Zmanco Posted July 16, 2012 Share Posted July 16, 2012 Either brake fluid is fine. What's important is bleeding the brakes (all four wheels) at the very first sign of a soft pedal. Its almost standard practice to bleed the brakes and adjust the rear drums between qualifying and the race in an ITS 240Z with the stock brakes. Seems like a good place to ask what happens to the fluid after if boils and cools? Once it condenses back to a liquid, the pedal doesn't feel the same in my car - it's less firm, at least for the next few days after a track day. Do the properties of the fluid change after a boiling cycle? Perhaps the extreme temp degrades the fluid? Or does some of the fluid that's now a gas dissolve in the remaining liquid and then take a long time to eventually fully return to a liquid state? I know the simple answer is to just bleed the brakes again, but inquiring minds want to know Quote Link to comment Share on other sites More sharing options...
johnc Posted July 16, 2012 Share Posted July 16, 2012 The fluid gets hot enough to outgas. Some of that gas does not condense back into fluid and must be bled off. The outgassing is inside the brake caliper and usually doesn't take a lot of pumping to bleed out. Quote Link to comment Share on other sites More sharing options...
bjhines Posted July 16, 2012 Share Posted July 16, 2012 The last part of this video shows some of the compromises of brake biasing. After I pass the 911 on the downhill straight I have to really toss out the anchor. I know this and I am overly cautious on the downshift because I KNOW!!! that locking up the rears will put me off backwards. I eventually lock the the front inside wheel as I am forced to turn in with WAY TOO MUCH braking left to do. You can see me modulate the pedal to ensure that the front tires get rolling again while I continue to trade braking effort for turn in until I get it sorted. Quote Link to comment Share on other sites More sharing options...
johnc Posted July 16, 2012 Share Posted July 16, 2012 To emphasize... it is far, far more important to have good brake balance/bias then to have ultimate braking power. This is made very clear when you're actually racing wheel to wheel or it starts to rain. Quote Link to comment Share on other sites More sharing options...
johnc Posted July 16, 2012 Share Posted July 16, 2012 iRacing has some good braking videos: Also, check out the technique. Hard on the brakes when you first apply them and then back off. Also note the confidence pump at the end of the long straights and how the gas pedal is squeezed: Quote Link to comment Share on other sites More sharing options...
EF Ian Posted July 17, 2012 Share Posted July 17, 2012 Surely you will be able to get a good brake bias setup if your rear brake setup matches the front setup well. Are the problems with brake bias here not dur to a badly matched setup? Quote Link to comment Share on other sites More sharing options...
bjhines Posted July 17, 2012 Share Posted July 17, 2012 (edited) There is no "matching" set up. The rear wheels have an entirely different set of dynamic conditions. Watch the videos and learn. Edited July 17, 2012 by bjhines Quote Link to comment Share on other sites More sharing options...
240zip Posted July 17, 2012 Share Posted July 17, 2012 Love that heel-toe action. I was watching Jeff Winters in his GT2 240Z while in the car with him at HPR in Colorado. Much quicker shifting action (Jeff), but the braking and heel-toe was similar. Quote Link to comment Share on other sites More sharing options...
johnc Posted July 17, 2012 Share Posted July 17, 2012 Are the problems with brake bias here not dur to a badly matched setup? Generally yes. A lot of folks will put larger front calipers and rotors on their S30 with no change to the back. That immediately increases front bias by a lot. The car feels like its stopping better at the 7/10s that most people drive these cars but at 10/10ths the actual braking distances are longer due to the heavy front bias. Quote Link to comment Share on other sites More sharing options...
EF Ian Posted July 18, 2012 Share Posted July 18, 2012 There is no "matching" set up. The rear wheels have an entirely different set of dynamic conditions. Watch the videos and learn. Of course there is a matching setup, I mean matching as in the rear setup is able to keep up with the fronts so that you can setup the perfect bias. Obviously I don't mean matching as in sticking the exact same setup on the front aswell as the rear, that would be stupid. Quote Link to comment Share on other sites More sharing options...
logr Posted July 18, 2012 Share Posted July 18, 2012 (edited) All it took was one trip around the track with my SR and I knew I wanted/needed better brakes. 12.2 rotors and Superlites all around and I finally have a car that has enough brakes. FWIW, I left the stock proportioning valve and added the new one after the m/c but before the stock valve(Z31 m/c). The adjustment ended up in the middle of it's range. I did it as much for the 5 lug as anything which I am very happy with. It is hard to argue with RPF1's. Edited July 18, 2012 by logr Quote Link to comment Share on other sites More sharing options...
Zinger Posted July 21, 2012 Share Posted July 21, 2012 I'm currently looking into converting the rear drums to rear disc. Even if it's only for looks. I just really hate the drum brakes because their a b*t*h to service. I've seen the maxima brackets and 280 caliper. But seeing as the maxima bracket is hard for me to source, I was wondering what bracket the 240sx calipers use. and what rotor of course. I know all the kits are already together but I'm a college kid. AKA broke. And currently work at Advance auto, meaning I can usually get parts cheap. Just wondering also how much 'modification' was needed for the 240sx calipers as it sounds like the 280z caliper/maxima bracket is pretty much bolt on. Thanks in advance for any help at all. Quote Link to comment Share on other sites More sharing options...
240zip Posted July 21, 2012 Share Posted July 21, 2012 I think the best deal for rear brakes is the $375 kit from this guy in Las Vegas. http://forums.hybridz.org/index.php/topic/102954-desert-z-brake-conversion/ Quote Link to comment Share on other sites More sharing options...
johnc Posted July 21, 2012 Share Posted July 21, 2012 I'm currently looking into converting the rear drums to rear disc. Even if it's only for looks. I just really hate the drum brakes because their a b*t*h to service. I've seen the maxima brackets and 280 caliper. But seeing as the maxima bracket is hard for me to source, I was wondering what bracket the 240sx calipers use. and what rotor of course. I know all the kits are already together but I'm a college kid. AKA broke. And currently work at Advance auto, meaning I can usually get parts cheap. Just wondering also how much 'modification' was needed for the 240sx calipers as it sounds like the 280z caliper/maxima bracket is pretty much bolt on. Thanks in advance for any help at all. Please search the FAQs. There are huge, 10 year old threads that answer your question. Quote Link to comment Share on other sites More sharing options...
Rick Dorion Posted August 18, 2012 Share Posted August 18, 2012 Great topic. In the mid 70's I did time trials at Lime Rock in my 73 240Z which I bought new (sigh). The first outing I had no brakes after the first open practice. I upgraded the pads (don't remeber the brand) and changed the brake fluid to Castrol Dot4. No more fade and the car did well from that point on. For my needs, the stock setup worked. I also had slicks, the usual Bob Sharp acquired springs, koni's and sway bars. Off topic, but I was impressed with the improvement in rigidity from adding a bolt-in 4-point roll bar. Quote Link to comment Share on other sites More sharing options...
letitsnow Posted August 21, 2012 Share Posted August 21, 2012 Those of you that say the stock brakes have good bias, are you using an adjustable proportioning valve or the stock one? Quote Link to comment Share on other sites More sharing options...
johnc Posted August 21, 2012 Share Posted August 21, 2012 Stock for a street car and I've also removed the stock prop valve and added an adjustable one, but only for racing in the rain. For the rear drums its more important to keep them adjusted then which prop valve you have installed. If you take a Unibit and enlarge the existing hole in the face of the drum to about 3/4" and then drill a same sized hole 180 opposite it makes adjusting very easy, without removing a wheel. It can be done in less then 5 minutes and that includes jacking up the back of the car. Quote Link to comment Share on other sites More sharing options...
letitsnow Posted August 22, 2012 Share Posted August 22, 2012 I've been adjusting before autocrosses, but I don't feel like I have enough rear bias. I'm going to get rid of the porterfield pads in the front and go back to a normal compound to try for more rear bias. Quote Link to comment Share on other sites More sharing options...
johnc Posted August 22, 2012 Share Posted August 22, 2012 Have Porterfield make you some rear brake shoes with their R4S compound. Quote Link to comment Share on other sites More sharing options...
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