Question on DanO's ABS solenoid flush.

[NSXF1]

First let me say one of the reasons I bought this car, besides the obvious, was this web site. Lud is incredible, and the NSX community is unlike any other car group I know of! I've lurked here quite a while learning many things about my "mistress", the wife's knick name for the car.

My 92 with 84K has been running the ABS pump progressively more and more on start up. I had MB flush the system, which seemed to help for a while. I travel a lot, so the car sits for a week or two in between drives. Lately, after start up, the pump has cycled on and off every 5 min or so unless you engage the ABS. Once engaged, it quits and is good for the rest of the weekend, maybe two. I figured this was a sticky solenoid, so I decided I would try DanO's excellent ABS solenoid work out. Before starting the procedure I noticed a few "shiny bits" in the reservoir. (Can't be a good sign?) Sucked all those out, put new fluid in and worked the solenoids, didn't have the T-handle to do the complete flush. After I finished, went out and "exercised" it. When topping off the fluid, I saw the same type of bits back in the reservoir, and it hasn't improved much.

Do I need to be looking for an ABS pump, or should I just do the complete procedure again? Anyone else who's done this seen the same thing? TIA

 

[DanO]

Hello and welcome! The NSX FAQ and the NSX community was one of the reasons I felt comfortable buying my “mistress” too!

Other than above average pump cycling, does your ABS work ok? No wheel lockup? No ABS fluid in the front compartment around the reservoir? If things seem to be working fine then it may not be a pump or solenoid (ABS module) problem, it may be that the accumulator is somehow losing pressure (the accumulator is the ball-shaped thing that hangs below the ABS module next to the pump). If the pressure in the accumulator falls below a certain point then the pressure switch will turn on the pump. Sounds to me like the pump is turning on quite a bit, which indicates that there may be a pressure problem and not a solenoid problem.

Woops, just reread your post. OK, once you exercise the ABS system, it seems to work fine for a few weeks. This would suggest to me that you may have a bad seal on the inlet valve (see SM page 19-35) which allows the ABS fluid to cycle through the system and loose pressure and once you exercise the system this valve reseats and forms a better seal and everything is ok for awhile.

If it were me, I’d try the solenoid workout some more with a few (or a case) of fresh brake fluid and flush the fresh fluid past each solenoid as many time as possible. If the little debris you are talking about persist then there may be some other problem with either the module, pump or accumulator.

Good luck and keep us informed!

DanO

 

[Lud]

As DanO said (and as it sounds like you already know) the pump only runs if the accumulator has lost pressure.

Debris in the system can cause valves to not seal up nice and tight which could certainly cause a pressure leak. You're going to need at least a very thorough flush of the system to get that all the stuff out of there or you're just going to keep having problems. That means using the T-bleeder and cycling the ABS system to flush fluid through it. This is a nice simple afternoon project if you can borrow a T-bleeder from someone (there are a couple loaners floating around out there).

Of course another concern is what is the debris and why is it in there to begin with? Whatever it is, you're right it probably can't be good. Is it metal shavings? If they reappear after you have flushed the system really well, it's probably a sign that part of your system is self-destructing. At that point my best recommendation is to take it back to MB and update him on what's going on.

P.S. Welcome aboard!

 

[DanO]

You may be able to get away without the t-bleeder wrench if you keeping on sucking out the fluid with a turkey baster after opening the solenoid with the switch. This is kind of like a poor-man’s bleeding procedure. If you think you’d rather have the t-wrench and don’t want to buy one or can’t find one nearby, let me know and I’ll ship you mine. [email protected]

DanO

 

[NSXF1]

Thanks for the reply guys. I thought maybe I made my judgement on the system a little too soon. Now when I take off after the car has been sitting a while, I push in the clutch as soon as I hear the pump come on to hear how long it runs. Since I started doing this, the pump now runs twice, the initial time and once more before I get out to the main road, then it stops. Is there a wheel speed at which the pump comes on, and if you slow down, I'm guessing it waits until you pass that speed again? Any way, took the car to go visit a friend in Prescott this weekend and the pump ran again until I looked the brakes and got the system to cycle.

The bits in the resevoir look like brass specs? Do either of you know if the inlet valve your talking about or the solenoid valves are brass? I'm probably going to try a full flush and more solenoid work before I give up, and take it back to MB. If there is a T-wrench floating around, I was on a list quite a while ago and never heard back. DanO, if you have one you can spare for a week or two, I'll send you an e-mail with my address. (Not sure how much Google picks up these days, and I'm down to one address that doesn't get spamed, so I don't list it.) Thanks for your help!


[This message has been edited by NSXF1 (edited 10 March 2003).]

 

[DanO]

I don’t have direct knowledge of the internal ABS module anatomy so I can’t answer your question regarding the makeup of the inlet valves. If anyone has a defunct ABS unit laying around, I’d love to dissect it!

regarding the t-wrench, no prob. send me an email w/ your address and i'll ship it out.

DanO

 

[Soichiro]

The pump does not depend on road or engine speed to turn on. It turns on when the engine is running and the pressure needs to be replenished. It will time out after 120 seconds operation even if the pressure has not built up properly. Perhaps that is what you are hearing?

 

[Larry Bastanza]

Soichiro,

Respectfully, I have to disagree in regard to road speed. The ABS system will not start the pump until it checks the pressure which will not happen until above 6 mph (10Km/h) according to the service manual, page 19-32.

Below 6 mph the system is not enabled at all to avoid low speed premature brake pressure loss. Once the system is engaged, it checks the pressure, if low, it will start the motor for 120 seconds, if the pressure is not up by then, ABS light will light.

I have found this also in practical experience, since my pump only starts once I am up my driveway, not while it is warming up stationary.

My $.02,
LarryB



[This message has been edited by Larry Bastanza (edited 10 March 2003).]