No left front brake

[nutonsx]

I have noted before that my car pulled to the right a bit under braking. Now it pulls hard and I have found there is no braking on the left side at all. After a hard braking test session, which did cause the antilock brake to activate, the rotor was stone cold. The right front was hot. Rears as well.

I have had the system flushed and bled in the past year. I have caused the system to activate routinely just to keep it free.

Does anyone have an idea as to what is wrong. It seems wrong that the antilock system should cause this as it is now very dangerous as the car at 60+ wants to leave the road when braking. All the press about these systems say the only failure mode is you just don't have antilock. But the symptoms point to the antilock as it is only one side with a problem and this is the only thing between the master cylinder and the caliper.

By the way, I did pull the caliper and was able to push the pistons back with the bled screw open so they are free. But with the caliper in my hand and the brakes engaged the the pistons did not advance.

Thanks.

Bill

 

[Larry Bastanza]

Bill,

The obvious answer is "frozen caliper", but your last statement seems to eliminate that possibility. Why did you open the bleeder valve to retract the piston though? Was it not moving by pressure unless you opened the bleeder? This sounds really strange, but if the piston would not go back with the bleeder closed, there may be some type of obstruction in the line from the master cylinder?????? I would disconnect the line from the caliper and see if you are actually getting pressurized fluid out of it.

I will check to service manual tonight and see if I can made any sense out of this. This will be one for the books. You may wish to contact Mark Basch at Basch Acura in AZ.

HTH,
LarryB

 

[nutonsx]

I am not sure if the piston would have retracted without loosening the bleeder screw as I did not have the right tools to retract them as I normally would on other cars. I could not get any thing to fit correctly, so I just loosened the screw. But it is very possible that they would not retract anyway as I would think the fluid is blocked in both directions.

The piston moved very easily with the bleeder open, it was not stuck whatsoever.

I am thinking it will be the anitlock, but I certainly am hoping it is something else.

Thanks for your interest and help.

Bill

 

[ScienceofSpeed]

Did you bleed that side well? If you had the bleeder screw open, you may have introduced a lot of air into the channels. Start at completely bleeding the system well.

You may wish to use a different colored brake fluid so that you can see when you have completely evacuated the current fluid.

ATE SuperBlue = Blue
Castrol Syntec Dot4 = Clearish yellow

-- Chris

------------------
Chris Willson
www.ScienceofSpeed.com
www.NSXClassifieds.com

 

[Larry Bastanza]

Bill,

Chris does bring up a good point, a full bleed is in order.

One thing you could also do after a full bleed, IF the problem is not cured, is to deactivate the ABS. I recall you can drive the car with the handbrake on for a few feet and the ABS light will come on indicating the system has detected a malfunction and is shut down.

Go to: http://www.nsxprime.com/FAQ/Technical/disabletcsalb.htm for details


If you leave the ignition on after that, you can repeat your brake testing. If you end up in the same situation, this will tell you it really does not have to do with the ABS.

Also, is your ABS pump chirping? Is the fluid level correct for the ABS as well as the main reservoir? Is your ABS reservoir wet on the outside? (this would indicate a sticking selonoid)

I agree with Chris, lets get back to basics first, before thinking it a complicated ABS problem.

HTH,
LarryB

 

[ScienceofSpeed]

While you're bleeding, you should buy Speedbleeders. They are a god-send. www.SpeedBleeder.com

These replace your bleed valves with a device that has a check valve, so air will never be 'sucked back' into the caliper. Also allows a one man bleed job.

Just around $6.50 each with the club discount.

-- Chris

------------------
Chris Willson
www.ScienceofSpeed.com
www.NSXClassifieds.com

 

[Lud]

The ABS is a pretty fail-safe design. I agree with Chris and Larry - look to the basics first. If you disconnect the line from the caliper, is there any fluid in it? If not, there is probably a hose failure. If there is, can you pump fluid through it (even a little) by pressing the brake pedal? If so, do then do a full bleed, and try it again, etc.

Let us know what you find!

 

[nutonsx]

Good thoughts from everyone. I am not ordering the ABS modulator yet! I did bleed the side a bit as with depression of the brake pedal I could get some fluid out. I have bled brakes often and am familiar with the procedure so I am fairly confident that I did not introduce air. Also, with the ignition off I had my helper (son) depress the brake with the caliper off and in my hand. No movement. And as I said earlier the other rotors were quite hot after testing while the left one was cold to the touch. I will check out a good bleed as I was not trying to do a good job, just testing. But I will try this and look at all other suggestions.

I talked with Tracy Townsend today who said he has heard of this symptom before on a TL but not an NSX. He did seem to think it could be ABS related.

So keep thinking. I will post results just for the information, and of course help to get the car back on the road.

Thanks,

Bill

 

[Lud]

Let me preface this by saying I have never worked on any ABS system. However, after thinking about this some more, I can see how a failure in the modular assembly could cause this problem. The fail-safe mode is mostly in case of a loss of pressure on the high-pressure side or an electronic problem with the control unit; in either case, it simply shuts down in inactive mode so you retain normal braking.

What we know: The pressure to the caliper in question seems to be way too low. The problem has gotten worse over time.

The pressure problem could be caused by a lot of things: a failing hose, debris clogging a line, a caliper problem, or the ABS system being stuck in the "interrupt" mode for that caliper. But the failing line or debris in the system seem more in line with a failure getting progressively worse.

You already tested the caliper movement and didn't see fluid leaking out, so we'll assume it is not the cause of the problem.

If it's an ABS failure there are several things that could do it... but they all seem somewhat unlikely.

Probably the least likely: If the control unit was constantly telling the solenoid valve to activate that would do it.
But I expect that would trip the ABS trouble light when you turned on the car since it does a system diag of the control unit when you turn it on.

Somewhat less unlikely (?): If the piston was stuck in the "up" position it would keep the cut-off valve closed. That would give you almost no pressure to that caliper. Same for the input/output valves. I just am not sure how it could get stuck like that or even more how it would get progressively worse.

You can run each solenoid individually as a diagnostic test. I suspect that if you ran the front left one while pressing down on the brake pedal you would know if it was a stuck solenoid or valve; if it was, you wouldn't feel any kickback on the pedal like you would during normal operation.

Unfortunately the service manual says the module is not servicable. That doesn't mean someone who knew what they were doing couldn't fix one, but parts are not available from Acura - it is sold as an entire (expensive) assembly and it looks like a fair amount of labor to replace one as well. If it can be disassembled maybe something just needs to be cleaned??

If it were stuck open you could try flushing the high pressure side of the system, but I don't think that will be very effective if it is somehow stuck closed since the fresh fluid would not flow through the affected part.

However, I have a problem understanding how the stuck valve theory could explain it getting progressively worse. I guess this message is not really very helpful afterall. Maybe it will spark an idea from someone else?

 

[nsxman]

I believe Lud is on the right track. The "cut-off" valve in the modulator may be stuck open, which would cause a loss in pressure in the caliper hydraulic line.

Alternatively, one or both of the valves controlled by the solenoid are stuck. However, the brake system functions independently of the ABS. The modulator is the only common component, so I suspect you have a bad modulator.

 

[Larry Bastanza]

Bill,

As I mentioned this will be one for the books. One additional idea I had based on Lud's e-mail is that you should be able to bybass that modulator valve completely with a fitting and hose setup to match the two lines (in and out) of the ABS modulator. If you bypass the ABS unit completely you will have a direct connect from the master cylinder to the caliper.

I am thinking this would not be too difficult to do. I will check tonight in the manual for how they are conected. Sorry, could not get to the book last night as I thought!

IF you get braking back after the bypass then it is a sure bet the ABS unit is at fault.

LarryB

 

[nutonsx]

Well, I tried everything suggested except using a hose to bypass the antilock module as I figured I would make a H of mess and probably screw up the threads.

I gave up and took it to Goodson Acura today. I am afraid of this as they seem to like to replace everything in sight and run the bill up.

I ended up changing the shocks on the car myself as they insisted on four wheel alignment after the repacement. I did't think this was necessary, and after doing the work, I still don't. Different topic, I know.

I will post the results from Goodson when done, if I don't have a heart attack!!

Bill

 

[nutonsx]

I got my car back in fine shape today. It seems that it was necessary to bleed the antilock system with a special tool. An air bubble had caused the spool valve for the left front to hang "open?" and let the fluid bybass to a large degree. So while technically the problem was caused by trapped air, due to it's location it caused an unusual situation which is in fact related to the antilock. A situation I feel is advertisd on all anitlock systems to not happen. That is, a fault here that makes the car dangerous. No warning lights either.

As to my comments about Goodson, I retract my fears as they did fine by me. And fairly, as no one commented, I could be wrong about the alignment issue. If so, someone please tell me before I wear the tires out.

I will not hesitate to take the car back again. Wayne Galligan was the service writer and he was great.

Bill

 

[Larry Bastanza]

Bill,

Glad to see things are OK. I do the ABS bleeding once a season, need it or not. It is very easy if you have the tool (about $100) and a little help from DanO at www.danoland.com. He has an excellent write up on how to do this.

It IS probably a good idea to get an alignment when the suspension comes apart for any reason. Installing new shocks means things had to come apart, so you should be on the safe side and have it aligned. The NSX is VERY easy to align and I pay $60 for a full four wheel alignment at a Porsche race shop near me. Basically they charge me 1 hour labor. After aligning the rear suspension on a 911, it is a pleasure to set up an NSX.

If you blow through a set of tires, even $100 is well worth it!!

HTH,
LarryB