Need some help diagnosing a "clunk" under braking.
08-30-2010, 06:46 PM
#76
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Jim, I would but I go to the track as well and changing the pads frequently gets expensive. I have NEVER run them on my CAB, GT3, or the Turbo and this is the first time I have ever heard this sound.
08-30-2010, 08:13 PM
#77
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JR's point is a good one. I'd check the tops of those X74 struts and make sure that the nuts aren't loose. I had a friend who's 996 C2 was clunking under track duress and the strut top bolts were loose... so loose in fact, that the holes had some grooving in them from all the movement.
Another thought. Are you running the flat spring that holds the pads in place? I know you're not running the spiders, but perhaps your flat spring is old and doesn't apply enough pressure to the tops of the pads to keep them settled under hard maneuvers. If you're not running the flat spring, then maybe you should throw one in and see if that fixes the noise.
If none of this works and you've already ruled out most of the common suspects, the ONLY fix is to keep the brake setup and replace the entire rest of the car with a 996-3.
Problem solved.
Another thought. Are you running the flat spring that holds the pads in place? I know you're not running the spiders, but perhaps your flat spring is old and doesn't apply enough pressure to the tops of the pads to keep them settled under hard maneuvers. If you're not running the flat spring, then maybe you should throw one in and see if that fixes the noise.
If none of this works and you've already ruled out most of the common suspects, the ONLY fix is to keep the brake setup and replace the entire rest of the car with a 996-3.
Problem solved.
08-30-2010, 08:41 PM
#78
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Spring clip are new and in place. The only thing I haven't checked is the strut top bolts like JR suggested. The car goes up on the lift this weekend after we get done prepping Scott's car for the track. I'll have a serious look then. I'd like to have this figured out by the end of the weekend so I have the ability to get it out of the back of my mind BEFORE I come barreling down to T1 at a healthy clip praying the brakes do their job 
08-31-2010, 12:00 AM
#79
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Spring clip are new and in place. The only thing I haven't checked is the strut top bolts like JR suggested. The car goes up on the lift this weekend after we get done prepping Scott's car for the track. I'll have a serious look then. I'd like to have this figured out by the end of the weekend so I have the ability to get it out of the back of my mind BEFORE I come barreling down to T1 at a healthy clip praying the brakes do their job
08-31-2010, 12:15 AM
#80
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Dude, there's plenty of runoff in T1... 
On a more serious note, your first post notes the noise at low speed just before coming to a stop. Later posts note the noise at high speeds under heavy braking, possibly coming from both sides.
Do you ever hear the noise when you're NOT on the brakes? I bet it's the pads... especially since you double checked everything else (including the wheel carrier and caliper bolts) and I know your attention to detail.
Did you use new longer caliper bolts?
PN 999 067 050 09 (M12x1,5x77) "TURBO" versus
PN 999 067 047 09 (M12x1,5x85) "TURBO M450, GT-2, 996 GT-3"
Check the strut tops, check the inside of your wheels for any funny business marks, & mark the nuts on the ARBs just for sh*ts and grins. What about the front diff? Any drips?
I'm still thinking it's pad knock...
On a more serious note, your first post notes the noise at low speed just before coming to a stop. Later posts note the noise at high speeds under heavy braking, possibly coming from both sides.
Do you ever hear the noise when you're NOT on the brakes? I bet it's the pads... especially since you double checked everything else (including the wheel carrier and caliper bolts) and I know your attention to detail.
Did you use new longer caliper bolts?
PN 999 067 050 09 (M12x1,5x77) "TURBO" versus
PN 999 067 047 09 (M12x1,5x85) "TURBO M450, GT-2, 996 GT-3"
Check the strut tops, check the inside of your wheels for any funny business marks, & mark the nuts on the ARBs just for sh*ts and grins. What about the front diff? Any drips?
I'm still thinking it's pad knock...
08-31-2010, 11:01 AM
#81
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I'm almost positive it's pad knock but I just have never heard pad knock like THIS before. I have the proper caliper bolts and have checked everything several times over. This afternoon when I get home from campus I am going to check the strut top bolt like JR suggested and mark all the bolts.
I have a warranty service appt this week for replace the third brake light so if I haven't figured it out by then I'll have another set of eyes (Porsche tech) look into it.
I have a warranty service appt this week for replace the third brake light so if I haven't figured it out by then I'll have another set of eyes (Porsche tech) look into it.
08-31-2010, 11:13 AM
#82
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^why don't u go brake as hard as u can 50 times from 100-20 whatever is loose will literally snap off- suspension or brakes- u may need to get it towed to dealer though. Just a thought. Mike
08-31-2010, 03:54 PM
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08-31-2010, 04:09 PM
#88
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Alright, so just checked and here is what I have. The 3 nuts that hold the 3 strut top bolts in place are nice and tight. The one in the middle I can't get to to figure out if it is tight. By hand it feels fine though. See the picture attached to see what I am talking about. There is no way for my to get a wrench in that opening.
