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Braking Instability?

Edo

Experienced Member
Joined
13 May 2000
Messages
990
Location
Lake oswego, OR
I recently upgraded my Brake's from the stock ssytem to the brembo 13" Setup with the Lotus 4 pot calipers. While this system has monstrous braking capability and ZERO fade, I've noticed that I am having severe stability problems under threshhold braking. The car ducks and weaves and wants to go either left or right all the time. The ABS engagement I used to use as a the limit of how hard I depress the brake pedal, now throws the car to whichever direction of the tire that locks. This is not a small jerk, but a pretty noticeable dive. It was to the point where I was braking hard in the CENTER of the track so I do not get jerked into any of the walls.

My questions is this, how do I get the braking stability BACK into my car? Is it alignment? Tires? Wheels? Brake Bias?? Ride Height? Anyone who has any input PLEASE help me out as this is quite a bit of a problem for me!!
Here are my current settings

Current Tires : Toyo Proxes T1-S
215/35/ZR18 front
275/35/ZR18 rear.
1.5mm Toe OUT front
1.25 degrees Negative camber front
7mm Toe in Rear
2.5 degree's Negative Camber Rear
8.5 Degree's Caster both left and right




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'91 Black/Black #1213
Dali Clutch/Flywheel
Comptech Sway Bars
RM Cold Air Intake
Taitec JGTC Center Exit Exhaust
Comptech SS Brake Lines
Carbotech Panther Plus Pads (Front)
Hawk Blue (HT90) Pads (Rear)
Comptech Harness Bar and Simpson 4 point Harness
Comptech Coilovers with Koni 1 way adjustable shocks
Brembo 12.9" Rotor's with brembo 4 Piston Lotus Caliper
Racing Hart CP-035-R Custom offset wheels
2 piece fully forged and welded (currently the ONLY set in the world)
 
The only thing I can think of here is that the Hawk pads in the rear are biting a little harder than the Panther pads in the front. You may want to talk to Andie Lin at Carbotech (manufacturer of the Panther compound) about this issue. It also seems that your rear toe and camber are aggressive, but it shouldn't cause the car to dart around severly. I have Tarox 6-poiston on the front and rear and when I set the brake bias too far to the rear, the car becoms unstable under braking as you describe. When the bias is fixed, the car behaves normally under braking and I have similar alignment settings as yours.

Good luck and let me know if you have any problems getting ahold of Andie.

DanO
 
Coincidentally, I bought my Brembo kit used off of Andie..

I do know that the Hawk Blue's have alot more initial bite than the Carbotech Panther Plus pads. But my idea was that since the front brake's are significantly more powerful than the rear's it might help to get grippier pads in the rear. This COULD be my problem. I will contact Andie and see about changing out my pads.



[This message has been edited by Edo (edited 29 October 2001).]
 
I could be wrong, but I think what you are experiencing is what I experienced when I had a big brake kit on just the front with small 215 wide front tires. What I found is that, especially at the limit, the brakes will begin locking up the wheels at different limits from left to right. I fixed this by 1. using larger stickier tires (tremendous improvement). I also was able to gain a more linear braking ability by using a kit in the rear that increases braking toque through using a larger rotor (ScienceofSpeed Stage 1 kit).

Tires IMO are your best bet.

I also found the Carbotech Panther Plus to be a very good compound... I think they make them for your calipers.

Cheers,
-- Chris

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SoS_logo.gif

www.ScienceofSpeed.com - Click for more info
www.NSXClassifieds.com - The internet's only exclusive NSX Classified site!
 
I had a similar problem when I got my lotus calipers. some good suggestions have already been made. I changed my front pads to pagid's. the pagid pad may be a little harder compound, because when I changed the problem went away. I am currently using pagid front pads and OEM rear and am quite happy. chris is also probably right about the tires. as mentioned in a previous forum, my old front tires were pretty hard. dano illudes to it, but you could also get a proportioning valve.
 
Originally posted by Edo:
Coincidentally, I bought my Brembo kit used off of Andie..

That's funny. I probably helped Andie take them off his car and I most likely shipped them to you. It's a small NSX world.
smile.gif


I think you're right, replace the hawks and see what happens.

DanO
 
This may be unrelated, but reading your post it sounds like the problem I had with my car after changing fluid. You must have broken the lines to change the calipers and the hard pull to left or right is just the problem I had. The antilock light never came on, and I had a heck of a time until I took it back to the dealer, expecting big trouble.

The whole problem revolved around bleeding the antilock mechanism very well with the special tool the dealer has. Fixed the pulling for me, and it was severe enough I was afraid to drive the car on the freeway as hard or emergency braking sent me into the ditch.

Maybe this is your touble.
 
Interesting...Antilock bleed huh? I remember Chris did this for my car this April, but I havent even touched it since. How often should I do this? I wonder if that could be the problem. OR perhaps I am suffering from sticky ABS Solenoids? I hear that happens if you don't engage the ABS often. (I engage them often, but they could have been stuch before I bought the car)
 
--I also was able to gain a more linear braking ability by using a kit in the rear that increases braking toque through using a larger rotor (ScienceofSpeed Stage 1 kit).--

Chris, if I am suffering from having too much grip in the rear as DanO says, then how would going to a larger rotor help at all? Wouldnt that affect the leverage that the caliper has and thus INCREASE the rear braking? That would make it even WORSE wouldnt it? And also, I didnt see just the rear kit available on your site..Is it available separate from the Front kit?


(BTW as far as Front pads go I am using the Carbotech Panther Plus pads already)
 
Edo,

I suspect this is due to the ABS not capable of doing it job effectively with the big brake it. One of the solution is to run a proportioning valve (which I do).

I would also check the front toe. Most likely u are running an aggressive front toe setup, thus that effect under hard braking.

Or u can start learning threshold braking without using the ABS
wink.gif
 
Is 1.5mm Toe out considered aggressive Toe in the front? I was under the impression that 2mm was factory speck. I dialed it down to try to compensate for this instability problem.

What kind of proportioning valve are you using? How exactly does it work, and how much does it cost?
 
I use 1.8mm toe out.

I guess, u need proportioning valve. I uses Tilton lever type. If I would do it over again, I would use the knob type.

Cost me total around $250 for the lever type. I do my own labor with the help of friend. The knob type will be slightly cheaper.
 
It seems to me, after rereading your post that you are experiencing a directional imbalance. The balancing things discussed would only balance front to rear. Wheel lockup on one side or another would not be affected by this balance, as I understand.

But my car did lock up one of the front wheels, and pull sharply.

I feel it is well worth the effort to bleed them again. I was very reluctant to think my problems were so simple. But they were.
 
Originally posted by nutonsx:
It seems to me, after rereading your post that you are experiencing a directional imbalance. The balancing things discussed would only balance front to rear. Wheel lockup on one side or another would not be affected by this balance, as I understand.

From what I understand, we are talking about a threshold braking situation at the track where just a little bit too much of rear bias will cause significant directional instability. Many of us with big brake kits experience this while adjusting our bias at the track. In this application, under threshold braking, it seems obvious that the rear brake pads (hawk blue) have a cf that is too high for the application. This is logical because the big brakes on the front are allowing the car to stop quicker then before (before the big front brake package), thus transferring more weight off the rear of the car under threshold braking (faster stopping means more weight transfer to the front). Less weight at the rear means less grip for the rear tires and therefore more of a tendency to lock up when threshold braking.

Of course, it's not a bad idea to do a good ABS flush and brake bleed too. But I suspect that changing the rear pad compound to something like a R4s or even the panther plus will fix the problem.

.02
DanO
 
From my understanding, Edo experiencing darting feeling when ABS kicks in. This is due to too effective front brakes and not effective enough ABS. The ABS doesn't prevent locking quick enough, combine with a toe-out, give darting feeling. This is a classic case of darting underbraking on race cars without ABS.

Too much rear brake will give u oversteer under braking. As the rear lockup and the front still maintain traction. This is not darting feeling. This is tail swinging.

I'm not sure how exeprience Edo is in testing cars. From his description, it is certainly not the case of too much rear brakes.

[This message has been edited by Andrie Hartanto (edited 30 October 2001).]
 
Well, both solutions seem relatively simple, so I will try both.

Proportioning valve+new rear pads with less grip.
I'll let you all know how it goes.
BTW Andrie, why use the knob type as opposed to the lever type?
 
Edo,

Don't try both (proportioning valve and new rear pad with less grip) at the same time. U are neating the purpose. The purpose is trying to get less pressure to the front (less front braking) so the ABS can work.

the knob type, u can fine tune, while the lever type has preset positions.
 
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