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? |
Eric_Shea |
Aug 13 2007, 09:24 AM
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#2
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PMB Performance Group: Admin Posts: 19,275 Joined: 3-September 03 From: Salt Lake City, UT Member No.: 1,110 Region Association: Rocky Mountains |
Late model M-Caliper pistons (kinda harder to find in M-Calipers but some had them) or A-Caliper pistons. Yup, they're the same size.
Knock-back pins are the ones that slide into the pistons. By 76 or 77 (I think) ATE had done away with them and went with the later dish or cup style pistons in the same calipers. Knock-back pins are meant to literally knock the pad back toward the rotor offering a high pedal feel. They have been known to be problematic in race cars and many simply remove them or their recepticals. If you stay with your current pistons and you're racing, you may want to simply remove the mechanism inside the piston (C clip and yank). If you go with the later cup pistons simply snap the pins off with a pair of needle nose pliers. One thing I've noticed that hasn't been touched on is the rubbing issue. This is a "Bozo No-No" That's what is cooking your calipers. No, a standard brake lathe will not do it, they're meant to do the sides not the edges. You should find a machine shop with a large enough lathe and mill about 2mm off for clearance. I would also have the rotor cryo'd before or after that so you're not always milling rotors. Do that... get some ducting in there and you'll be a happy |
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