Let's Talk Track Brakes |
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Let's Talk Track Brakes |
jdogg |
Aug 10 2007, 08:09 AM
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#1
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Member Group: Members Posts: 431 Joined: 28-January 03 From: Youngsville, NC Member No.: 204 |
OK, so I've had my car for almost 6 years now, and it has been through a LOT of changes over those years...It started as a stock class 2.0 AXer, then to street prepared, the to SM2 with the addition of the -6. I had done a smattering of track events over those years, primarily focusing on AX, but last fall the track bug bit and bit hard!! I've done about 8 of 'em since October last year, and just can't get enough.
But this brings me to my question(s)/issues. As my driving is improving, I find I am being much harder on the car (a good thing), but some issues are coming to light, most notably the brakes. I have the much hyped 914club billet hubs on my car, utilizing M calipers, SC vented (not cross drilled) rotors, Carbotech XP10 racing pads, brand new 19mm MC, etc. The brakes work very well...once the pads get some heat in them they will stick your eyeballs to the windshield with no fade issues. The issue I am having with this set up is the pedal softening and the travel growing after a couple sessions. At first I suspected the MC, so I replaced it...then after bleeding the system and leaving it under pressure with my power bleeder, I noticed some fluid seepage around the RF caliper. The calipers were rebuilt last fall and have about 8 track weekends on them, but I went and got a new rebuild kit and rebuilt it. I thought that maybe that was a potential source of air and a possible reason for the pedal travel issues. I spent the past weekend at Carolina Motorsports Park (CMP) in lovely east bumfuck middle of nowhere no cell service one stoplight Kershaw, SC. A very challenging layout, tight and technical, and very hard on equipment with a lot of hard braking zones, so I figured it was the perfect venue to test out my brand new MC and freshly rebuilt caliper and see if I could keep a pedal all day long. After session 2 on Saturday the pedal travel had indeed moved again. So I bled the brakes (heel and toe with a low brake pedal is nearly impossible) and the pedal came right back where it needed to be. I resigned myself to the fact that I was just going to have to bleed 'em every two sessions. Well, it was successful, uneventful rest of the weekend with plenty of bleeding (although it was hot, really fucking hot...103 on Sunday with lots of humidity). Fast forward to Monday night when I go to unload the car from the trailer....no brakes!!! WTF?!?! Seem I have blown the left front caliper out now too, and this one leaked fluid all over the damn place.... So does everyone need to bleed their brakes that often to keep a firm - high pedal? Is rebuilding calipers every 2 or 3 events whether they need it or not going to need to become a regular maintenance item? Is there a better way? |
Eddie914 |
Sep 1 2007, 11:57 PM
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#2
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Unregistered |
Are you overheating the front brakes or the rear brakes?
My 914-6 3.2 is set up with 911 SC brakes, Porterfield R4 pads, ATE Superblue fluid and a manual proportioning valve in place of the stock proportioning valve. Many on the board indicated that the stock proportioning valve can be eliminated. With the manual proportioning valve set wide open, rear lock-up was quite easy to invoke. I continued to increase the brake bias to the front until rear lock-up was eliminated then added an additional turn to the adjustment knob for a safety margin. The last couple of events the pedal has softened during the day. When the front brakes were bled, the soft pedal continued. When the REAR brakes were bled the nice hard pedal returned???? What gives? Don't the front brakes always overheat first? At the last event I used an infrared heat gun (I know ... it's not the best type of instrument to measure temperatures on shiny metal) to compare the front and rear brake temperatures after a track session (followed by a cool down lap). Guess what? The rear brakes were MUCH hotter than the front brakes! 550 degress versus 275 degrees. The front brake cooling ducts must be working pretty well. Now it's time to fabricate rear cooling ducts. Anyone have any ideas for rear ducting? Eddie |
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