Question for Kaz - Drive shaft clunk!

[Papalazarou]

Hi Kaz,

great to meet you at Japfest. I was wondering whether you could explain to everyone why most NSX's suffer from the clunking noise from the drive shafts in low gears in stop start situations?
I was also wondering whether you could explain why it is that many cars also snick into second when they are cold?

I think many of us have wondered about these quirks and it would be great to have a definitive explanation.

Thanks,

James.

[Sudesh]

Good question James! Always wondered that myself and thought the noise was the clutch more than the drive.

[Kaz-kzukNA1]

Hi, James.

Good to hear from you and yes, it was great meeting you and other members at the Japfest.

The simple answer for your 2 questions is the combination of mechanical design, lubrication technology, torque transfer and operating environment.

For the notchy/stiff feeling on shifting to the 2nd gear when the MT oil is cold, I wrote the following post last year for the different question (NSX Differential) so please refer to this;

Just a note on the transmission oil.

..... as NSX has quite small oil capacity considering its performance ....
Only 2.8L for such a high performance car (on MT, rev limit starts at 8,000rpm:)). This is really small compared to other high performance sport cars.

As this post is for the NSX differential (DF), I don’t want to go too much in detail but...

..... with the ingenious way of circulating the oil for the mechanical parts inside the GBox, the MTF needs to be looked after very well.
If you have a chance to look at the inside of the gbox, there are hollow section on the main, counter and reverse shaft. There is a meshed strainer (filter) and standard impeller type oil pump. This pump is driven by the DF. Yes, it’s by the DF and that means, the oil won’t be pumped around the gbox until the car has started to move.
In order to provide the mechanical parts with enough oil using such a small oil capacity under high rpm, the oil is actually pumped through inside the hollow section of the main, counter, reverse shaft and the passage on the gbox case.
Because of this design, the transmission oil for NSX requires soft viscosity with strong oil film. In fact, when NSX was first introduced to the market, it was recommending 10W-30 Eng Oil (quite soft) or Honda MTF as the transmission oil. I have the Honda MTF-3 and other aftermarket transmission oils in my garage. Compared to these other brands, you will be surprised to see how soft the Honda MTF is even in the cold winter. It dances like a water (may be too exaggerated...) inside the container.
So, if you put high viscosity transmission oil on NSX (like some of my friends), then quite often, you’ll notice notchy/stiff feeling on 1st/2nd gear on cold winter morning. On leaving the garage, you won’t notice it because the DF is not moving and thus no hard oil is delivered to any part of the gbox. Once you started to move, the DF/pump would try to circulate the very cold and hard oil causing the notchy/stiff shift. Eventually, the heat from the engine will be transferred to the gbox case and the rotating gears will raise the transmission oil temperature and thus, no more nothcy/stiff feeling. Obviouly, this is presuming that you don't have any mechanical failure as transmission oil won't be able to cure it.

So, unless you track the car, it is recommended to use Honda MTF-3 (I think this is the latest version) for your transmission oil. It is a very good and thought after oil. You can easily get it from your local Honda dealer. If you use your NSX on the track, depending on the shape of the track and the temperature, you may notice changes in shift/DF feeling within a short period... It’s getting too hot :eek:and thus you may want to search for the aftermarket oil with the trade off of nochy/stiff feeling in the winter.

Regrds,
Kaz

Addition to this, the 1-2 synchro hub & sleeve are on the counter shaft whereas the rest (3-4 and 5 for 5MT, 3-4 and 5-6 for 6MT) of them are on the main shaft.
Beacause of this and the gear ratio of 3.071 (1st) compared to rest of the gears (about 0.7 - 1.9), you are already loosing the synchro capacity even before moving the shift folk. This is why it is common to use larger capacity on the 2nd synchro but still, you'll need extra force to get into 2nd gear compared to others.


Regarding the drive shaft...
While the engine is the source of the power, the tiny amount of the rubber on the tyre is being used to move our NSX. The tyre/wheel moves in all direction continuously whereas you don’t want your engine to move like that. So, you need some sort of flexible mechanism to transfer the engine rotational power to the tyre. Hence, the presence of drive shaft.

As in above, the joint of the drive shaft needs to cope with huge torque from the engine and at the same time, continuously move in all direction without loosing too much power and also prevent it from being damaged. Because of this, there is the roller mechanism used inside the joint and inner and outer joint roller/spider is being offset.
In order to cope with this continuous high speed movement and high pressure on the roller/spider surface, the joint is filled with special grease.
When it is new, it is like very-very sticky custard cream colour…
Due to the excessive internal movement, heat, ageing and etc, eventually, the grease will loose its performance and starting to get very soft. The colour of the grease changes to grey and starting to make noise when the roller moves inside the joint. Because the grease is getting soft, you will see grey grease leaking from the side of the rubber boot even the boot itself was fine.
For NSX with aftermarket header/exhaust, the leakage/damage at the drive shaft boot is quite common especially on the right side. At the early stage of the leakage, you may not notice it as it is not easy to inspect with the heatshield cover around the half of the joint.
If you keep ignoring the initial leakage or the tear on the boot, you’ll start damaging the roller and the spider. Then, you’ll damage the spline on the shaft itself and you don’t want to end up with replacing the entire shaft assy as it is super expensive.
It all depends on the driving condition but on my NSX, I replace all the grease/boot/etc at about every 25k - 30k miles.

I bought complete new set of MT drive shafts a while ago to refurbish the used one in order to speed up the service time. Also, I couldn't find reliable refurbished parts for this in UK. Even in Japan or US, sometimes, I noticed that the offset of the spider position between the inner and outer joint was not correct on the refurbished one so I decided to reufrbish it by myself. The length of the left side drive shaft is different between AT and MT.
5591 5590 5592

This noise is different from the clutch one. I check this during my NSX Health check service for the members and you just need to experience it. You’ll be surprised with the difference between each NSX in the feedback feeling. Obviously, on AT, you’ll get the same drive shaft noise and yet there is no noise from the clutch.

I’ll be refurbishing the drive shaft very soon for one of the member here. I’m just waiting for the part delivery so I’ll try to take several photos for you. Having said this, I won't be able to touch my camera during the cleaning process. You get so much grease on your hands/arm/cloths.... Can't wait...

Regards,
Kaz

[Papalazarou]

Thanks Kaz,

great explanation. This seems like perhaps one of the most important but overlooked parts of the service for the NSX. This is definately something I'll be getting done soon.

Kaz, do you have a price and estimated lead time for this service? I guess it would depend on whether the drive shafts need refurbing or not?

With reference to the gearbox; how available is the MTF3? I've tried to locate it in the UK but with no success.


Thanks again,

Cheers,

James.

[Sudesh]

With reference to the gearbox; how available is the MTF3? I've tried to locate it in the UK but with no success.

James I got MTF3 from my local Honda dealer no problem! They said they only sell it now in the large container, but they were nice enough to fill an old container for me with about 5liters of MTF3 for free!!

http://i77.photobucket.com/albums/j77/icongroup/NSX/DSC01623.jpg

[Papalazarou]

James I got MTF3 from my local Honda dealer no problem! They said they only sell it now in the large container, but they were nice enough to fill an old container for me with about 5liters of MTF3 for free!!

http://i77.photobucket.com/albums/j77/icongroup/NSX/DSC01623.jpg



Cool, I'll ask my local dealer again.


Cheers,


James.

[Sudesh]

This noise is different from the clutch one. I check this during my NSX Health check service for the members and you just need to experience it.

So is there 2 types of clunking noise?

I only ever hear mine clunk from time to time, when moving off from stand still, however with a few revs and bit of clutch control there is no clunking noise? Would the noise I'm hearing be the clutch?

[Papalazarou]

So is there 2 types of clunking noise?

I only ever hear mine clunk from time to time, when moving off from stand still, however with a few revs and bit of clutch control there is no clunking noise? Would the noise I'm hearing be the clutch?

Are you refering to the death rattle? The one wheere you push in the clutch and you get a short rattle?


Cheers,


James.

[Kaz-kzukNA1]

Hi, Sudesh and James.

You can get MTF-III from your local Honda dealer/garage. They are normaly suppiled in 25L tank but as Sudesh mentioned, you can just ask them to fill up your empty container. 3.0L is enough for 1 car. I think it was about GBP7.00/L +VAT...

Describing the noise is not easy even you record it on any media... Each person has different way of explaining the sound/noise. On top of this, each language has different expression on the sound. In English, 'bowwow' for the dog but in Japanese, it's 'wan wan'. 'Mew', 'miaow', 'miaou' for the cat but in Japanese, it's 'nya- nya-'.
So, we may be talking completely different sound.

The best way to understand the driveshaft noise (or any noises) is to look at the design and structure of the parts. There are 4 joints on our NSX and each joint contains spider and 3 rollers. Each roller consists of another roller bearing and eyelet and it slides inside of the joint housing. It's easier to understand by looking at the photo than expaling in the text so I'll try to take some photos.

Any way, because of these parts involved inside the joint, if the grease gets old and too soft, it will start making some mechanical noise when you rotate the shaft. If your boot was damaged and lost the grease, then that could result in an expensive repair.

As I'll be receiving the parts from Japan tomorrow, I hope I can take several photos during the refurbishment of the driveshaft.

Regards,
Kaz