subtle_driver Posted December 15, 2011 Share Posted December 15, 2011 I have a set of vented 300zx rotors from a z31 with spacers from zrace products and 4-piston toyota 4-runner calipers up front, and in the rear, 240sx non-abs rear calipers and non-vented z31 rotors. The master cylinder is a 1979 280zx unit. problem is I am locking the fronts up too easily. I need to make the rear brake bias percentage higher than what they are now. How do i go about this? I am thinking to bypass the stock proportioning valve and install an adjustable willwood unit for the rear brakes. I do a lot of autocross and rallycross with this car. and i drive mountain roads to work every day. i want to dial in the brakes so it will stop better and be safer and improve my autocross times. it seems to me like they are 90% front almost. i know if i can bring more braking power to the rear i will knock off a few seconds from my times and make it more predictable. i miss the stock brakes as it would stop perfectly till you overheated them.... I am looking for a few different options. please don't reply unless you have done this yourself. thanks! Quote Link to comment Share on other sites More sharing options...
beermanpete Posted December 15, 2011 Share Posted December 15, 2011 Using an adjustable proportioning valve should solve your problem. This will allow to adjust from no rear brake pressure reduction to about 50% reduction. If you still cannot get the bias you want you will need to rethink the brake system design. Quote Link to comment Share on other sites More sharing options...
h4nsm0l3m4n Posted December 15, 2011 Share Posted December 15, 2011 You should search a bit more, there are a lot of people on this site, including myself, that run similar, or identical, brake setups. From my experience even with the proportioning valve fully open (no pressure reduction) the fronts lock up much earlier than the rears. I would consider running more aggressive brake pads in the rear to get more rear brake bias and use an adjustable proportioning valve to fine tune the split. Quote Link to comment Share on other sites More sharing options...
Miles Posted December 15, 2011 Share Posted December 15, 2011 (edited) I installed a Wilwood proportioning valve when I did the Toyota vented 4x4 and 240SX swap on my 240Z. I have the proportioning valve wide open to the rears and the rear brakes still do not do much work. In an effort to improve performance I installed a 1" Wilwood MC, a larger 280Z booster and Porterfield R4-S pads. So far there is not much improvement. However, having the proportioning valve might come handy if you start experimenting with different pad combinations etc such as using more aggressive rear pads. One member I talked to said that he gets better performance, as compared to one of his cars with the Toyota-240SX swap, from stock front brakes, good pads, 240SX rears, and a 280Z booster. On another car he has stock brakes with a 280Z booster and sees better performance as comapred to the Toyota-240SX swap. Recently, I spent some time reading old posts for the Toyota-240SX swap and the front-rear bias problem is a common complaint. There were some posts indicating the swap works well for others. So there appears to be a solution. The Toyota-240SX swap doesn't appear to be a balanced system. If someone out there has a Toyota-240Sx swap that works well, i.e. more balanced, speak up. What did you do to resolve the bias problem? Edited May 8, 2017 by Miles Quote Link to comment Share on other sites More sharing options...
Kris.Is.Awesome Posted December 15, 2011 Share Posted December 15, 2011 Adjustable prop valve with a bias adjuster should do you well. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted December 15, 2011 Share Posted December 15, 2011 One member I talked to said that he gets better performance, as compared to one of his cars with the Toyota-240SX swap, from stock front brakes, good pads, 240SX rears, and a 280Z booster. On another car he has stock brakes with a 280Z booster and sees better performance as comapred to the Toyota-240SX swap. Similarly I got better results out of stock fronts and early 280ZX rear disc than I did with Toy 4x4 calipers on the front. With the Toy calipers I actually removed the prop valve and still had way too much front bias. One other thing you guys might look at is whether you can fairly easily put a different caliper with larger pads or pistons on the mount that you have. Quote Link to comment Share on other sites More sharing options...
Miles Posted December 16, 2011 Share Posted December 16, 2011 Re: Larger rear calipers Silvermine Motors (member owned) sells a big Mustang (2005?) rear caliper kit for the 240Z. http://www.silverminemotors.com/main.sc Quote Link to comment Share on other sites More sharing options...
h4nsm0l3m4n Posted December 16, 2011 Share Posted December 16, 2011 (edited) The silvermine motors says that their rear calipers use 1.6 in. pistons. The late S130s use 42.9 mm pistons or roughly 1.68 inches. Unless there is something else in the design of the caliper that I'm not aware of, its the size of the pad area and the larger diameter of the rotor on the Mustang setup that will yield any sort of improvement in braking, not piston diameter. I still feel the running a more aggressive pad in the rear will get the brake bias more even. Additionally an adjustable proportioning valve will allow you to fine tune the brake bias if you find that you now have too much brakes and are locking up the rears. Another thought would be possible using Z32 rear calipers with the MM 240sx caliper brackets. Arent the 240sx guys using these as a "bolt on" rear brake upgrade? If so it should be possible to get these to bolt onto our MM 240sx brackets. These calipers have a bigger piston diameter and a larger brake pad area. You will likely run into some issues getting the e-brake to work though and really at this point it may be better to just go with another off-the-shelf brake kit... Edited December 16, 2011 by h4nsm0l3m4n Quote Link to comment Share on other sites More sharing options...
ModernS30 Posted December 16, 2011 Share Posted December 16, 2011 Have you guys thought of every putting a prop valve on to limit the front brakes, not increase the rear brakes? If it is way to much brake, then limiting it a little bit shouldn't hurt a bit. Stock should be about 80% 20% anyways. Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted December 17, 2011 Share Posted December 17, 2011 Talk to the tech guy at Porterfield about your problem. Perhaps you can play with brake pad compound? Maybe go stickier compound in back? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted December 17, 2011 Share Posted December 17, 2011 Have you guys thought of every putting a prop valve on to limit the front brakes, not increase the rear brakes? If it is way to much brake, then limiting it a little bit shouldn't hurt a bit. Stock should be about 80% 20% anyways. It has been discussed before. VERY bad idea, because prop valves aren't proportional. They have a knee in them so that the harder you push on the brakes the less pressure goes to the side with the valve in it. If you put it in the front brake circuit, then when you really stomped on the brakes you'd get more and more rear braking vs front. Not good. More info: http://www.stoptech.com/technical-support/technical-white-papers/proportioning-valves Quote Link to comment Share on other sites More sharing options...
wheelman Posted December 17, 2011 Share Posted December 17, 2011 Which Toyota front caliper are you guys using? I'm running a vented front Toyota and Maxima rear setup and actually have to use an adjustable prop valve to reduce the rear bite. I think the Maxima calipers are essentially the same as the 280ZX units with a different e-brake setup, but don't quote me on it, they are bigger than the 240SX caliper though. Thing is I'm running the S12 vented front calipers not the S12W units. These calipers are the same as those used with the stock solid rotor but they are configured for use with a vented rotor. I'm also running a 1" master cylinder with a 280Z booster. Many guys say this doesn't work but I call BS on that. There is a little extra pedal effort but it makes for much easier modulation on the track. For pads I currently have cheap parts store units but they work pretty good for auto-x. Quote Link to comment Share on other sites More sharing options...
ModernS30 Posted December 18, 2011 Share Posted December 18, 2011 (edited) It has been discussed before. VERY bad idea, because prop valves aren't proportional. They have a knee in them so that the harder you push on the brakes the less pressure goes to the side with the valve in it. If you put it in the front brake circuit, then when you really stomped on the brakes you'd get more and more rear braking vs front. Not good. More info: http://www.stoptech.com/technical-support/technical-white-papers/proportioning-valves I see, this makes sense. Is it possible to make a valve that DOESN'T do this. I could see this being why the fronts lock and have some much more power than the rears. Maybe people are getting to stabby on the pedal rather than using a smooth threshold braking method? EDIT: I realized that might sound cocky, in no way is that what I mean for it to sound like. I am just trying to come up with solutions because I plan on running 4x4 vented brakes and I already have 82-83 zx rear calipers. Edited December 18, 2011 by ModernS30 Quote Link to comment Share on other sites More sharing options...
Miles Posted December 18, 2011 Share Posted December 18, 2011 (edited) One thing we want to avoid is creating a kluge by over complicating the brake system without understanding why the Toyota - 240SX swap isn't balanced. Kluge = an assortment of ill fitting parts forming a disgusting whole. What is needed is to find a solution as to why the Toyota 4x4 - 240SX combination doesn't work . It's not an engineered brake system to begin with. What would have to change to improve the performance of the Toyota 4x4 - 240SX swap? Things others have tried include more agressive pads, various front - rear pad combinations, larger master cylinder/booster combinations etc. And, of course, competent installation, bleeding, booster rod adjustment and etc. The 240SX rear brake set up is proportionly undersized when mated with the Toyota 4x4 front brakes. For example, my 91 4x4 4Runner had large drums on the rear so the front and rear brakes were better matched. A member (Edan, Silvermine Motors) seems to have come to the same conclusion, and came up with his big Mustang rear brake kit. So, go to a larger rear caliper/rotor combination or go back to a smaller front caliper/rotor combination for better front - rear balance. At this point I am considering going back to the smaller stock fronts with Porterfield R4-S pads, and a stock MC. I already have a 280Z booster and proportioning valve installed. Or doing the whole thing over with ArizonaZ brake kits. Edited May 8, 2017 by Miles Quote Link to comment Share on other sites More sharing options...
1 tuff z Posted December 18, 2011 Share Posted December 18, 2011 I experienced same issues with mine-modern motorsports 13" front and 240sx rear. Tried many things; more aggressive pads rear, remove stock prop valve & installed wilwood prop valve but no help [even removed wil prop valve-still too much front]. Ross from mml kept blaming my system; bad master cylinder, bad rear calipers [funny, I replaced them all and it had zero impact on the bias issue]. My bias was verified by using an infared temp sensor as well. So, purchased the silvermine rears, problem solved. Funny, I had to actually used the prop valve to tone the rears down a bit-a nice problem to have! I think the silvermine rear rotors are a larger diameter than the other Nissan swaps with I believe yield the desired result [along with larger caliper]. Quote Link to comment Share on other sites More sharing options...
Miles Posted December 19, 2011 Share Posted December 19, 2011 I experienced same issues with mine-modern motorsports 13" front and 240sx rear. Tried many things; more aggressive pads rear, remove stock prop valve & installed wilwood prop valve but no help [even removed wil prop valve-still too much front]. Ross from mml kept blaming my system; bad master cylinder, bad rear calipers [funny, I replaced them all and it had zero impact on the bias issue]. My bias was verified by using an infared temp sensor as well. So, purchased the silvermine rears, problem solved. Funny, I had to actually used the prop valve to tone the rears down a bit-a nice problem to have! I think the silvermine rear rotors are a larger diameter than the other Nissan swaps with I believe yield the desired result [along with larger caliper]. What pads and MC are you using? Quote Link to comment Share on other sites More sharing options...
1 tuff z Posted December 19, 2011 Share Posted December 19, 2011 15/16's master, initially using the pads mml supplied [can't remember the brand now, see their website], then upgraded the rear. Called and spoke at length with engineer at hawk, suggested I start with, at the rear their hps [not enough], then to the hp+ [still not enough] and was tired of spending $100 each time for an experiment. Silvermine rear works, now the only $ I spend are to replace the pads. Rear rotors seem to be holding up very well [3 years now, 4x2 day track events per hear and I see longer sessions as an instructor], on my 2nd set of pads. No regrets with the current setup and wish I had done it sooner. What pads and MC are you using? Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted December 19, 2011 Share Posted December 19, 2011 1 tuff z- Make sure to clue the forum in on the need for bigger wheels with the Silver Mine kit, also, can you address e-brake function with the Silver Mine kit? I think most of us who try to do a "simple disc brake conversion" quickly gain a lot of respect for the engineers who designed the original system. I really appreciate all the time you spent advising me on my brakes. Quote Link to comment Share on other sites More sharing options...
1 tuff z Posted December 19, 2011 Share Posted December 19, 2011 Any brake upgrade has + & - to it. I spent many hours searching / reading information here before I spent my first $ upgrading. Hybridz is a literal treasure trove of information which I like to refer to as my personal z braintrust. RebakahsZ, as you correctly imply nothing is simple. Yes, you may need larger wheels to accomadate larger rotors/calipers and some modifications to allow ebrake functions to work properly. Quote Link to comment Share on other sites More sharing options...
subtle_driver Posted February 16, 2012 Author Share Posted February 16, 2012 ok so not safe to proportion the fronts, and no way to increase the rear pressure if i bypass the stock proportioning valve?? Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.