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Help needed with '92 brake system O_o

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Hi to everyone.
Sorry in advance for my english but I'm italian and therefore not so good at it...

I need help from whoever might have previously experienced a similar problem or might have useful suggestions on how to solve it. The facts:

My '92 NSX still has stock brakes. I went to the track with her 3 weeks ago for the first time, and had a 25 mins. round. After it, I let the brakes and motor get cooler before stopping the engine.
I had old brake pads on the car, and consider I use it once a week or less (I have another car for daily commuter). That's why I thought the "braking feel" on the track was horrible (not good as it was 6 years ago when I bought it, at least).
When I stopped, I noticed the rims were full of brake powder, and that the original rims were slighly "cooked" --> their silver had a little "brown" color.

But...the real problem started now: after 15 minutes that the car was parked and the engine stopped, I tried to push the brake pedal and it went all way to the ground without resistance. Therefore I decided to let the brakes have some extra cooling by going around at slow speed for some minutes. This seemed me to solve partly the problem, and when I decided to head back home, I drove slowly because the braking strenght was more than halved.
Furthermore, the rear left brake pad was "squeaking" like if it was a little braked.
When I brough the car to my mechanic, he told me that the rear pads were completely worn, and just a replacement maybe would have cured the problem. That was not the case, as the rear left brake was still a little "braked" (and the front right a little, too).
As I have an additional security system on the car which acts on the brakes (it slowly applies pressure to the circuit, braking more and more until a complete stop if not disabled, and it is mechanic, non electronic), we thought the problem might have arised due to it and removed the brake line to which it connected, exchanging it with a straight, original brake line.
No way... and the strange is... now the "braked" wheel is the rear RIGHT instead of the left !!

The calipers open when pushed, so they aren't blocked or clogged by brake dust. The security system is excluded. The lines have already been bleed many times (at least once every trial).

HELP !!! Should I have to think something with the ABS pump is broken ?

ANY feedback, experience, idea is welcome !!

...and thanks in advance to everyone willing to help.

Cristiano from Italy.
 
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Cristiano,

First of all your English is very good:). Your problem exists because you probably have older brake fluid, and maybe even DOT3 type instead of DOT4 type in the system. You will want to do a complete flush and use better fluid like Motul, ATE Blue, or similar.

Brake fluid will take on water over time and lower the boiling temperature, so it must be changed, especially for track use.

The reason the pedal got worse when you stopped is called "heat soak", the brakes actually got hotter when you stopped and boiled the fluid:).

Good Luck,
HTH,
LarryB
 
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Larry Bastanza said:
...Your problem exists because you probably have older brake fluid, and maybe even DOT3 type instead of DOT4 type in the system.You will want to do a complete flush and use better fluid like Motul, ATE Blue, or similar.
The reason the pedal got worse when you stopped is called "heat soak", the brakes actually got hotter when you stopped and boiled the fluid:).

Many thanks for your quick answer and advice, Larry, but the brake lines were flushed and new Castrol DOT4 fluid was inside when I went to the track.
Then, we replaced it again with new fluid when we changed the rear pads after I came back home. And the problem is still there. The strange phenomenon is that one or two calipers are a little "braked" when we try the car. And not always the same (rear left, then rear right).

Any more ideas ? I don't know where to check for problems...maybe some old rubber pieces detached from inside the lines and obstruct somewhere at random ??
 
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mm......


OK, Tell me about your brake pad choice, and also please let me know about your driver skill level. Novice, Intermediate, Advanced, Pro level?

It seems to me they are overheating for sure, but I will say I am surprised that Castrol DOT4 is cooking:). When you say one or two calipers are "Braked" do you mean they are "dragging" like your foot is on the brake pedal slightly??

Also you mentioned the rear specifically. Many NSX's I service that are used alot on the track need rear brake caliper maintenance often. The stock caliper floats on pins that have high temp grease to slide on, and it bakes hard as steel and the caliper can freeze, or get loose and kind of bang around. My very experienced track guys get the "rear caliper" grease fix about every 2-3 pad changes, sometimes more then once a track season. It may be why your caliper is "braking" always. Also please check your emergency brake system to be sure the e-brake is not dragging slightly, this gets worse as things heat up.

HTH,
LarryB
 
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Larry Bastanza said:
OK, Tell me about your brake pad choice, and also please let me know about your driver skill level. Novice, Intermediate, Advanced, Pro level?
When you say one or two calipers are "Braked" do you mean they are "dragging" like your foot is on the brake pedal slightly??
LarryB

Hi again Larry, and thanks again for the suggestions.
I immediately phoned my mechanic and told him what you suggested: if he has time this weekend he'll check what you said.

As for the pad choice...ORIGINALS.
As for the driver level...NOVICE (I went to the track only 3-4 times, but they say I am not so bad at all...lots of PSX GT3-4 training :)). My daily driver is a FR Renault Clio 2.0 RS, a completely different style of driving, and of braking.
As for the "braked", well, yes, I mean exactly what you described.

As soon as the car will be checked I'll write back here and report...
MANY THANKS TO DAVE'S SUGGESTION, TOO !

Cristiano.
 
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