Brake Fluid Leak at Bottom of ABS

[Heineken]

Well, looks like another busy weekend

PS: Finding the descriptions should be no problem, I remember at least one PDF for a rebuild and several videos on how to flush it manually.

[britlude]

the ABS system is completely separate from the rest of the braking system, save for 4 pistons controlled by the solenoids.... that's why the ABS system fluid can be completely drained without affecting the main brake fluid reservoir.....

[goldnsx]

the ABS system si completely separate from the rest of the brakingg system, save for 4 pistons controlled by the solenoids.... that's why the ABS system fluid can be completely drained without affecting the main brake fluid reservoir.....

That's interesting as I've my newer pump since 10 years now and completely forgot how the old pump works. Problem is that I know of an NSX where the brake pedal is ultra long (not safe!) and the ALB reservoir is empty. I correlated the long pedal to this but now I'm not sure where to start. It's not my car...just trying to help out.

[Heineken]

If I understood the technical description correctly than the wheel pressure control is realized by two separate fluid systems:

1. The ABS system
2. The master cylinder and caliper system

Both systems are interconnected via a sliding piston, effectively separating both fluids but allows the ABS system to manipulate the master cylinder / caliper pressure



If high pressure from the accumulator is pushed into chamber C (by opening the inlet valve an closing the outlet valve) the sliding piston is pushed upwards and:

• disconnects the master cylinder from the caliper
• enlarges chamber B which causes the caliper pressure to drop
• reduces chamber A which pushes back the pedal

The volume pushed back into the master cylinder (via chamber A) matches the volume by which the chamber B was enlarged. As a result, the brake pedal is pushed back to a position that matches the lower pressure of the caliper.

When the wheel stops locking the inlet valve is closed and the outlet valve opened. Chamber C is then connected to the pressureless reservoir and quickly discharges that way, supported by the master cylinder pressure in chamber A. Once the sliding valve hits bottom, the master cylinder and the caliper are once again connected. Pressure at the caliper can then be increased the usual way (by further depressing the brake pedal).

Let's hope that description makes sense and not only to me

[goldnsx]

BTW what happened to the German forum?

[Heineken]

BTW what happened to the German forum?

The one I joined was never much of a help to me, to be honest. The things I posted (like how to repair broken plastics, capacitor replacement, Tokyo Motor Show) weren't taken up in any useful way (except from a friend). It's basically a three-to-four man show and some of them are seriously difficult to discuss with ..

[goldnsx]

The one I joined was never much of a help to me, to be honest. The things I posted (like how to repair broken plastics, capacitor replacement, Tokyo Motor Show) weren't taken up in any useful way (except from a friend). It's basically a three-to-four man show and some of them are seriously difficult to discuss with ..

Same experiences for me with that forum. Plus two "wannabe part dealers" with quite a strange behaviour (I've read the story about the headlights...). This forum here is much more technical. So you're in good hands here.

Thanks for the description of the ALB system. According to the image of the system I'm wondering what happens if the piston in the ALB is faulty and lets air from an empty ALB system into the main brake system ->long pedal stroke. On the other hand the master brake cylinder is leaking (sweating) which has to be addressed. The car has been sitting for more than 10 years...yet the owner has still to decide to wake it up.

[Heineken]

Same experiences for me with that forum. Plus two "wannabe part dealers" with quite a strange behaviour (I've read the story about the headlights...). This forum here is much more technical. So you're in good hands here.

That's good to hear

Thanks for the description of the ALB system. According to the image of the system I'm wondering what happens if the piston in the ALB is faulty and lets air from an empty ALB system into the main brake system ->long pedal stroke. On the other hand the master brake cylinder is leaking (sweating) which has to be addressed. The car has been sitting for more than 10 years...yet the owner has still to decide to wake it up.

From a sealing point of view it's probably not a good idea to leave one side of the system dry as failing seals could cause one to leak into the other.
The first step would certainly be to fix the master cylinder but as long as he can't decide about it ..

[goldnsx]

It's his car, so his decision to wake up the whole car...

[Kaz-kzukNA1]

If your NSX is 97 JDM AT, then the VIN is NA1-140*** and you have 2nd gen classic ABS.
The overflow happened while you were driving and triggered the ABS long enough last time. You just parked the car afterwards.
2nd gen ABS package is far better than the original 1st gen spec against the leaky solenoid issue but still, not free from it. It will happen if not exercised regularly.

You may have multiple issues with your ABS.
For sure, the air in the accumulator and possibly, the leaky solenoid.
Hope your accumulator bladder doesn't have pin hole….
At this stage, your ABS pump seemed to be at least operating fine.

Not sure how often you drive your NSX but after you parked the car for many weeks, you may hear the sound of ABS pump just after leaving your garage.
Starting the engine is not enough, one of the rear w/speed sensor (not VSS) must see the pulse over about 5mph before the ABS controller activates the ABS pump.

It depends on how long you parked the car and how bad the solenoid leakage is so there is no single diagnosis method for every scenarios but broadly speaking, if the ABS pump stops in less than 5sec, your leakage is not too bad. The longer the pump runs, the worse the condition is.
If the ABS pump kept running for 120sec, it would trigger the ABS warning light and ABS would be disabled.

Another thing you can do is to check the fluid level of ABS reservoir when you are likely to park the car for many weeks.
If healthy, the fluid level won't increase even by 1mm and stays the same over 3 - 4 weeks.
With very-very leaky solenoid, you will see the fluid level going up in just after 1 week.

If you lost the high pressure nitrogen gas behind the bladder of the accumulator because of pin hole, etc, eventually, the pump won't be able to reach the threshold pressure within 120sec and will trigger the ABS light. There is no cure apart from replacing or re-charging the accumulator.

The problem with the classic ABS is the combination of the way it is controlled (logic/software) and the actual hardware design.

The ABS pump won't kick in until it hits the specified threshold. If you have leaky solenoid but the accumulator pressure just sits above the threshold, you'll start the journey with the ABS reservoir above the max line.

Even a tiny single bubble inside the accumulator will turn into millions of bubbles when passing through the solenoid valve.
Before all of these bubbles disappear, the ABS pump kicks in and push back all these bubbles into the accumulator. Repeat this and you have lots of air inside the accumulator and thus, next time when you trigger the ABS long enough, you will have overflow resulting in fluid coming out of the reservoir cap.

The worst scenario is, if the classic ABS was triggered long enough, you could lose the ABS assist completely resulting in full lock condition until you release the brake pedal.
Asking this to ordinary driver under panic braking condition is almost impossible.

I tested this on the proving ground skid pad and snow covered long down slope.
The ABS kicks in while keeping the foot on the pedal.
You keep pressing on the pedal and there are kick-back so the aerated fluid is getting into the reservoir. Sooner or later, the ABS pump is activated and will force all these aerated fluid back to the accumulator but because you are still applying hard braking, the ABS is still triggered and thus, keep sending the aerated fluid to the reservoir.
You are still applying the brake pressure and the ABS pump keeps sending back the aerated fluid back to the accumulator but because of lots of air inside there, the kick back gets weaker and weaker.
It feels as if the brake pedal getting closer to the floor.
Eventually, your foot force will overcome the full of air accumulator fluid and thus, no more ABS.
This is one of the major reason why I upgraded my classic ABS to the modern one body Bosch style.

You can find the well-known flushing method through danoland website.

However, that method won't flush the piston side of the fluid.
You must activate both the inlet (NC type) and the outlet (NO type) valve simultaneously to get rid of the remaining air in the system.

There are very rare cases of ABS piston failure reported but it can happen.
At least one owner experienced the ABS fluid leaking from the slider piston chamber and leaked outside.

On NSX Prime, the owner reported that the ABS fluid did mixed up with the main brake side resulting in increased master cyl fluid level VS reduced ABS side and vice versa.

Both cases can happen with the failed seal at the slider piston.


Kaz