Mikey Posted October 6, 2009 Share Posted October 6, 2009 So on my 73 Z, ive got a msa stage 2 front brake setup ( toyota truck binders, large spaced rotor, stainless steel lines) and in the rear ive got 240sx calipers and 280zx rotors. now it was too rear biased when i put the 240sx rears on and i got myself a wilwood bias valve. i installed it and went to tune it and with the knob half way in teh rear brakes were locked like i had the parking brake on. so i dialed it all the way out and its almost right but its still too rear biased, when the tires lock the rears lock up first? any idea on why this is still too rear biased or a solution to my problems? Thanks in advance Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 6, 2009 Share Posted October 6, 2009 i installed it and went to tune it and with the knob half way in teh rear brakes were locked like i had the parking brake on. so i dialed it all the way out and its almost right but its still too rear biased, when the tires lock the rears lock up first? What you're saying here doesn't make a lot of sense. The valve doesn't apply the brakes. All it does is change the pressure going to the rears. If you cranked it up then it should reduce the pressure going to the rears when you step on the pedal. It sounds like you have something else funky going on. Quote Link to comment Share on other sites More sharing options...
Mayolives Posted October 6, 2009 Share Posted October 6, 2009 The proportioning valve is relatively sensitive and by dialing the valve all the way in one direction, you should be locking the front brakes not just reducing the input to the rears. What are you using for master cylinders? Do you have separate ones for front and rear? Was the valve new when installed? Have you tried to re-bleed the brakes? Quote Link to comment Share on other sites More sharing options...
mark Posted October 6, 2009 Share Posted October 6, 2009 Do you still have the stock proportioning valve in line? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 6, 2009 Share Posted October 6, 2009 Wait a minute... you didn't put it in the front brake system, did you? If so, take it out and put it in the rear brakes. You DO NOT want a prop valve in the front brakes. Quote Link to comment Share on other sites More sharing options...
ktm Posted October 7, 2009 Share Posted October 7, 2009 You have 240sx calipers in the rear but are using a 280zx rotor? What bracket did you use to attach the caliper? This swap commonly uses the 300zx rear rotor with the 240sx calipers. You say MSA Stage 2 front brake upgrade, is that with vented or solid rotors? What brake pads are you using? Did you remove the stock proportioning valve located in the rear of the car? Quote Link to comment Share on other sites More sharing options...
Mikey Posted October 7, 2009 Author Share Posted October 7, 2009 Ok let me start off with thanks for all the replies... What you're saying here doesn't make a lot of sense. The valve doesn't apply the brakes. All it does is change the pressure going to the rears. If you cranked it up then it should reduce the pressure going to the rears when you step on the pedal. It sounds like you have something else funky going on. thats what i was thinking but there wasnt any problem before this. The proportioning valve is relatively sensitive and by dialing the valve all the way in one direction, you should be locking the front brakes not just reducing the input to the rears. What are you using for master cylinders? Do you have separate ones for front and rear? Was the valve new when installed? Have you tried to re-bleed the brakes? right, its just limiting the pressure. im using a new oem master cyl. valve is brand new. re bled the master cyl and the brakes. Do you still have the stock proportioning valve in line? no i do not. i "gutted" it by instruction of a local grassroots racer. Wait a minute... you didn't put it in the front brake system, did you? If so, take it out and put it in the rear brakes. You DO NOT want a prop valve in the front brakes. no its in the rear section. You have 240sx calipers in the rear but are using a 280zx rotor? What bracket did you use to attach the caliper? This swap commonly uses the 300zx rear rotor with the 240sx calipers. You say MSA Stage 2 front brake upgrade, is that with vented or solid rotors? What brake pads are you using? Did you remove the stock proportioning valve located in the rear of the car? modern motorsports caliper adapter. it might be 300zx rotors. its been a while. front rotors are drilled/slotted. pads are standard semi metalic pepe boys pads. i did not remove the prop valve in the back of the car. only the one on the firewall was "gutted" Thanks again for the help. Quote Link to comment Share on other sites More sharing options...
Zmanco Posted October 7, 2009 Share Posted October 7, 2009 I have the same setup as you if you're using 300zx rotors in the rear, but I find that unless I use a rear pad with a higher coefficient of friction than the front, even with the prop valve all the way open, I get front lockup first. While I don't see how the stock prop valve could cause the rears to lock first, still I'd remove it just to get one more variable out of the equation. Also, I would suggest you pay more attention to the pads you choose. My own limited experience is that the pad materials have MORE EFFECT on the overall brake performance than the calipers and rotors. If you don't know what brand of pads you have front and rear, then that could also be an issue, although if turn the rear pressure down with the prop valve, it should prevent the premature locking you describe. If that doesn't work, then I think you have to go back (again) and really confirm that you have the adjustable prop valve in the rear circuit and not the front. Quote Link to comment Share on other sites More sharing options...
Mikey Posted October 7, 2009 Author Share Posted October 7, 2009 I have the same setup as you if you're using 300zx rotors in the rear, but I find that unless I use a rear pad with a higher coefficient of friction than the front, even with the prop valve all the way open, I get front lockup first. While I don't see how the stock prop valve could cause the rears to lock first, still I'd remove it just to get one more variable out of the equation. Also, I would suggest you pay more attention to the pads you choose. My own limited experience is that the pad materials have MORE EFFECT on the overall brake performance than the calipers and rotors. If you don't know what brand of pads you have front and rear, then that could also be an issue, although if turn the rear pressure down with the prop valve, it should prevent the premature locking you describe. If that doesn't work, then I think you have to go back (again) and really confirm that you have the adjustable prop valve in the rear circuit and not the front. well i know there just generic semi metalic pads IIRC "prostop" brand. and i put my prop valve very similar to this setup http://i51.photobucket.com/albums/f380/rontyler/Pro1.jpg but i used the line out of the splitter like this http://forums.hybridz.org/attachment.php?attachmentid=11342&d=1231570198 I guess ill just take a picture later when im home. Quote Link to comment Share on other sites More sharing options...
Mikey Posted October 8, 2009 Author Share Posted October 8, 2009 anyone else have any ideas? Quote Link to comment Share on other sites More sharing options...
ktm Posted October 8, 2009 Share Posted October 8, 2009 The front valve is not a prop valve. It is a switch that senses pressure differential between the front and rear circuit. The prop valve is under the car back by the passenger wheel, bolted to the rear deck. Quote Link to comment Share on other sites More sharing options...
mark Posted October 8, 2009 Share Posted October 8, 2009 If you gutted the switch you are screwed. You just merged two brake circuts into one. Replace the switch and gut the rear proportioning valve. Quote Link to comment Share on other sites More sharing options...
Nigel Posted October 9, 2009 Share Posted October 9, 2009 Guys... THERE IS NO REAR PROPORTIONING VALVE ON A '73 240Z!!! Remember that! I've seen this happen over and over again, where owners of earlier Z's advise later Z owners to just gut the prop valve, assuming it's still located at the rear of the car. Bad idea! Here's why... I'm not sure exactly when it started, but probably from the beginning of the '73 model year, Nissan moved the proportioning valve to the firewall. Furthermore, it does not operate in the same fashion as the earlier valves. With the '73 and later (not sure if this includes all model years for the 280Z), the brake pressure to the front, right caliper modulates the pressure to the rear brakes. If you GUTTED the valve on the firewall, you've tied the front right and the rear brake lines together! This is not good! What you need to do is REMOVE the valve, and splice the gap in the lines together. Make sure you tie the correct lines together. The top lines connect together, and the bottom lines connect together. You can see this done in this picture linked to earlier (look at the brass fittings splicing the brake lines together on the firewall) ... The brake pressure switch that others are talking about is located on the inner driver's side front fender, below the master cylinder. Don't touch that. If you've gutted it, then as mentioned, you will have also tied the front and rear brake lines together. Nigel '73 240ZT Quote Link to comment Share on other sites More sharing options...
Mikey Posted October 9, 2009 Author Share Posted October 9, 2009 Guys... THERE IS NO REAR PROPORTIONING VALVE ON A '73 240Z!!! Remember that! I've seen this happen over and over again, where owners of earlier Z's advise later Z owners to just gut the prop valve, assuming it's still located at the rear of the car. Bad idea! Here's why... I'm not sure exactly when it started, but probably from the beginning of the '73 model year, Nissan moved the proportioning valve to the firewall. Furthermore, it does not operate in the same fashion as the earlier valves. With the '73 and later (not sure if this includes all model years for the 280Z), the brake pressure to the front, right caliper modulates the pressure to the rear brakes. If you GUTTED the valve on the firewall, you've tied the front right and the rear brake lines together! This is not good! What you need to do is REMOVE the valve, and splice the gap in the lines together. Make you you tie the correct lines together. The top lines connect together, and the bottom lines connect together. You can see this done in this picture linked to earlier (look at the brass fittings splicing the brake lines together on the firewall) ... The brake pressure switch that others are talking about is located on the inner driver's side front fender, below the master cylinder. Don't touch that. If you've gutted it, then as mentioned, you will have also tied the front and rear brake lines together. Nigel '73 240ZT THATS IT!!! i gutted the valve on teh firewall as pictured. no wonder it wont work for ♥♥♥♥. yeah i know the valve in the front should be left alone... well now i feel dumb.. after i patch the two lines together should it all work properly? Quote Link to comment Share on other sites More sharing options...
ktm Posted October 9, 2009 Share Posted October 9, 2009 Nigel, I knew that the 260z and 280zs had the prop valve in the front. I mistakenly assumed that all 240zs had the prop valve in the rear. Thanks for the clarification. Quote Link to comment Share on other sites More sharing options...
Zmanco Posted October 9, 2009 Share Posted October 9, 2009 well now i feel dumb.. after i patch the two lines together should it all work properly? Those pictures are from my 73 so I think you'll be on the right track. And I'll put another plug in to spend some time researching brake pad materials and choose based on how you plan to drive the car (daily driver vs. 1/4 mile vs. canyon carver/road course). Quality pads are going to make at least as much contribution to improving stopping distance and fade resistance as just bolting on hardware. Quote Link to comment Share on other sites More sharing options...
Mikey Posted October 9, 2009 Author Share Posted October 9, 2009 yeah i very much so agree with that. and where did you find the m10x1.25 unions? i cant find them anywhere Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 9, 2009 Share Posted October 9, 2009 Aren't they 10 x 1? Quote Link to comment Share on other sites More sharing options...
Mikey Posted October 10, 2009 Author Share Posted October 10, 2009 it was mentioned in another thread that the fittings were m10x1.25 i have not taken it off and tried. might be worth a try Quote Link to comment Share on other sites More sharing options...
ktm Posted October 10, 2009 Share Posted October 10, 2009 They are M10x1. Flying Miata carries them if I remember correctly. Quote Link to comment Share on other sites More sharing options...
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