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:


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.