. Please take a look at the photo I have posted. Since removing the "brake"switch" has no negative effects, I will be buying the willwood 260-11179 to replace it entireley, which has a prop valve built in. I will then discard of the original prop valve under the car. This was my question all along, the issue due to having too small rear brakes are a separate issue, and I will deal with that when the time comes. I have gotten the information I needed from this topic. Edited March 6, 2016 by 240zdan Quote Link to comment Share on other sites More sharing options...
240zdan Posted March 6, 2016 Author Share Posted March 6, 2016 (edited) Another pic, I will be removing 10 and using the willwood in place of 8 to control bias. I will upgrade the rear brakes should I see fit. I am certain that removing 10 and installing an adjustable valve, should it even need to be fully open, will improve the rear bias. It may still be forward biased, but it will be better. I should have just asked what does the brake differential switch do and can I get rid of it, would have been much simpler. Edited March 6, 2016 by 240zdan Quote Link to comment Share on other sites More sharing options...
Miles Posted March 6, 2016 Share Posted March 6, 2016 Sounds good. Quote Link to comment Share on other sites More sharing options...
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