Early ABS modulator servicing

[OLDMNSX]

Just thought that I would update you early NSX owners who are looking for some relief for your malfunctioning ABS systems.

After getting to pay the mechanic at the local dealership to service my ABS unit twice, and the pump still cycles, I have taken on the crusade to fix my ABS unit. I have purchased a non-functional modulator (dissassembled and figured it out) purchased the Acura T-Handle ABS bleeder tool, made up the wiring harness (Dano DIY, Thanks Dano) and, I recently purchased a complete ABS system from another Prime Member, that I am going to use as a bench test unit to pressure test modulators, pressure switchs, pumps, solenoids and accumulators.

I am in the process of building a pair of blocks to flush/back flush the early solenoids.

I plan on dissassembling the module in my car, cleaning the inside of the housing, flushing the solenoids, reassembling the whole unit and pressure testing. I will then monitor it, under pressure, for a couple days to verify the service. If I am successful with all of this, I have two other modulators to do the same with.

My ultimate goal is to fix my ABS system and to help other NSX owners that are having problems keeping their early ABS systems operational at a reasonable cost. I am getting very excited about this whole thing.

I will see how much time it takes to do this and come up with a fair cost to offer to other members. Let me know what you think.

Brad

 

[nh_nsx]

Thanks very muich for doing this Brad!

Please keep me posted on your success as I am currrently having issues with my ABS system...

-Randy

 

[Danny_Ocean]

I did read a few other posts, but still not sure. How would I know for sure if my ABS ('93) is acting up?

 

[jagtiger]

Brad,

My ABS warning light has been "ON" for the longest time. I'm really glad someone finally took the time to look into this. Good luck on the project:smile:

 

[ChopsJazz]

Coll project. Mine doesn't "act up", but it does cycle upon start-up the day following any ABS usage.

 

[SENNAF1]

Well Brad just hooked me up ,we got my ABS working flawlessly after a year of ownership with out it.If any one is going to figure this system out its Brad.Thanks again Brad.Myron

 

[warrenw]

Hey Brad,
My '91 cycles and clicks just about every time I drive the car for about 20 - 30 seconds, then it is quiet. No ABS light on dash.

What exactly is the cause of this?

The previous owner had the ABS flushed every 5 years or so to correct the issue, but I am not sure if I sould ask the dealership this spring to do the purge and flush of the ABS.

I may have to do a drive to Boise!

 

[OLDMNSX]

Hey Brad,
My '91 cycles and clicks just about every time I drive the car for about 20 - 30 seconds, then it is quiet. No ABS light on dash.

What exactly is the cause of this?

The previous owner had the ABS flushed every 5 years or so to correct the issue, but I am not sure if I sould ask the dealership this spring to do the purge and flush of the ABS.

I may have to do a drive to Boise!

Warren,
It sounds like maybe just a flush and cycle of the solenoids may fix your problem, the system is working properly. Open the reservoir for the ABS and look at the fluid. If it is real dark you need to do a flush. There may be a small amount of air in the system also. When we did SennaF1's system it had a LOT of air in it.

Have you put the car into storage for the winter? If not, you could get it out on a snow covered surface and cycle the ABS a few times this may take care of your problem. Get the car going 10-20 MPH and apply full brake pressure. You should feel the brake pedal pluse numerous times. Do this 4 or 5 times. Check the ABS reservoir for foamy fluid or low fluid level when you get done. This may allow the seal in the "leaky" solenoid to reseat.

If it has been 5 years since a complete flush and cycle, it is time to do it.

When it warms up again and the roads clear, it would would be great to see you in Boise. If you think that you want to wait to do the flush till then save the money that you would spend and the dealership (mechanic) and drive to Boise. We can do it then.

Brad

 

[warrenw]

Brad,
the last purge/flush was done in May, 2004 5000 miles ago. It was also done at 8000 miles when the car was 3 years old.
The car is stored for the winter.
I will take a look at the fluid, but I doubt if it has discolored in 4 years.
I checked the manual, it does appear to be too difficult, except for the bleading tool and switch jig to run the pump. I would assume that you need to purge a lot of fluid to get the job done right.
Any comments on the brand of fluid to use?

 

[OLDMNSX]

Brad,
Any comments on the brand of fluid to use?

I don't think that brand is as important as "CLEAN". Consider that the fluid in the ABS system never goes anywhere other than from the ABS reservoir to the pump, gets pressurized, into the modulator (accumulator included here), thru the solenoids, around in the modulator and back into the ABS reservoir. It never gets hotter or colder than the temperature in the front compartment of the car. Without the extensive temperature fluctuations the fluid is less likely to absorb moisture, so I think that clean fluid that is free of any air bubbles is all that is required.

I usually plan on using 2 Qts of fluid to flush the system. I am working on making a couple attachments to use in place of the OEM reservoir to use just for the flush that may save some fluid. More to come on this. I just need more free time and less work...................NOT!

Brad

 

[OLDMNSX]

UPDATE: Over the last couple weeks I have made a couple parts to improve the quality of the ABS flush process. After doing SennaF1's ABS system I came up with an idea that would improve the process. Keeping the aerated dirty return fluid from mixing with the clean fluid would save fluid and do a better job. Here is what I came up with in the pictures. You just remove the OEM reservoir and replace it with the Honda Master Cylinder reservoir with adapter and the fitting and hose in the return port. These two attachments split the in coming and out going fluid. You do the flush, and then replace the OEM reservoir and fill it with fluid.

Brad

 

[nigel]

Hey Brad. Thanks for the mention in "jreheners" thread.
I already have spare reservoirs and access to a lathe and mill. Where did you get the plate the reservoir and return line plug fit into? Is it an altered manifold from another reservoir assy.? I'd like to give making one of these kits a go. Seems this is the easiest way to solve the ABS problem. Good job!!

I am working with a retired W-4, Apache driver, IP, platoon leader, Marcus,(Mark) Gann. Great guy!! I know it's a big service but the Apache drivers are a smaller community. Just thought i'd ask. I don't know your last name so I couldn't ask him the same. He did time in the desert, Germany, Rucker, etc, etc...
Also, I'm thinking of going to Air-Evac Lifeteam in Missouri until they get a hospital contract in Florida. This cold is kicking my butt after all those years where cold is 50f for two days.
I realize this should be in a p/m but what the heck.

Cheers
nigel

 

[OLDMNSX]

Where did you get the plate the reservoir and return line plug fit into? Is it an altered manifold from another reservoir assy.?

It is just the top off of the OEM modulator that sits on top of the solenoids and the OEM reservoir sits on top of it.

Brad

 

[KoolinNSX]

How's the project coming along?

 

[MvM]

Hello Brad,

Since you seem to know and understand the ABS-system very well, I have a question for you.

Ever since I upgraded my brakes, it sometimes seems that the ABS-system has trouble performing as it should. I often brake hard and sometimes I can get the front wheels to lock up, as if the ABS-system isn't there.

Lately, I have also noticed that I can get my rear wheels lock-up, which is very annoying because when that happens, the tail tend to come around very quick. And that is while I have the standard 303x23mm rotors in the rear versus bigger 324x28mm rotors in the front.

Is this caused by a bad sensor or is it just the fluid and/or solenoids. Like said, my ABS-systems sees a lot of work, I guess it has to kick in at least once every week (if only to test my grip on the road). Usually, the next day I will get about 10 seconds of the pressure pump when starting the car, but not for any longer. Also, when I do NOT use the ABS-system, it also will not activate the pressure pump.

Any ideas or advice would be much appreciated.

 

[OLDMNSX]

How's the project coming along?

The GOOD NEWS is I have a guy with a computer controlled milling machine making me a pair of blocks that will allow me to back flush the early (91-92)modulator solenoids. Yesterday I had the hoses made up to be able to pressure test the accumulator and pressure switch, and also a hose to use for the solenoid back flushing. I have all of the electrical parts to build the power switching box to power the pump and acutuate both valves in the solenoids.
If you look at the maintenance manual (Pg 19-35 and 19-36) you will see that the solenoid has a "normally OPEN" valve at the top to allow fluid to flow from the acutators back into the reservoir after actuation. It also has the "normally CLOSED" valve that controls the high pressure fluid that works the actuators which gives us the anti-lock function.
I now have two, three counting the one in my car, complete ABS units. That is the modulator, accumulator, pump and pressure switch. One of the units is off of a 92-99 model car. This will allow me to do a complete familiarization with this later type of solenoid.
My timeline to have this project up and running has had a setback. I have been having to spend a lot of time taking care of my fathers personal stuff since his heart attack the first of December (still alive, just in a nursing home). Like two days last week, two days this week, I think you get the idea.
Once I get the solenoid flush blocks done I can have the hoses made up and hopefully by then I will have the electrical box done.
I loaned KELLY in Florida my flushing tools and he was able to return his ABS system back to being fully operational. He was my first tester for the separate reservoir and solenoid return fluid adapter (pictures in previous reply). The reservoir needs a minor modification to keep from having to remove the cruise control box (5 bolts)that mounts near the ABS. I didn't take this into account when I made the adapter. My car was in it's winter "cocoon" and I didn't do a final fit.
Anyway, long story to a short question, but it is still hot on the burner.
Brad

 

[Kelly's NSX]

Thanks again Brad for the use of your tools. Your tools and advice got my nsx abs system back on track. Thanks again. For all other NSXers out there wondering....if any one here can do it, Brad can. Sorry to here about your father.

 

[OLDMNSX]

Hello Brad,

Since you seem to know and understand the ABS-system very well, I have a question for you.

Ever since I upgraded my brakes, it sometimes seems that the ABS-system has trouble performing as it should. I often brake hard and sometimes I can get the front wheels to lock up, as if the ABS-system isn't there..

MvM, First off, what year car are we talking about here? Now, when you say "upgraded" brakes what did you do? Also, what size tires do you have? Something to remember is that the engineers designed this ABS system around the stock brakes and tire size, also tire compound is a factor. That is, caliper clamping force and tire diameter. When you change these two variables you start to change the whole equation built into the system computer. When the equation changes the performance of the system is going to change. So if the front and/or rear calipers operate more effeciently, possibly at a different bias, than the stock calipers it may be easier to get the wheels to lock up before the ABS computer can compute a loss of rotation and then provide the required amount of pressure relief (kick back) to allow the wheel to begin turning again. Wheel diameter does not matter, just outside tire diameter.

Lately, I have also noticed that I can get my rear wheels lock-up, which is very annoying because when that happens, the tail tend to come around very quick. And that is while I have the standard 303x23mm rotors in the rear versus bigger 324x28mm rotors in the front..

Now here, what are the road surface conditions when this occurs? Is there any sand or loose material on the road surface that would allow for a loss of traction. What is the compound that your tires are made out of? I know that a hard tire will break loose much easier than a sticky tire.

Is this caused by a bad sensor or is it just the fluid and/or solenoids. ..

If you do not have an ABS light illuminated I would say that your sensors are just fine. When was the last time that the fluid was changed in the ABS and the solenoids flushed? It may be time.

Like said, my ABS-systems sees a lot of work, I guess it has to kick in at least once every week (if only to test my grip on the road)....

How many sets of tires do you go through in a year? Are you a professional race car driver full time? Do I watch you driving F1? :biggrin: If you have an aggressive driving style you are going to be operating at the upper limits of the early ABS system capabilities.

Usually, the next day I will get about 10 seconds of the pressure pump when starting the car, but not for any longer..

I would say that if the pump is running the next day after an ABS event that you may have one of your solenoids leaking a small amount. If it is leaking even a small amount the functionality of the system may be degraded.

Also, when I do NOT use the ABS-system, it also will not activate the pressure pump..

If I understand you right here, you are saying that the pump DOES NOT run regularly when you haven't had to use the ABS. If this understanding is correct, the system is functioning correctly. This is the way it should be. The only time the pump should operate is to re-pressurize the system, up to the amount required by the pressure switch. (I am in the process of figuring out what this pressure is. The manual does not give a specific pressure. If someone knows what the pressure is, please let me know. That will save me some time.)

Any ideas or advice would be much appreciated.

The ABS system in the 2000+ year cars is an improvement in ABS performance. This may be an option. I know that at Science of Speed you are looking at around $1700 for the kit. I don't have a specific number for who has done it the cheapest.

I hope that some of this helps.:wink:
Brad

 

[MvM]

MvM, First off, what year car are we talking about here? Now, when you say "upgraded" brakes what did you do? Also, what size tires do you have? Something to remember is that the engineers designed this ABS system around the stock brakes and tire size, also tire compound is a factor. That is, caliper clamping force and tire diameter. When you change these two variables you start to change the whole equation built into the system computer. When the equation changes the performance of the system is going to change. So if the front and/or rear calipers operate more effeciently, possibly at a different bias, than the stock calipers it may be easier to get the wheels to lock up before the ABS computer can compute a loss of rotation and then provide the required amount of pressure relief (kick back) to allow the wheel to begin turning again. Wheel diameter does not matter, just outside tire diameter.

Hi Brad,

For starters, thanks for the lengthy reply
My car is a 1994 NSX Coupe.
The brakes I am currently using is the Racing Brake upgrade kit.
In front I have the 324x28mm rotors, in the rear the 1997+ size at 303x23mm rotors.
The tires I am using are the Falken FK452 tires. Most people seem to think it's a 2nd grade tire, but I find it comparable with the Bridgestone PP S03 I used before.
Tiresizes I am using are 225/35ZR17 in the front and 265/35ZR18 in the rear.
I have been using the Hawk HP+ braking pads both front and rear.

Now here, what are the road surface conditions when this occurs? Is there any sand or loose material on the road surface that would allow for a loss of traction. What is the compound that your tires are made out of? I know that a hard tire will break loose much easier than a sticky tire.

Road type is just the usual, good quality tarmac (asphalt) roads. However, I have recently replaced by front brake pads from the Hawk HP+ to the Axxis Ultimate pads. These pads defintately have less bite than the HP+ pads.
Also, I did notice that, with the HP+ pads, usually, my right front tires would lock up (or ABS kick in) just before the left front tire. I was told this is not unusual, because in a LHD car, there is more weight on the left front wheel.

If you do not have an ABS light illuminated I would say that your sensors are just fine. When was the last time that the fluid was changed in the ABS and the solenoids flushed? It may be time.

So far, I have only flushed the normal brake fluid, but never the ABS fluid. Maybe it's time to do that. How can I check my solenoids?

How many sets of tires do you go through in a year? Are you a professional race car driver full time? Do I watch you driving F1? :biggrin: If you have an aggressive driving style you are going to be operating at the upper limits of the early ABS system capabilities.

I use about one set of front tires and two sets of rear tires every year. This is in about 12000 miles. I am NOT a race car driver, but I do drive my car fast, love to take those corner at speed. My alignment is OEM in front and with -2 degrees camber in the rear and 5mm of toe-in.
I DO used my brakes a lot and use them hard. I have not done any track events in the last year but I did managed to go through a full set of the Hawk HP+ pads in the front. And, to be honest, it seems that I have also worn out my front rotors (those new Racing Brake ones I just mentioned) in just 13082 km or 8176 miles. Very annoying to say the least

I would say that if the pump is running the next day after an ABS event that you may have one of your solenoids leaking a small amount. If it is leaking even a small amount the functionality of the system may be degraded.

If I understand you right here, you are saying that the pump DOES NOT run regularly when you haven't had to use the ABS. If this understanding is correct, the system is functioning correctly. This is the way it should be. The only time the pump should operate is to re-pressurize the system, up to the amount required by the pressure switch. (I am in the process of figuring out what this pressure is. The manual does not give a specific pressure. If someone knows what the pressure is, please let me know. That will save me some time.)

I was always under the impression that the ABS system functions normally. Pumps switches on every day after heavy use and otherwise occassionaly.
For the record, my car is garaged and I have yet to notice any kind of fluid leaking on the floor.

The ABS system in the 2000+ year cars is an improvement in ABS performance. This may be an option. I know that at Science of Speed you are looking at around $1700 for the kit. I don't have a specific number for who has done it the cheapest.

I hope that some of this helps.:wink:
Brad

Do you have experience with the effectivenss of the 2000+ ABS system. Do you think the upgrade is a worthwhile one? If possible, I would like to get the shortest possible braking distances at a reasonable price. With the RB upgrade, my confidence in the brakes has improved dramatically over OEM and I have had full confidence to hit my brakes really hard at 150 mph. However, if the strain is causing my ABS to act up or behave unreliable, the story changes that of course.
After all, It's much better and saver to have a car remaining stable under heavy braking with a little less braking than a car that will spin out because one tires is locking up.

 

[OLDMNSX]

MvM,
From what you have told us it sounds like you drive your car at the far extreme of the capabilities of the 94's ABS.

One thing that I would suggest is do a comparison of the diameter of the OEM size tires to the ones that you have now. See if the ratio between front and back tire diameter are significantly different from OEM sizes to current. If there is a large difference in ratio this could be some of the poor performance of the ABS. The computer is taking longer to recognize a need to make inputs.

I do not have any experience with the 2000+ ABS upgrade. I have read on another thread that the guys that have done the upgrade rave about the performance improvement. This may be the way to go.

In order to flush your current ABS system you will need a Honda T-Handle bleeder tool and will have to look up the ABS DIY that was done by DanO and make up the wiring harness to cycle the solenoids. Do a search for ABS and it should show up. The solenoids on the 93-99 ABS are a little different from the 91-92 ABS, but they do the same thing. I recently received a 93 ABS modulator unit and haven't had time to disassemble it to see the differences.

Brad

 

[MvM]

Hi Brad,

Thank you very much for your input so far. When I first had put on the Racing Brake brake upgrade, the brakes performed beatifully.
As a matter of fact, though I have worn out a full set of Hawk HP+ front pads and a set of fronts rotors as well, the tires are still ok and have enough thread left on them to drive around with.

I will first see that I do a correct ABS flush and see what the results will be of that.
Is there anything at all to check on the wheel-hub side. Perhaps connectors or dirty sensors that need cleaning after heavy use??

 

[goldNSX]

Ever since I upgraded my brakes, it sometimes seems that the ABS-system has trouble performing as it should. I often brake hard and sometimes I can get the front wheels to lock up, as if the ABS-system isn't there.

Lately, I have also noticed that I can get my rear wheels lock-up, which is very annoying because when that happens, the tail tend to come around very quick. And that is while I have the standard 303x23mm rotors in the rear versus bigger 324x28mm rotors in the front.

Hi Marteen,

The ABS has to see a wheel about to lock up before it can react. So a wheel lock-up of the cause of the source which is traction related -> see your rear wheels.
From what I see is that on a 94 the wheel size ratio is not perfect. With 225/35/17 in the front I'd go with 255/35/18 in the rear. I once had a similar ratio and nearly lost the hole car while braking hard during a turn with the front wheel about to lock but the ABS was sleeping.
I also believe that you can improve the brake distribution on the car. You've changed quite a lot on your brakes, it's try and error.
Hard braking is ok but not optimal, esp. with the wheels locking up. Race drivers try to avoid this. With ABS the car gets unstable and that's the worst thing you want under hard braking.

 

[MvM]

Hi Marteen,

The ABS has to see a wheel about to lock up before it can react. So a wheel lock-up of the cause of the source which is traction related -> see your rear wheels.
From what I see is that on a 94 the wheel size ratio is not perfect. With 225/35/17 in the front I'd go with 255/35/18 in the rear. I once had a similar ratio and nearly lost the hole car while braking hard during a turn with the front wheel about to lock but the ABS was sleeping.
I also believe that you can improve the brake distribution on the car. You've changed quite a lot on your brakes, it's try and error.
Hard braking is ok but not optimal, esp. with the wheels locking up. Race drivers try to avoid this. With ABS the car gets unstable and that's the worst thing you want under hard braking.

Hi Thomas,

I understand what you mean. My point is, before the upgrade, I never had any real problems with the ABS-systems. Now I have done the upgrade, it sometimes feels like the ABS-system is not fully up to its task.

At least with the old system, AFAIK, the system works by putting a contra-pressure on the brakelines, thereby reducing the pressure the calipers are exorting on on the pads. This causes the wheels to momentarily unlock. The drivers literally can feel this 'back'pressure because the brake pedal is being pushed back by the ABS-system.
The thing I am wondering about is this.
If you have increased the capacity of your brakes (larger rotors/increased torque and/or increased brake pad friction), could it be that the ABS-system is not (always) capable of giving enough back-pressure to release the brakes if they lock up. Which would mean that your wheel could lock up, intermittently, depending on the pressure available in the ABS-system?

I agree that it is never good to actually activate the ABS-system, but in wet weather conditions and/or uneven road conditions it is easy to get the wheels lock up, especially if you have upgraded the brakes.

 

[OLDMNSX]

Hi Brad,

Thank you very much for your input so far.

Marteen, You are welcome. Remember, I am learing as we go here too, especially when it comes to aftermarket brake upgrades.

Is there anything at all to check on the wheel-hub side. Perhaps connectors or dirty sensors that need cleaning after heavy use??

I would say no here. The wheel sensors are magneticly interupted by the wheel hub pulser with a .4 to 1.0 mm air gap. Unless it has a lot of crap in there it should work just fine. The pulser and the sensor are a long way from the caliper and brake rotor so should not accumulate any large amount of brake pad dust.
Brad

 

[goldNSX]

If you have increased the capacity of your brakes (larger rotors/increased torque and/or increased brake pad friction), could it be that the ABS-system is not (always) capable of giving enough back-pressure to release the brakes if they lock up. Which would mean that your wheel could lock up, intermittently, depending on the pressure available in the ABS-system?

Could be. As Brad explained abve: if you change the equation where the ABS was built around...What I guess is that the back pressure of the ABS could be too high in your secenario IF you need less pedal effort with your BBK. Actually, what would you do without the ABS system?

BTW: My HP+ pads arrived today. :wink: