RS Speed Posted November 11, 2009 Share Posted November 11, 2009 Are most people plumbing these valves into the rear lines enabling them to decrease rear line pressure? reason I ask is because I would like to INCREASE rear line pressure but I always see people installing it in the rear which means people are reducing the rear line pressure. My car is finally breaking like it should and I am happy so far but I was thinking I could get it to brake a bit better since the front are locking wayyyy sooner that the rears still. So I guess I would have to install the valve inline going to the splitter on the driverside frame rail to decrease my front line pressure so the rears can catch up a bit.... anyways heres a quick rundown of my system, just wondering if anyone else has one installed on the front lines. 1971 240z 280zx 15/16 master stock proportioning valve on frame rail removed rear pressure valve thing for drum brakes near rear tee vented 4x4 brakes up front (ceramic pads) maxima brakes in rear (semi-metallic, im thinking ceramic in the rear would help with my problem too but lets ignore this for now) Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 11, 2009 Share Posted November 11, 2009 Do NOT install a prop valve in the front brakes. The valve has a knee in it and it is NOT actually proportional. The harder you press the brakes, the less effort you get out of the braking circuit that has the valve in it (compared to the one without--in other words, they aren't linear). That works well in the rear because weight transfers off the rear under braking and you actually need less effort in the rear under heavy braking than under light braking. In the front the reverse is true, so you'd get more rear braking as you stepped harder and harder on the brakes with a prop valve in the front. That's a recipe for disaster. A good solution would be to go to a dual master setup and get a smaller master for the rear, or play with pad compounds etc. http://www.stoptech.com/tech_info/wp_proportioning_valves.shtml Quote Link to comment Share on other sites More sharing options...
RS Speed Posted November 11, 2009 Author Share Posted November 11, 2009 Makes sense, I was unsure on the topic so I though I would make this thread. Does the 15/16 280zx master cylinder split the front and rear pressure equally or does the front get more fluid? Would reversing the front and rear reservoir lines to the splitter on the frame rail change to a more rear biased setup? Lastly does the splitter on the driver frame rail have any restriction/proportioning of its own or is it simply flowing fluid to the correct lines. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 11, 2009 Share Posted November 11, 2009 The front and rear lines get the same amount of fluid at the same pressure. The reservoir for the front brakes is larger because the pistons are larger and as the brake pads wear the fluid level gets lower faster. The block in the front is just a distribution block with a pressure sensor so that the brake light on the dash will come on if either the front or rear brakes are getting more pressure than the other end. The factory proportioning valve is in the back on your car. It is part of the T that splits the rear brake line to each wheel. It's up near the frame rail at the front of the right rear wheel well. You can gut it, and then use a proportioning valve there, and possibly that's all you need. If opening the adjustable valve all the way doesn't have the desired effect, then I think you really need to look at pad compounds or duals. Quote Link to comment Share on other sites More sharing options...
RS Speed Posted November 11, 2009 Author Share Posted November 11, 2009 I have already bypassed the said valve you are talking about in the rear rather than gutting it. If you notice in my first post I mentioned my rear pads are less grabby than the fronts, I just wanted a clear understanding of whats going on but my first step was going to be ceramic pads in the rear then see where it goes. Thanks for the help bud. Quote Link to comment Share on other sites More sharing options...
Zmanco Posted November 11, 2009 Share Posted November 11, 2009 I have a similar setup to yours except with 240sx calipers in the rear and could only get a good balance by going to a pad in the rear with a higher coefficient of friction. I believe the 240sx calipers and 300zx rotors have a slightly larger diameter than the Maxima setup so I suspect you will have the same issue as well, perhaps a little more so. Quote Link to comment Share on other sites More sharing options...
RS Speed Posted November 11, 2009 Author Share Posted November 11, 2009 Good to know I'm not the only one. I'm currently running some weak pads, whatever came loaded in the caliper, so I'm hoping I could see some improvement with a decent pad in the rear. Thanks for the input. Quote Link to comment Share on other sites More sharing options...
HLS30-08077 Posted November 11, 2009 Share Posted November 11, 2009 Good to know. I did the non-vented rotors and Toyota 4-piston calipers up front but still have the stock MC and drums brakes in the rear on my 70' and everything is well balanced. And the pads are your everyday regular pads. But the 260Z has the 15/16" MC, S12-8 4-piston calipers and non-vented rotors up front, and the rears are the 79' to 81' 280ZX rear disc brake set-up, with regular bendex pads and rotors. Nothing slotted or drilled, no special compounds or anything like that. It's just a basic set-up for now. I can't even tell you how it performs until next spring when it hits the road for the first time in 2 years. But I will definately give updates and progresssive reports on the pros and cons of this set-up. Thanks again Jon, you da man! as always, Dave Quote Link to comment Share on other sites More sharing options...
RS Speed Posted November 11, 2009 Author Share Posted November 11, 2009 hey my Z is a 10/70 production date HLS30-11xxx, I wish i was under the 10k mark Quote Link to comment Share on other sites More sharing options...
ktm Posted November 14, 2009 Share Posted November 14, 2009 The factory proportioning valve is in the back on your car. It is part of the T that splits the rear brake line to each wheel. It's up near the frame rail at the front of the right rear wheel well. Correct. You can gut it, and then use a proportioning valve there, and possibly that's all you need. Another solution is to simply install a union there and then install the bias valve up by the master cylinder on the rear circuit before the brake bias switch. If opening the adjustable valve all the way doesn't have the desired effect, then I think you really need to look at pad compounds or duals. This was my main concern when installing my setup. I researched for hours about the 240sx/S12W combo and heard people complaining about bias issues when using the same pad compound front and rear. I have Porterfield R4S' in the front and KVRs in the rear. If I open the valve fully, the rears lock up. I need to back off 1.5 to 2 turns (IIRC) in order for the fronts to just lock before the rears. Quote Link to comment Share on other sites More sharing options...
RS Speed Posted November 16, 2009 Author Share Posted November 16, 2009 hmmm i must have read through and missed something earlier. You mention the splitter is the acutal proportioning valve and I mentioned I bypassed it. What I meant was I bypassed that little valve right before the tee (i believe it has something to do with holding pressure for drum brakes) So there is a proportioning valve in the T itself which splits the rear circuit to left/right? If so Im gonna gut that puppy and see if it starts putting more pressure on the rear, then I could always run a valve to reduce the rear pressure if its locking early. Can you confirm its the splitter T in the rear that does the proportioning and not the little thing right before the T which I bypassed? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 16, 2009 Share Posted November 16, 2009 The T is the prop valve. It has a bolt in it. Take that out and you'll see that it is a needle/spring setup. Cut it off, reinstall the bolt. You've now gutted your prop valve. Or just put the adjustable one in right there and use a universal T on the other end, you'll need to be able to find the right fittings or re-flare the tubing to work with SAE fittings that fit the T you buy. Quote Link to comment Share on other sites More sharing options...
RS Speed Posted November 16, 2009 Author Share Posted November 16, 2009 That's awesome so there is hope after all. Do you think I should just gut it first and see if there is too much brakes in the rear and then see if I need the prop valve. Or is it going to be way to much pressure in the rear from your personal experience. Thanks btw you have been a great help Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 16, 2009 Share Posted November 16, 2009 Safe way is to put the prop valve in first, and then if you can't get enough rear brakes take it out or play with pads. I'd be inclined to leave it in and play with pads. Quote Link to comment Share on other sites More sharing options...
RS Speed Posted November 16, 2009 Author Share Posted November 16, 2009 I was planning on doing pads anyways, I might as well do that first and adjust based on that. Got any recommendation for rear pads, Its for 85 maxima calipers (same as 240sx I believe) I was thinking about hawk ht-10 Also does a pad generally overheat or is a disc more prone to overheating on the track. I've got motul brake fluid, cooling ducts pivoting with the rotor and vented rotors which are crossdrilled. I'm not sure if the disc is too small and maybe that's the guy causing the fade? Maybe its a shiesty rotor I got off ebay which some guy is crossdrilling in his bathroom? Maybe its because the rear isn't doing enough and the front is getting overworked? I just want to sort out all bugs in the braking system. I'm relatively new to racing on an actual track and the braking demand at button willow in certain configurations really plays a toll on my braking system. The track really brings out the flaws in a car but I'm loving the challenge. I just don't have pockets deep enough to buy everything I wan't at once lol Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 16, 2009 Share Posted November 16, 2009 I was planning on doing pads anyways, I might as well do that first and adjust based on that. Got any recommendation for rear pads, Its for 85 maxima calipers (same as 240sx I believe) I was thinking about hawk ht-10 Also does a pad generally overheat or is a disc more prone to overheating on the track. I've got motul brake fluid, cooling ducts pivoting with the rotor and vented rotors which are crossdrilled. I'm not sure if the disc is too small and maybe that's the guy causing the fade? Maybe its a shiesty rotor I got off ebay which some guy is crossdrilling in his bathroom? Maybe its because the rear isn't doing enough and the front is getting overworked? I just want to sort out all bugs in the braking system. I'm relatively new to racing on an actual track and the braking demand at button willow in certain configurations really plays a toll on my braking system. The track really brings out the flaws in a car but I'm loving the challenge. I just don't have pockets deep enough to buy everything I wan't at once lol Buttonwillow is tough on brakes, especially if you're going clockwise and using the hairpin before the esses. I punched a hole through the back of a brake pad with the piston at the end of the bus stop: I think pads are the most common problem and the right pad can make a huge difference. Brake fade where you step on the brakes and the pedal feels fine but the car doesn't slow down any more is probably the most common problem. Then you have pad "chunking" where large parts of the friction material come off, basically the pad overheats and starts to break apart. After that it's boiling the fluid, when it boils it becomes compressible, so the pedal suddenly goes to the floor (done that several times at Buttonwillow too). To fix this you need more heat capacity (bigger thicker heavier rotors) or more ability to shed heat (ducts). Rotor issues are pretty uncommon, except for cracking between the holes of cross drilled rotors. Don't worry if you see cracks, they don't really matter until the bridge the span between one hole and another, then it's time to replace them. I think a lot of brake issues can be solved with the right pads. Hopefully someone more in the know will come up with some recommendations for you. I ran R4's and R4S's and that was it so my experience is pretty limited. I did like the R4 pads, the R4S wasn't suited to track use as can be seen in the photo. Quote Link to comment Share on other sites More sharing options...
RS Speed Posted November 16, 2009 Author Share Posted November 16, 2009 First time out at button we ran the short route to the esses and we didnt run the dogleg on the back straight. I personallly like this configuration, it had more technical turns and less stress on the brakes. I had the L28 at the time with drums in the rear and regular pads up front and I managed 4 laps before the brakes would fade. This was the type where the pedal felt fairly normal but the car just was NOT slowing down. Second time out there we ran the long straight in the rear and the long straight to the hairpin for the esses. Granted I was running the RB25 this time around my brakes faded at the end of the FIRST lap, barely stopping in time for the hairpin. I knocked the boost down to 8 psi and pretty much ran the course braking really early the rest of the day. I'd love to run some kind of a bracket and a larger front rotor but I can seem to find one available, I guess I'm gonna try some rear pads, prop valve and go from there. I just hate burning 400 on track days where I can't have fun because of mechanical limitations. Quote Link to comment Share on other sites More sharing options...
93anthracite Posted December 21, 2009 Share Posted December 21, 2009 Safe way is to put the prop valve in first, and then if you can't get enough rear brakes take it out or play with pads. I'd be inclined to leave it in and play with pads. I'm reading up on my own ideas for running new piping throughout my car and stumbled upon this thread. It seems to me that another, more driver-adjustable solution, might be to run a simple T from the back (or gut the stock one), run a new line from there to the interior of the cabin and plumb in an adjustable prop valve near the driver on the trans tunnel, then run it back into the trans tunnel or engine bay. This would put the valve within reach of the driver, giving the ability to adjust on the fly. Quote Link to comment Share on other sites More sharing options...
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