Hard brake pedal & seemingly no ABS/pump

[m666 edd]

I've been doing various simple servicing on the NSX (oil, cleaning air filter & throttle body) in readiness for Japfest and just drove the car fairly fast to test the new Yokohama AD08 tyres & was doing some hard braking (usually I'm very light on brakes on normal in traffic driving). I noticed the brake pedal felt a lot harder than I remembered. In the past I had a soft but good braking performance and then a progressive feel & further braking performance.

Further into my drive I pressed the brake really hard to test the performance and managed to get the tyres to lock up and make a pretty loud tyre screech! This was at about 40mph, I let off the pedal as soon as it locked. So the braking performance was there but the pedal needed a fair amount of effort.

When I got home I tested to see whether the brake servo was working so I pressed the brake pedal lightly without the engine running and then started the engine and the pedal went down further with the same applied pressure. Checked the vacuum hose under the bonnet and that was fine - Haven't checked the rest of the vacuum line. Brake pads seem to have about 4mm front and back.

I realised the ABS didn't seem to activate when the tyres locked up but I did release pretty quick. However when thinking about it I haven't heard the ABS pump the system in a long long time (could be months). I used to hear it at least once if I hadn't driven the car in a while.

The ABS light illuminates and then disapears shortly after the engine starts as it should.

So it seems I have a hard brake pedal and my ABS pump isn't pumping / working? I don't know whether these problems are linked. Can anyone shed any light on this?

Cheers

Ed

[PeteM]

Hi Ed,

Interesting one, sounds like you could have lost brake servo Vacum assistance. Any chance you have disturbed a Vacum pipe of the manifold by the throttle body ?

Would also say with 4mm left on the pads they could do with changing for the next track day. Abs fuses all ok in relation to the pump?

Regards Pete.

[NSXGB]

Check the solenoids with this procedure http://www.danoland.com/nsxgarage/brakes/abs/abs.htm . Would be rare for all 4 to stick at the same time though.
Sticky caliper pistons can cause a hard brake pedal too.

[Kaz-kzukNA1]

Hi, Ed.

I can’t remember what kind of brake calliper you are using but if you are on the OEM one, I hope you checked the pad thickness for both the outer and the inner one.

Not just for NSX but also for other cars with the same calliper movement design, the inner pad will wear much faster than the outer one.

With OEM calliper, if you have only 4mm at the outer pad, your inner one would be almost at the limit unless you have a problem with your calliper resulting in outer pad wearing faster than the inner one.

I have seen several NSX with this issue.

Inner pad seized to the calliper bracket and only the outer one was working hard to stop the car.


Brake system is converting the momentum energy into heat and brake pads are part of the heat exchange capacity so the wear rate at the pads accelerates dramatically especially after loosing more than 50% of the initial thickness.


Did you notice this change in pedal touch suddenly or eventually over many days/months?


Ideally, you should measure the vacuum pressure at the brake booster to check the functionality and the leak but your method is also a good way for a quick check.


While the engine is off, press the brake pedal several times to release the vacuum pressure and then press and hold the pedal down like you normally do at the traffic light.

Start the engine and if the pedal goes down a little, the booster is operating fine.


You have confirmed this and therefore, one side of the booster is fine on your NSX.


Now the leak check.


While the engine is running, once again press and hold the brake pedal as above and while holding the brake pedal, stop the engine.

If you don’t feel any force trying to push the pedal up, then the booster is not leaking.


Release the pedal and then press it again in a normal way a few times while checking the following point.


Every time when you press the pedal, you should feel that the pedal stops at higher point than the previous attempt.

After about 3 pedal strokes, you will no longer have the vacuum assist and thus, the pedal sits at high point and also you should feel very hard pedal touch.


This will confirm the operation of the check valve inside the engine bay near the fuse box.



If one of your pads (inner) is completely worn out, seized inside the calliper bracket, the piston is not moving smoothly or other issues with your brake system, you could get hard pedal touch but if you noticed the change in the pedal touch all of a sudden, may be something else....


I have test driven about 50 UK based NSX by now and I’m afraid none of them passed my brake test….


If your calliper was not over hauled within the last 3 years, I would consider doing it immediately if you have any question marks on your brake system.



Flushing the ABS system can be done using the link in NSXGB’s post and it is a good starting point.


However, there are lots of things not included in that procedure so you may struggle to check and flush the system thoroughly especially if you have some issues with ABS.

So many scenarios can be generated so almost impossible to cover everything in writing them here.


The ABS on earlier models is separated from the master brake system.


However, if you look at the structure diagram, failure at the ABS piston (not the calliper piston) will affect the performance of master system.


I read one case on NSX Prime and also another owner contacted me with similar case recently.

In either case, they were different from your case so I would first look at the master system and then the ABS.


Kaz

[Justin]

Kaz - I'd be interested to hear whether much braking is available on an NSX when the servo vacuum goes? I'm paranoid about this since the issue occurred on my student-days volvo 340 (!) and I had no capability to get the pedal down at all. Is the NSX stoppable without the servo do you know?

[NSXGB]

Kaz - I'd be interested to hear whether much braking is available on an NSX when the servo vacuum goes? I'm paranoid about this since the issue occurred on my student-days volvo 340 (!) and I had no capability to get the pedal down at all. Is the NSX stoppable without the servo do you know?

.....you could disconnect your vacuum pipe and try it if you really wanted to...

[m666 edd]

Cheers for all the info again.

I was soon to change the front pads and also had recently been talking to Kevin about getting the seals and pistons replaced and trying to figure what ones I needed.

I replaced the front brake pads this evening (yes Kaz I believe the pedal got slowly harder over time as I didn't really notice it) and it seems with the HiSpec brake calipers I have the outer pads wears more. The pads seem to be wearing at quite an angle so I don't know whether this means the bottom piston isn't working so well?

Here's a photo of the brake pads removed and a new set in the middle for comparision:

http://www.ripper.eclipse.co.uk/nsx/10-05-11/Brake%20pads.jpg
Far left is outer driver side pad. Far right is outer passenger pad. Top is top!

The top piston is 38.6mm and the bottom is 41.2mm which matches their current line up so I know what to buy.

Anyway after fitting these and bedding them in the pedal feels like it used to. Also as soon as I drove down the road the ABS pump activated! I was checking and poking around a lot of fuses as well but could the ABS pump have not worked because it thought the brakes hadn't been released?

Anyway glad its all working now and will flush the brake fluid and abs when I get a moment. Shame I have no spare time as I quite enjoy working on the car but really have more pressing matters with my time at the moment but of course this was an important safety issue. I may change the rear pads depending on how the week pans out.

[m666 edd]

It seems the old pads had overheated to cause the uneven wear. They were mintex 1144s which makes sense. With the brake dust they produced I thought they were 1155s which have a higher operating temp range.

[forumadmin]

It's not unsual to lock up the wheels on this particular car, as the brakes are so much more bigger than OEM. What you need to be using are the 888s, then you will know what braking is! I also guess the ABS is a bit slow to keep with the rate at which the brakes can operate. I really only ever used 1144 pads in, though I did give you some 1155's as well. The performance of the 1144 was good enough not to need to use the harder pads. I figure they would be easier on the rotors than the harder pads so stuck with them.

Also note, if the pads wear unevenly too much, they will be cocked in the caliper and might bind. Remember I said how the newer calipers have steel wear plates, probably to prevent the pads digging into the alloy caliper body.

[m666 edd]

The pump was definitely not activating beforehand though. Binding brakes causing the ABS to think the brakes are in use so the pump didn't activate maybe? When I say activate I mean pumping whilst just driving down the road etc not when breaking. Usually I find it pumps after releasing the brake coming out of the driveway.

I agree about rotor wear. Something to think about.

I could only find a set of 1155s for the rear but I've got parts stored in different places so maybe I missed it.

[forumadmin]

I think the pump, is activiated purely on lack of pressure in the 'pre-charge' system of the ABS. The is a tank which stores ABS fluid under pressure. A pressure switch will sense a low pressure and the pump recharges it. If the pressure is not brought up to normal within 30secs then the warning light will show. Braking hard enough to engage the ABS a couple of times, or even once for a few seconds will get the pump going.

Something I wanted to do is upgrade to the latest ABS unit. I would do that over any repairs to the current system.

[Kaz-kzukNA1]

Kaz - I'd be interested to hear whether much braking is available on an NSX when the servo vacuum goes? I'm paranoid about this since the issue occurred on my student-days volvo 340 (!) and I had no capability to get the pedal down at all. Is the NSX stoppable without the servo do you know?

You can slow down and eventually stop your NSX but it all depends on the conditions.


Unless suddenly something mechanically failed at the booster, you still have the vacuum assist even if you have stalled the engine and thus, you can stop the car in a similar way if you don't panic and try to press the brake pedal multiple times.


If you lost the vacuum completely, then you will need to press the pedal really hard and unless you have experienced it, you won’t understand how hard you need to be.


I’m doing this almost every day but only at the crawling speed like a snail.


In order to get enough space to work on another NSX, I always move my car out of the garage.


I hate starting the engine just for 10sec due to the blowby gas so I normally just push it out.


As my natural habit, I always press on the brake pedal several times before moving the car so I don’t have any vacuum assist when moving the car.


Even at the crawling speed, you must press on the pedal fairly hard.


If I have to do this even at 10mph, I don’t know how quickly I can stop the car….

In a simplified notion, it's the ratio between the diameter of the mater cyl VS the piston at the calliper and thus, you need to generate multiple massive pressure at the master cyl without the vacuum assist.

Kaz

[Kaz-kzukNA1]

The pump was definitely not activating beforehand though. Binding brakes causing the ABS to think the brakes are in use so the pump didn't activate maybe? When I say activate I mean pumping whilst just driving down the road etc not when breaking. Usually I find it pumps after releasing the brake coming out of the driveway.

......................................

Hi, Ed.

Unlike the OEM one, you are using aftermarket opposed piston calliper so the characteristic is quite different from what I wrote in the earlier post. Just ignore it for your case.


I have never dealt with Hi Spec calliper so I don’t know whether it has dust boot or not at the piston.


Like some of the Brembo and other models, you MUST refurbish it more frequently than the OEM ones especially some of them don’t even have the dust boot over the pistons.


Depending on the track condition, dust boot won’t survive due to excessive heat generated so not included in the original design any way.


In UK, I noticed that not just the brake pistons but also the nuts/bolts/etc seemed to get corroded at similar speed/rate to the cars based in coastal area of Japan.


On brake callipers without the dust boot, piston can easily seized if not refurbished regularly with the salt in the air.


The pad at the entry side of the calliper (top side, if the calliper is mounted at the forward section of the disc) has its own self-biting effect so in order to balance the friction level, normally you use smaller piston at the entry side.

Even with this, depending on the conditions, you will get imbalance in pad wear so it is very important to check the status regularly.


It depends on several conditions but you are probably OK to use the same brake fluid for a few track events if you are using the expensive racing brake fluid.

It would be cheaper to use the racing brake fluid than replacing the standard one after every track day if you regularly track your NSX.

This is the good time to check your pads, disc, calliper as you need to bleed both side of the callipers.


If you don’t track a lot, probably better to stay with the standard fluid and replace it after each event and check the components at that time.



Regarding the ABS, it’s pretty much the same as what forumadmin said.


ABS controller monitors the condition of the accumulator pressure switch.


If the pressure at the accumulator drops, the switch will become in OFF status.

With this signal 'AND' the first time when one of the rear wheel speed signal exceeds 10kph (6mph), the ABS pump will kick in.

This is why you don’t hear the ABS pump just after starting the engine but always hear it on leaving your driveway.


It will stop the ABS pump after about 3sec once the pressure switch becomes in ON status.


If the pressure switch doesn’t get ON status (accumulator pressure is still lower than the threshold) within 120sec after the ABS pump was activated, you will get ABS warning light.


If you exercise your ABS first thing in the morning at very low speed before the tyre warms up, the ABS pump will kick in after about 2 – 3 times you exercised it.


If it kicks in every time when you exercised it, you are very likely to have problem with the accumulator or the solenoids.


Any ABS on our NSX before the introduction of the later spec one body solution, it is highly recommended to exercise it regularly at a safe place to prevent debris trapped at the solenoids.


As you didn’t hear the ABS pump for a while, seems like you are holding the good pressure over the long period. This is a good news.


Still, best to flush the system regularly to prevent any issues.

Already saw so many different scenario/failure modes on this type of ABS….


Kaz