Hard brake pedal & seemingly no ABS/pump

[forumadmin]

I think the pump, is activiated purely on lack of pressure in the 'pre-charge' system of the ABS. The is a tank which stores ABS fluid under pressure. A pressure switch will sense a low pressure and the pump recharges it. If the pressure is not brought up to normal within 30secs then the warning light will show. Braking hard enough to engage the ABS a couple of times, or even once for a few seconds will get the pump going.

Something I wanted to do is upgrade to the latest ABS unit. I would do that over any repairs to the current system.

[Kaz-kzukNA1]

Kaz - I'd be interested to hear whether much braking is available on an NSX when the servo vacuum goes? I'm paranoid about this since the issue occurred on my student-days volvo 340 (!) and I had no capability to get the pedal down at all. Is the NSX stoppable without the servo do you know?

You can slow down and eventually stop your NSX but it all depends on the conditions.


Unless suddenly something mechanically failed at the booster, you still have the vacuum assist even if you have stalled the engine and thus, you can stop the car in a similar way if you don't panic and try to press the brake pedal multiple times.


If you lost the vacuum completely, then you will need to press the pedal really hard and unless you have experienced it, you won’t understand how hard you need to be.


I’m doing this almost every day but only at the crawling speed like a snail.


In order to get enough space to work on another NSX, I always move my car out of the garage.


I hate starting the engine just for 10sec due to the blowby gas so I normally just push it out.


As my natural habit, I always press on the brake pedal several times before moving the car so I don’t have any vacuum assist when moving the car.


Even at the crawling speed, you must press on the pedal fairly hard.


If I have to do this even at 10mph, I don’t know how quickly I can stop the car….

In a simplified notion, it's the ratio between the diameter of the mater cyl VS the piston at the calliper and thus, you need to generate multiple massive pressure at the master cyl without the vacuum assist.

Kaz

[Kaz-kzukNA1]

The pump was definitely not activating beforehand though. Binding brakes causing the ABS to think the brakes are in use so the pump didn't activate maybe? When I say activate I mean pumping whilst just driving down the road etc not when breaking. Usually I find it pumps after releasing the brake coming out of the driveway.

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Hi, Ed.

Unlike the OEM one, you are using aftermarket opposed piston calliper so the characteristic is quite different from what I wrote in the earlier post. Just ignore it for your case.


I have never dealt with Hi Spec calliper so I don’t know whether it has dust boot or not at the piston.


Like some of the Brembo and other models, you MUST refurbish it more frequently than the OEM ones especially some of them don’t even have the dust boot over the pistons.


Depending on the track condition, dust boot won’t survive due to excessive heat generated so not included in the original design any way.


In UK, I noticed that not just the brake pistons but also the nuts/bolts/etc seemed to get corroded at similar speed/rate to the cars based in coastal area of Japan.


On brake callipers without the dust boot, piston can easily seized if not refurbished regularly with the salt in the air.


The pad at the entry side of the calliper (top side, if the calliper is mounted at the forward section of the disc) has its own self-biting effect so in order to balance the friction level, normally you use smaller piston at the entry side.

Even with this, depending on the conditions, you will get imbalance in pad wear so it is very important to check the status regularly.


It depends on several conditions but you are probably OK to use the same brake fluid for a few track events if you are using the expensive racing brake fluid.

It would be cheaper to use the racing brake fluid than replacing the standard one after every track day if you regularly track your NSX.

This is the good time to check your pads, disc, calliper as you need to bleed both side of the callipers.


If you don’t track a lot, probably better to stay with the standard fluid and replace it after each event and check the components at that time.



Regarding the ABS, it’s pretty much the same as what forumadmin said.


ABS controller monitors the condition of the accumulator pressure switch.


If the pressure at the accumulator drops, the switch will become in OFF status.

With this signal 'AND' the first time when one of the rear wheel speed signal exceeds 10kph (6mph), the ABS pump will kick in.

This is why you don’t hear the ABS pump just after starting the engine but always hear it on leaving your driveway.


It will stop the ABS pump after about 3sec once the pressure switch becomes in ON status.


If the pressure switch doesn’t get ON status (accumulator pressure is still lower than the threshold) within 120sec after the ABS pump was activated, you will get ABS warning light.


If you exercise your ABS first thing in the morning at very low speed before the tyre warms up, the ABS pump will kick in after about 2 – 3 times you exercised it.


If it kicks in every time when you exercised it, you are very likely to have problem with the accumulator or the solenoids.


Any ABS on our NSX before the introduction of the later spec one body solution, it is highly recommended to exercise it regularly at a safe place to prevent debris trapped at the solenoids.


As you didn’t hear the ABS pump for a while, seems like you are holding the good pressure over the long period. This is a good news.


Still, best to flush the system regularly to prevent any issues.

Already saw so many different scenario/failure modes on this type of ABS….


Kaz