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? |
jdogg |
Sep 25 2007, 07:17 AM
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#2
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Member Group: Members Posts: 431 Joined: 28-January 03 From: Youngsville, NC Member No.: 204 |
OK...A successful weekend! No cooked calipers, brakes stayed cool and consistent all weekend...1 broken clutch cable cut short Sunday, but an instructor let me try out his SS Camaro....a pig of car, but 380HP makes damn short work of the straightaways....I learned there is very little that is similar between a 3600 LB, 380HP car, and a 2100LB, 140 HP, mid-engine go-kart! Oh, and I fortunately had a spare cable, so Monday was still a go!
BUT I am still experiencing a sinking pedal, and my theory on that is this - in between braking sections, the pads are getting knocked back too far, requiring more pedal travel to get them back into contact with the rotor. I started giving the pedal a pump or two right before braking hard, and that helped immensely, the bute was up high where it needed to be. When the pedal sinks like that, heel and toe is nearly impossible, especially at the threshold...I even knocked the gas pedal loose one time because my foot was so far behind it on the brakes. Is there any way to limit that knock back? Eric, you mentioned removing the knock back pins altogether...would that help and keep the pads closer to the rotor in between braking zones? This is more of a nuisance than anything else, but it would be nice to not have to pump 'em up every time I need 'em. |
stownsen914 |
Sep 25 2007, 09:02 AM
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#3
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Senior Member Group: Members Posts: 913 Joined: 3-October 06 From: Ossining, NY Member No.: 6,985 Region Association: None |
Is there any way to limit that knock back? Are you sure your rotors aren't warped? Also, check your wheel bearings. If they have any slop, the wheel can cock back and forth slightly between braking zones, and knock the pads back in the process. Either problem could occur at the front or the rear, but the front would be more likely, I would think. Good luck! |
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