ABS fault fix

[Midnight Blue]

As I reported earlier, I was having trouble with my ABS system on my 1995 model after the car had sat for a month. The pump ran for a full 2 mins, cut off and the fault light was activated. I checked the solenoids following the instructions from danoland.com/nsxgarage but after the first solenoid checked out could no longer build pressure by running the pump.

The good news for those who may encounter the same problem is that it is not necessarily either expensive or difficult to fix. I took off the pump and by connecting it to a bottle of brake fluid and some jump leads, found that although it ran well enough, it had almost no output.

The pump unit is easy to open up and is a very simple piston pump. There is a basic pressure relief valve built into the pump and this was jammed open by brake fluid residue, a sticky brown film.

A quick clean, reassemble, pressurise, flush of the solenoids and refill and everything is fine again.

I will flush the fluid out again in a few weeks to make sure that I have got as much of the residue out from the entire system as possible and in future, make sure the fluid is changed at regular intervals.

Regards,

Andy

[mart155]

Andy,
Glad you were able to fix your problem.
When you do the re-flush in a few weeks, how about taking some photos of the process and maybe do a quick 'how to' write up.
Regards
Martin.

[Midnight Blue]

Hi Martin,

I posted the info so anyone else might recognise the symptoms and avoid a nasty bill for pump, accumulator or modulator unit when it may well be only a dirty valve.

If you check out Dan's Garage, (the Danoland.com) link above, he has shown a comprehensive 11 page guide to exercising and flushing the ABS system.
This also includes photographs of the wire connectors you need to make to activate the solenoids and of the flushing and bubbling up of the brake fluid. It is for a LHD car but nothing is all that different, just on the other side of the car.

The wire connectors are only are only a couple of small crocodile clips and a switch so nothing too time consuming. I would guess I took about an hour to flush out the system and refill twice after I had made the wires.

There is no way to drain the fluid without removing pipes and it has to be sucked out of the reservoir. He suggests using a turkey baster to remove the old brake fluid but I used the hand pump from the inside of a hand soap dispenser to pump the old fluid out from the reservoir into an old bottle for disposal. It rather conveniently had a 6 inch length of hose under the hand pump to get right to the bottom of the reservoir. (You need to take the filter unit in the reservoir neck out first.)

Cheers,

Andy

[mart155]

Thanks Andy, No point in re-inventing the wheel is there :D

[Martyn27_uk]

Hi Andy,

Did you have one of the T-brace thingys to open the maintainance bleed valve? Any chance of some hints or pictures about the pump removal and replacement? In particular, how did you re-pressurise the pump after you'd cleaned it out?

I've done the solenoid trick from Danoland and the pump is still cycling. No ABS warning light but every time I slow down for a traffic stop the ABS system kicks in, the brake pedal shudders and then the pump runs for a few seconds to re-pressurise the system.

[Midnight Blue]

Did you have one of the T-brace thingys to open the maintainance bleed valve?

No, by exercising the solenoids until there was no more foaming in the reservoir, I knew that there was no pressure left in the system and it was safe to disconnect the pipes.

Any chance of some hints or pictures about the pump removal and replacement?

Sorry, didn't take any pictures when I did the job but the removal is fairly straightforward. There is a low pressure hydraulic pipe that leads down to the back of the pump. It has a screw type clip. I took that off and the fluid from the reservoir drained out.
There is a high pressure hydraulic pipe, (looks like a rubber brake hose) that leads from the pump to the modulator. I took that off at the banjo joint at the modulator leaving about 15 inches of hose on the pump.
There is the electrical connector from the pressure switch to disconnect and the one for the pump motor, which is a bit fiddly to get at and then the three bolts that you get to from underneath and whoops, there you are with the pump, all fastened into a three legged frame sitting in your hand. Pay attention to how the three bolts go together with their rubber washers and metal plates so you know which order to put them back in. You can now get at the bolts that hold the accumulator and pressure switch on. It's fairly heavy, the accumulator is like a little cannon ball.

The accumulator is held on to the plate with the pressure switch by 3 bolts if you need to remove it. It seals with a O ring seal on the neck protruding from the accumulator into the housing.

It was at this point I hooked up the pump to a bottle of hydraulic fluid and a battery and realised that the pump, despite running, was not actually pumping any fluid. The fluid level in the clear neoprene hose I used was just fluctuating up and down slightly with each pump stroke

In particular, how did you re-pressurise the pump after you'd cleaned it out?

Didn't really do anything special. I made some effort to leave fluid in the pump after cleaning and testing, but I just filled up the reservoir after refitting, allowed it to bleed out any air through the banjo to the modulator (which is above pump level) before I completely tightened it and it ran fine.


I've done the solenoid trick from Danoland and the pump is still cycling. No ABS warning light but every time I slow down for a traffic stop the ABS system kicks in, the brake pedal shudders and then the pump runs for a few seconds to re-pressurise the system.

You suggest that your ABS is activating every stop and then re-pressurising normally. Not sure what to suggest but it sounds to be more of a sensor problem rather than a hardware one.

Good luck, Regards,

Andy

[Andy]

Hi Guys

I have similar problems with the ALB on my 1991.

The pump has always been noisy. Running for about 30 seconds each time I set off then stopping with everything working normally. I assume this is normal (they are all noisy?)

Recently when I set off either :
a) The pump runs for 120 seconds then stops and the ALB light comes on. The car then runs without ALB for the rest of the journey, or
b) The pump runs for 10-15 seconds then stops, then runs again, stops, runs again and again. Today it ran maybe 20 times until I finally arrived home. On opening the bonnet I can hear a hissing noise from the left hand side while the engine is running.

I assume problem b) could be the pressure relief valve in the ALB pump is jammed open?
Would problem a) be a separate sensor problem?

Any help appreciated

Andy

[Midnight Blue]

Hi,

My first guess would be that one of the solenoid valves is not sealing correctly and the pressure is leaking away. (hence the ABS pump cycling).

Check out the Danoland link above for his brake guide and give it a good flushing.

Regards,

Andy

[Andy]

OK - many thanks

Andy

[Martyn27_uk]

OK, this is what happened next... I took K20 out on a wet and slippery road and ( in line with previous advice ) hammered the ABS over and over again. During emergency stop number fourteen ( or so ) I felt a very meaningful "CLUNK" come back through the brake pedal ( there was probably a clunky noise too )... for the next few weeks everything ran fine.

Last week the "foot massage at every traffic stop" problem recurred. I tried a few more heavy duty stops last night ( in the rainsoaked surgery car park after hours! ) - but no mighty "CLUNK" and no solution.

Is it worth trying again or should I try to have the unit dissembled and rebuilt in the way Midnight Blue describes ( I'm way too chicken to try it myself, humans I can cut up and put back together with consumate skill, but brake systems? Naaah! )

Alternatively, I have a chance to buy a second hand - but working - unit for just over £200 ( plus whatever I'd have to pay to get someone to install it )

Which option should I go for?

Rebuild - if i can find someone to do it or Replace - if I can find someone to install it!

[Midnight Blue]

Hi Martyn

It is not mechanically difficult to disassemble the ABS pump and accumulator....if it was, I wouldn't have been able to do it!

Whilst I am not a mechanic, I do understand how the seperate system ABS in an early NSX works.

Which part of the ABS system are you thinking of replacing?

It sounds that, as if the mechanical portion of the ABS is working correctly, (perhaps at inappropriate times), but nevertheless working. The pump is producing pressure, the accumulator is storing the pressure and the modulator solenoids are working. If, the pump only runs after the brakes are used, then this would imply that the solenoids are sealing correctly and not gradually leaking the stored pressure away. All of which implies that they are working correctly just being signalled to work too often.

If the bits you are buying include the modulator unit, then maybe, as it still could be a solenoid valve not operating correctly but otherwise it seems wheel sensor or wiring related.


Regards,

Andy

[Martyn27_uk]

The kit I hope to get my hands on is from a bloke who has upgraded his early model ABS system to the newer ( much simpler! ) system used after the upgrade. So the bits I'll get are the bits he's taken off! I've not really found out whether they'll include electrics or not.

The only things that make me think it's not an electrics / sensor problem are (1) the ECU isn't throwing any diagnostic codes (2) the ABS warning light is not glowing - except for the initial start-up check and (3) the problem really did settle down for a while after my first round of heavy duty braking - "working the system" as they call it ;-)

It really felt as if something that had stuck had freed itself for a while... which makes me think of valves in the internal workings rather than solenoids.

[goldnsx]

If you do the break-free method of slamming the brakes several times it's highly recommended to flush the ABS system right afterwards orelse the broken-free chunk will get it stick again sooner or later.

Even my trouble-free system used to like some panic braking twice a year to keep it's shape.

[Midnight Blue]

Hi,

Sorry for not being clearer in my explanation but we are talking of the same thing, electrically operated valves. Get a bit of dirt stuck in there, the valve is not fully closed and your pressure will leak away all the time causing the pump to cycle.

The exercising the solenoids procedure is connecting the battery direct to these electrically operated valves and back flushing any dirt up into the reservoir so it can be pumped out. It has a similar effect to what happens when you check the ABS in a wet car park but appears to be more thorough in cleaning out the system.

Cheers,

Andy