What Actually Causes the "Clack, Clack, Clack" Noise in our Transmissions?

[Mac Attack]

New NSX owners routinely ask if the clunking, clicking, or clacking sounds in our drivetrain are normal, and we tell them it is.

Recently, I installed a carbon fiber clutch that is on/off and shudders very violently when trying to get it going from a standstill. It will be removed shortly. Our drivetrain clunking noises compounds this unpleasant experience and makes this thing embarrassing to drive around town while the clutch is shuddering away from a stoplight or stop sign.

I've never personally taken apart one of our manual transmissions, but that may change here soon.

Does anyone know if there is specifically something inside the transmission that contributes to our noises? I don't think it is the driveshafts or intermediate shaft. It seems like too much "slop" in the gears like the gear mesh isn't tight enough. In that case, I can't do anything about it.

But, not knowing much about these transmissions, I'm hoping there might be something I can do to make it a bit better when I open it up.

Thanks,

Dave

 

[NSX9]

A few years ago we had a drive in Tasmania Australia and were very privledged to have a guest from Japan, Mr NSX, Uehara Shigeru. He drove some of our cars and when he drove mine for a few hours, his control and smoothness was outstanding. As we were coming into a city and he was just idling along the car did the trans shudder as above, he just looked at me and said......normal. So I guess that makes it OK, still not sure what causes it but play in the gear train while not under load seems reasonable.

 

[davidf]

A few years ago we had a drive in Tasmania Australia and were very privledged to have a guest from Japan, Mr NSX, Uehara Shigeru. He drove some of our cars and when he drove mine for a few hours, his control and smoothness was outstanding. As we were coming into a city and he was just idling along the car did the trans shudder as above, he just looked at me and said......normal. So I guess that makes it OK, still not sure what causes it but play in the gear train while not under load seems reasonable.

Thats a pretty neat story.

 

[Old Guy]

Probably due to gear lash or 'slop' if you are inclined to a less technical term. All gears will have some clearance between the teeth face. This clearance materializes itself as a little bit of lost motion until the teeth come into contact (the clunk). Some of the clearance is designed in and some of it is due to manufacturing tolerance and then there is wear. The designed in lash includes clearance for lubrication and perhaps accommodating differential heating expansion in the gears. As such, it is impractical to have zero lash gears. Honda may have designed more clearance into the gears to accommodate the lubricating film and heat - that would be speculation on my part.

I seem to recall from a 2nd year engineering lab that lash increases between a gear pair when the gear pair has a greater base circle mismatch, such as in first gear. However, that lab was in a previous century and it was a class for mechanical engineers and I am electrical so I probably wasn't really paying attention. Can't remember why I was there either.

 

[Mac Attack]

That is a neat story NSX9. It's something that all NSXs have, but it still drives me nuts. Especially with this clutch jerking everything around the way it does.

Old Guy - It has to be the loose gear mesh as we've both identified, but I was curious if it is due to the differential in particular or something else I could change.

I wonder if those that have changed their differentials to aftermarket ones have noticed any reduced drivetrain lash? They typically run heavier weight oil at the same time, so that may also help.


It's one of those things everyone notices when they hop in the NSX - why does it sound like the drivetrain is about to fall out of the car? It doesn't need to be like this.

I guess after 11 years it is probably my biggest complaint with this car.

Dave

 

[ralph cerbone]

How many miles on the car , how did you determine the drive shafts were not the problem .

 

[BamaFan]

Was this just an issue with earlier cars? This does not happen at all on my '95. These cars received a revised gearbox with a different ratio for 2nd gear and a new differential that increases cornering speeds. Perhaps that addressed the issue? Or is my NSX just unusual?

 

[Old Guy]

My 2000 has the same drivetrain lash issue. I originally thought that the drive shafts must be worn. I pulled off the wheels and inspected the shafts. Nice and tight with no perceptible rotational play. A little web search at the time revealed that it was a common phenomena and not a sign of imminent failure.

The NSX has, compared to other cars that I have driven, a fairly narrow engagement point on its OEM clutch. That might be great for quick shifting; but, certainly contributes to stop and go driving agony when mixed with the drivetrain play. The thought of driving in urban traffic with a more aggressive clutch leaves me cold. I suspect that the reports of people using up their clutch in less than 40,000 km is probably due to a strategy of revving the engine and slipping the clutch to get a smooth take off from a stop.

I would not expect that the heavier weight oil in aftermarket differentials would make a material difference to the clunk unless that heavier weight was due to the old used car salesman's trick of adding sawdust to the transmission oil to (briefly) quieten the gears:smile:.

 

[Jinks]

My Oem clutch always clanks and makes noises when doing an intial take off when cold. I am wondering if this is the same issue as being described here, or is this issue something different? Maybe I should check the motor mounts?

 

[Old Guy]

My Oem clutch always clanks and makes noises when doing an intial take off when cold. I am wondering if this is the same issue as being described here, or is this issue something different? Maybe I should check the motor mounts?

If the noise is only present when cold and disappears at higher temperatures, I don't think that is a motor mount issue.

The 'slop' in my car's drivetrain is pretty much present at any temperature. It is most noticeable in first gear at low speeds. In the higher gears it is not an issue.

 

[clean_green]

My '02 makes a clank noise but only when going in reverse. I've always wondered what's up with that. It seems awfully unrefined in such a precision car.

 

[goldNSX]

The most common and prevalent noise you get from an NSX tranny is due to the countershaft moving inside the box. Normal.

 

[skafia]

I've owned a 1991, 1999, 2000, 2002, and 2005 and they have all made this beautiful noise.

 

[davidf]

The next time the back wheels are up off the ground, grab a wheel and rock it back and fourth a few times. You'll nearly sh!t.:wink:

 

[Mac Attack]

How many miles on the car , how did you determine the drive shafts were not the problem .

Currently ~125k. I've owned it since it had 60k miles on the OD. Driveshafts aren't the issue as I had them apart recently for a rebuild with Redline CV-2 grease. They are still tight.

- - - Updated - - -

Was this just an issue with earlier cars? This does not happen at all on my '95. These cars received a revised gearbox with a different ratio for 2nd gear and a new differential that increases cornering speeds. Perhaps that addressed the issue? Or is my NSX just unusual?

No, it's pretty much all of them (see posts below). Yours might be a special one :smile:. Does it have the JDM gears? Aftermarket differential? What oil are you using?

- - - Updated - - -

The thought of driving in urban traffic with a more aggressive clutch leaves me cold.

The nice thing about the carbon clutches is the light pressure plate. The torque capacity is due to the very high coefficient of friction. The RPS carbon pedal pressure feels like OEM. Just mine seems to have excessive shudder and I can't stand taking off from a complete stop. Once it's rolling it's excellent.

- - - Updated - - -

The most common and prevalent noise you get from an NSX tranny is due to the countershaft moving inside the box. Normal.

The transmission is the one thing I've never personally disassembled on my car. Looking at the SM it looks like there are different thrust washers and spacer collars you can order for the gears on the countershaft. I'm also contemplating the JDM gears if I take it apart. It's always been something I wanted to try.

 

[Old Guy]

The nice thing about the carbon clutches is the light pressure plate. The torque capacity is due to the very high coefficient of friction. The RPS carbon pedal pressure feels like OEM. Just mine seems to have excessive shudder and I can't stand taking off from a complete stop. Once it's rolling it's excellent.

Its not the high pedal pressure that would make stop and go driving a hassle. Its the fact that performance clutches typically come with a very narrow engagement point which makes a smooth take-off difficult.

 

[Jinks]

Its not the high pedal pressure that would make stop and go driving a hassle. Its the fact that performance clutches typically come with a very narrow engagement point which makes a smooth take-off difficult.

Exactly the same issue with my previous CT power grip 2 clutch. I miss it so much. But yet I do not... It was on the car when I purchased it in L.A. Then drove 375 miles through heavy traffic up to the San Francisco area in the middle of July. During a 115 degree heat wave. Just feathering the clutch at a dig would light up the whole rear end, even before going supercharged.
I must say, I enjoyed every minute of it.... But there is no "in between" running that clutch in my opinion. With an Oem twin disk clutch and a not running a supercharger, I could feather the clutch to smoothly take off, or I can just dump it and get the car sideways as I would normally takeoff with a aftermarket clutch that grabs instantaneously. Clutches are subjective I think. But after market clutches come with a lot of downsides in my own personal opinion.
After going supercharged, I miss the CT clutch a whole lot. Until,,,, I get stuck in traffic.... Then the choice becomes very clear... Even still, I might buy another one.:biggrin:

 

[Old Guy]

After going supercharged, I miss the CT clutch a whole lot. Until,,,, I get stuck in traffic.... Then the choice becomes very clear... Even still, I might buy another one.:biggrin:[/QUOTE]

The on / off nature of a performance clutch might have its entertainment value - unless you embed yourself in the back end of the slow moving Camry in front of you :smile: . The other down side to the narrow friction point is that the wider engagement point on the OEM clutch eases the shock load on the rest of drivetrain. If you have a performance clutch and drive a lot in urban traffic, that increased shock loading will probably take a long term toll in parts failure. If you spend your life on the race track, stop and go is not a big part of the repertoire so the shock load from the narrow friction point is not going to be a deciding factor.

 

[BamaFan]

No, it's pretty much all of them (see posts below). Yours might be a special one :smile:. Does it have the JDM gears? Aftermarket differential? What oil are you using?


Mine is 100% stock. In its 124k miles it has had the clutch replaced once (at 90k) and the clutch master cylinder replaced twice. It sometimes takes some wiggling to get it in reverse when it is cold, but nothing else of note.

I have it at Source1 right now to get some servicing done and have asked them to change the fluid as a matter of routine maintenance to see if that helps with the recalcitrant reverse gear. They are using their custom fluid mix. Hope that doesn't make it "clunk"!

 

[BamaFan]

Wanted to update this with a couple of things;

1) Got my car back from Source1, where they changed the transmission fluid (among other things). I am amazed by the difference their blend made. I have always had to rev and jiggle it a bit to get it in reverse when it first started up. Now it slides right in with no effort. I highly recommend the switch if you have not done it yet.

2) I knew that the transmission was updated in 1995 with a shorter 2nd gear for faster acceleration to make up for the added weight of the targa, but I recently read (on BaT) that it was also tweaked in '94 to reduce transmission noise. But that does not explain why some on here write about noise on later models.