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a2low240
12-19-2005, 12:52 PM
Has anyone had any problems with knockback on the S13's due to weak wheel bearings? ( Little or no brakes after hard turns )
If you are unfamiliar with this here's the link.
http://www.stoptech.com/tech_info/wp_knockback.shtml

Thanks for any insight.

'97 S14 SE Turbo
12-19-2005, 01:37 PM
Not on S13, but on my S14 with Z32, I've noticed similar situations such that made it a habit for me to quickly jab the brake pedal prior to braking zone. Sometimes it's brake fluid issues, heat, but iirc couple of times, it may be this situation. I would think it's a bigger issue with fix/single piece hat/disk where floating hat/disk arrangements have a bit more "slack".

gunluvS14
12-19-2005, 02:19 PM
Tap-up the brakes when necessary

This practice may not sound glamorous, but you might be surprised to find how many professional road racers use this technique on a regular basis. All that is usually necessary is a one- or two-tap application of the brake pedal just moments before your braking zone arrives. It takes some practice to get used to, but like heel-toe downshifting eventually it just becomes habit. Note that if you are applying the brakes hard enough to feel the car decelerate you are applying too much pressure you only need enough pressure to seat the components, not to build torque!



now I know why they do it, I saw so many onboard videos where they tap the brakes before braking deep. cool, learned something today

_Def_
12-19-2005, 05:44 PM
No knockback on my S13 with Z32 brakes. I have GTO front 5 lug hubs.

'97 S14 SE Turbo
12-19-2005, 10:27 PM
Do you run the full Z32 brake pad shims and clips? And what pads. (Just want to see if anything else makes a difference.)

In my situation, with OEM front bearings, I run full brake pad shims and clips and have slight issues. This is on the Aluminum Z32TT calipers with Powerslot rotors. I run Metal Matrix street pads so some of the time, I'm fighting fade.

RDM_II
12-19-2005, 10:41 PM
I've only felt that type of action (could have been fade, I thought it was) once, my first time out at Road Atlanta and on my very last run of the day. The brakes were cooked by that point anyway, but it was only at the end of the back straight before the chicane that I noticed it, this was on full Z32 brakes, OE master cylinder, no shims/clips, and Axxis MM pads. The pedal dropped considerably on the second lap, enough to get me downshifting to 3rd and pointed towards the gravel trap just in case. I guess there's no real way to since the brakes were last used (hard) going into turn 7, and could have been floating as mentioned in the article.

_Def_
12-19-2005, 11:01 PM
Do you run the full Z32 brake pad shims and clips? And what pads. (Just want to see if anything else makes a difference.)

In my situation, with OEM front bearings, I run full brake pad shims and clips and have slight issues. This is on the Aluminum Z32TT calipers with Powerslot rotors. I run Metal Matrix street pads so some of the time, I'm fighting fade.



Full factory clips and shims on 30mm Al calipers with "Brembo" blank rotors that are now surface cracked into oblivion.

Matrix street pads on the track is downright scary. I faded Carbotech Panther Plus pads my last two times out trying to crack into the mid 1:40's at Road Atlanta on street tires so I need to step up to a full on track pad like Hawk HT-10's. I hear they're a biatch to modulate on street tires, but I need 1650*F fade temps baby...

_Def_
12-19-2005, 11:05 PM
I've only felt that type of action (could have been fade, I thought it was) once, my first time out at Road Atlanta and on my very last run of the day. The brakes were cooked by that point anyway, but it was only at the end of the back straight before the chicane that I noticed it, this was on full Z32 brakes, OE master cylinder, no shims/clips, and Axxis MM pads. The pedal dropped considerably on the second lap, enough to get me downshifting to 3rd and pointed towards the gravel trap just in case. I guess there's no real way to since the brakes were last used (hard) going into turn 7, and could have been floating as mentioned in the article.



If the pedal really dropped AND you noticed the pads not providing friction then you likely boiled a bit of your brake fluid while fading your pads. I boiled some Prestone DOT4(which is *NOT* DOT4) in 2 laps in my 240SX due to running out of Ate Superblue the night before a track event while bleeding brakes. The pedal felt a bit spongy half way through my first hot lap then going into T10a I had that sucker to the floor pumping like a madman. It was an easy way to slightly change the weight distribution of the car down a few microns by crapping my pants since I was on the SR's speed limiter when this happened.


Man... I haven't been on the track in a long ass time, I really need to get back out there.

SoSideways
12-19-2005, 11:05 PM
Well, the article suggests that "knockback" only happens AFTER a serious cornering load, or a series of serious cornering loads were applied on the brakes.

Russ, you said that you used the brakes hard going into turn 7, but the deflection could have happened right after you let off the pedal, and just kept deflecting until you applied the brakes for the chicane after the back straight.

Perhaps in your situation, since you said the brakes were cooked, the perhaps, under extreme heat, the OE components suffer more deflection than when they're at normal temps that the hardware will see on the streets?

'97 S14 SE Turbo
12-20-2005, 03:16 AM
Matrix street pads on the track is downright scary. I faded Carbotech Panther Plus pads my last two times out trying to crack into the mid 1:40's at Road Atlanta on street tires so I need to step up to a full on track pad like Hawk HT-10's. I hear they're a biatch to modulate on street tires, but I need 1650*F fade temps baby...



They work alright for shorter tracks <1.6 miles. Burnt up a set on a long 3.2 mile track, and the only time where I really faded the brakes. I believe it's also how I apply them. I'm a late brake type and I jab hard and get off the brakes as soon as possible. Habit gained from tracking with stock S14 brakes and Axxis MM pads.

a2low240
12-20-2005, 08:08 AM
The track that we were running was at Summit Point WV and we were loosing almost all the brakes after the lower part of the track, the problem also was discovered at Watkins Glen. I think it's time for wheel bearings, anthough the wheel does'nt visual move it's worth a shot for better brakes.

The car in question has Stoptech 4 piston brake kit, Z32 rears and z32 master cylinder. I'm thinking with the bigger the rotor the bigger the problem with knockback.

asad
12-20-2005, 09:08 AM
I'm thinking with the bigger the rotor the bigger the problem with knockback.



Yep, Stoptech even writes in the linked article that rotor size is linearly related to the magnitude of the knockback problem.

Asad

RDM_II
12-20-2005, 10:03 AM
Well, the article suggests that "knockback" only happens AFTER a serious cornering load, or a series of serious cornering loads were applied on the brakes.

Russ, you said that you used the brakes hard going into turn 7, but the deflection could have happened right after you let off the pedal, and just kept deflecting until you applied the brakes for the chicane after the back straight.

Perhaps in your situation, since you said the brakes were cooked, the perhaps, under extreme heat, the OE components suffer more deflection than when they're at normal temps that the hardware will see on the streets?



That sounds plausible. Turn 7 is a very tight right hander and going into you're on the brakes hard to scrub off speed since turn 6 really isn't very tight and you've just come out of a short straight where you've tried to pass a car or two so there's a tremendous amount of entry speed. I've lost the backend before trying to get the car slowed enough to take it on the right line entering the turn, so the braking combined with thr extreme cornering Gs would easily cause knockback. After that it's a full throttle up to 120+ until the next braking zone. I guess next time I'll pay more attention to pedal feel to know for sure.