69sroadster Posted June 5, 2012 Share Posted June 5, 2012 So over memorial day weekend I took my zx for the first time to a "real race track" at Hallet with my family camping there over night. After about 5 minutes into the second HST session my brakes seemed to disappear going into the near 180 degree turn. After a brief panicky feeling and pumping the brakes, they came back enough to slow down in time for a deeper than normal apex (not in the grass). I've bled them and found no air, but a little chunk of blackish hard crud came out of the left rear bleeder. I thought that was wierd. I also bled the master cylinder first, again no air. I also found no fluid leaks anywhere. The pedal initially seems low but pumps up quickly and holds. It also seemed that the rear brakes appeared to be abnormally worn than previous to the racing....excuse me high speed touring...and more than the fronts. After reading a good lexus master cylinder 101 write up I think that the front circuit of the master cylinder is failing or has failed. I've ordered a wilwood 1" for now as I'll be upgrading the brakes eventually to a larger set. I've also looked into the front resevior again after a few days of local limping to/from work at slow speeds to confirm that the fluid is still not leaking out. No leaks noticed, level was the same but I did notice how much more dirty the fluid there looked than the crystal clear it was after I flushed just prior to the racing. My bet is that the original seals in that original master cylinder broke down under the high temp fluid and hard braking from 100+ mph speeds. Has anyone else seen something similar to this? Also, for those who have done the AZC big brake kits to the ZX and track their car...has it held up to your expectations over time? I've seen writeups with initial great reviews but haven't seen a long term feedback on them for a ZX yet. Sam Kraemer Quote Link to comment Share on other sites More sharing options...
2eighTZ4me Posted June 5, 2012 Share Posted June 5, 2012 First off - what brake fluid are you using? Some of the symptoms sound like brake fade. What pads are you running? What happens when you pump the pedal and hold it? Does it slowly make its' way back to the floor? The brake system is a sealed system - so any dirt/debris you see either got accidentally dropped in the master somehow, the seals are coming apart, or you got water in the system in the form of condensation that is rusting the bores of the calipers. Brake fluid attracts water, and with a lot of hot/cold/hot/cold on the track, condensation can potentially build up. I'm no expert - others please chime in - just my opinion..... When you say 'disappear' - did the pedal go to the floor, or was it firm and you just plain weren't stopping? Quote Link to comment Share on other sites More sharing options...
johnc Posted June 5, 2012 Share Posted June 5, 2012 Very common problem. You probably overheated the pads and/or fluid. There is air in the lines, you just need to bleed a lot more. And read up in the Brakes FAQ before spending any more money on brake parts. I can't think of a situation where you would need a 1" MC on any of these cars. Quote Link to comment Share on other sites More sharing options...
69sroadster Posted June 6, 2012 Author Share Posted June 6, 2012 I was running wilwood 570 BF and porterfield r4s pads all around. I have read through the brake faq and saw consistent negative feedback with rebuilt BMC's to replace the ZX unit. I will flush the system, again with 570, once the 1" wilwood comes in. If that ends up being overkill like you mention, then I'll figure out the best place to get a rebuilt ZX unit and swap it back on instead of the wilwood 1". That just seemed like a cheap alternative that should provide more juice if/when I ever do swap to the big brake kit. When this happened I thought at first it was just a hard pedal but then realized it was all the way down. I pumped and it came back up along with the braking response. It's still like this now, but like I said I have not been able to find any source of brake fluid leak and still haven't seen the fluid level drop in either bowl. I need to get another pedal pusher to confirm the fronts aren't doing what they should while I try to rotate a tire up front. I was also running soft hankook ventus DOT slicks at the time...245/40/17's. Boy did I love those around the turns versus the old nitto nt05's. Quote Link to comment Share on other sites More sharing options...
69sroadster Posted June 21, 2012 Author Share Posted June 21, 2012 I've re-bled the MC on a bench, and in the car, and the rear and front calipers....not much difference really. I've checked the vacuum booster reaction disk (okay) and MC adjustment rod. There are no leaks. The only thing I can think that is still going on is either the brake calipers are having issues...ie not self-adjusting or something like that. Quote Link to comment Share on other sites More sharing options...
69sroadster Posted December 21, 2012 Author Share Posted December 21, 2012 just an update to how this finally panned out. the first problem i discovered earlier on was that the left front caliper was literally seized with a little bit of brake application still on the rotor. I replaced the caliper and still had some wierd issues as described above. I checked everything again and after a bit of driving noticed some wierd wearing marks on the left front disc. I pulled it off again and noticed that the left front caliper floating pins had an issue for the caliper to ride on. The upper/forward pin was also seized. I could not for the life of me get it to free up so I found a replacement one at the local yard cleaned it up and greased it appropriately. Magically the brakes still feel firm, but at the correct height and have much better feel and stopping power. I chalk it all up to the old and not serviced well caliper and mounting bracket/floating pins. Quote Link to comment Share on other sites More sharing options...
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