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Reducing front brake bias

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  • Here were my steps:
    1. "Bench Bleed" BMC on vehicle
      Quick video here
      I did this because the system has been dry for months. The gurgling sound was a little weird. After this I removed the black hose and installed the brake lines as fast as possible, torqued fittings without any bleeding at the conenction.
    2. Fluid fill through lines
      In order of bleeding calipers (rear driver, rear pass, front pass, front driver) I cracked each bleeder loose and slowly pumped the brake pedal to fill the lines. A hose & bottle was hooked to the bleeder with enough fluid in the bottle to prevent air re-entry. In retrospect I don't know if this was correct.
    3. Regular 4 corner bleed
      In the same order as above I bled the calipers - catch bottle hose attached to bleeder, friend pumped 3 times and held, I opened for a few seconds then shut. Friend releases pedal and repeats. I did get it to the point where no air was coming out.


    I may grab some hardlines from the auto store to make better BMC bench bleeders. I'm not sure what else to do other than repeat this. I may need to prime that valve I showed a few posts ago but I'm not certain, FSM seems to avoid talking about prop valves.

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    • I'd start with DTC-70's since you don't really know what piston size caiiper you have in front. The helical diff already makes the car eager on turn in also. You can get away with more rear bias with a 1.5 or 2 way.

      Just bleed the crap out of the system. If you continue to have a soft pedal, your BMC might need to be rebuilt. If it was left dry for too long and exposed, you may have scored the bore.

      I've taken out that prop valve to pull shims (old car) and put it back in without rebleeding without getting a soft pedal. Although, that's the spring style prop valve. YMMV
      Core4 Motorsports
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      • I bazooka'd it the other night - primed the valve unit, properly submerged the bench bleed lines and rebled each corner. Pedal was still almost non existent then I adjusted the pedal pushrod at the pedal jam not. They engage!

        It's 2am here and I just finished my check out drive, I think it's feeling good. Car hasn't been out in a while so I'm just gonna have fun with it at the track. Thanks all for the help.

        PS - I feel like I may have seen a flash or two by the window after braking, maybe a spark. Is any of that normal? Brand new dtc-60s front 30s rear.

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        • Yeah dtc60s shoot sparks in the dark.

          Comment


          • Originally posted by enerj View Post
            I bazooka'd it the other night - primed the valve unit, properly submerged the bench bleed lines and rebled each corner. Pedal was still almost non existent then I adjusted the pedal pushrod at the pedal jam not. They engage!

            It's 2am here and I just finished my check out drive, I think it's feeling good. Car hasn't been out in a while so I'm just gonna have fun with it at the track. Thanks all for the help.

            PS - I feel like I may have seen a flash or two by the window after braking, maybe a spark. Is any of that normal? Brand new dtc-60s front 30s rear.

            How'd it go?

            And I thought you already had DTC-60's for the rear Z32's? Which I realize now, I didn't think they make because I wanted to try DTC-60 front and rear before and couldn't find them at the time. I ended up going HT-10 in the rear then.
            Core4 Motorsports
            CLICK HERE for Wilwood FSL6R Radial Bracket & Rear Wilwood BBK GROUP BUY
            S14 VQ AER Endurance Racing Team

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            • Track day was a success - nothing broke, engine ran great, no brake shimmy when hot which has been my issue to date. I was on DTC-30s in the back and 60s in the front.
              The braking felt pretty even, I didn't notice the front or rear locking up before the other. Car is non-abs so I usually feel it in 1 wheel first, but if felt pretty good.

              There was 1 strange issue where the rears would squeal pretty loud a few turns in, particularly during hard braking turns chained together. It kind of felt like the braking got stiffer and less powerful.

              It makes me wonder about my rotor & bedding quality, I'm always on new rotors since I'm usually trying to fix the brakes. I get serious envy for these mirror surface rotors even though I don't think that's ideal either. Mine seem to get light scratches and non-uniform looking 'rings', almost like they haven't bedded completely? These pics are after the drive home, they looked a little more raw at the end of the track day.

              PS - I don't wanna hijack this thread, I'll try to start a new one soon. If I can get some free time and some pressure readouts (guys at work mentioned gauges that go in the bleed port), I'll try to get some readings with/without the enclosed prop valve.
              Attached Files

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              • You're probably slightly overtemping the rear DTC-30's. Take off the dust shields for your Z32 rotors, as those choke down flow to the cooling vanes, and you don't tend to get good cooling to them anyway since the airflow has to take a sharp 90 degree turn into the vanes. A small duct/scoop can help cool things down if they're still hot.

                My rear DTC-30s were really loud when they were up to temp BTW, so they do make noise. But just judging from the hue of the rotor, looks like they were running hot on the outer edge.
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                • The concentric ring pattern is normal. It may get more uniform the longer you run the car at the track.

                  But, yea, it looks like the rears are being slightly over worked, which isn't surprising to me. It's the reason I went from DTC-30's in the rear to HT-10's on my S13. I got pad depositing/smearing in every race that I ran DTC-30's.

                  I never did try to duct them or deflect airflow to them though. Dust shields were gone.

                  Extended periods of cold driving on race pads will clean your rotors off so depending on how long your drive home was, that should be taken into consideration.
                  Core4 Motorsports
                  CLICK HERE for Wilwood FSL6R Radial Bracket & Rear Wilwood BBK GROUP BUY
                  S14 VQ AER Endurance Racing Team

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                  • Thanks for the input guys, I'll give the HT-10s a try. I don't want to check how much I've spent on pads for this freaking car...

                    I'd still like to do the math on piston sizing, I expected it to be front bias with the big Stoptech kit. Would a stock prop valve delete + adding an aftermarket one help dialing back the rear? I'm still in favor of the pad change for the next track day.

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