Grinding sound while idling, any ideas?

[gsarmed]

Hello folks. While my 2004 S2000 is idling with the clutch pedal out and in neutral, there is a loud and distinct grinding sound. When the pedal is pushed in, the sound decreases almost to the point where it is gone altogether. Any ideas what may be causing this? Thanks.

[repiv]

Sounds and noises are extremely hard to describe in words, but let's look at what we're dealing with here.
The difference between clutch in and clutch out while in neutral is in the former, the engine is disconnected from everything downstream of it. When the clutch is out (or engaged), the engine is spinning the clutch disc and thus, the transmission, but the transmission is not spinning anything downstream of it. The noise must therefore, be coming from the clutch disc or the transmission. Can you detect this grinding when you drive the car very slowly (since you say you can hear it at idle) in first or second gear and does it continue to make noise as you gradually speed up? Have all noise making devices turned off (stereo, fan, etc) and have the top up and windows up to keep out wind and road noise. Once you get a speed that makes the noise, push in the clutch and coast. Does the sound go away? If it does, then the noise is likely confined to the clutch disc because, now, your rear wheels are spinning the tranny. Your clutch disc could be badly worn, warped, broken or have broken springs or spring retainers.
If the noise stays, it's likely some part of the tranny (perhaps one of the bearings). The rear bearing on the tranny has been known to go bad and make noise.
I would suggest you check the fluid level in the tranny. This will be difficult to determine just where the level actually is, but you can do a test to approximate it. You can jack it up from the left side, crawl under and remove the fill bolt. At this point, you could stick you finger in the hole to see if you can feel for where the fluid is, but since it's jacked up, you may not reach it. (If you can put it on a whole car lift and remove the fill plug, this would be best.) Assuming you don't have a whole car lift, then drop it back down onto the ground after you put a shallow catch pan under the fill hole. Do you see anything dribbling out? If not, go jack it up from the other side and monitor when the fluid begins to dribble out. Stop when it starts to come out. It shouldn't have to go too high before fluid comes out. If you must jack it up a lot, then you are very low on fluid. You may as well do a tranny fluid change while you're at it. The fluid should be right at the bottom of the fill hole when the car is on level ground.

[SXY_S2K]

Throwout Bearing...

[repiv]

I considered the TO bearing (and it still could be a possibility) but he said it makes the noise when the clutch is engaged (ie, pedal up). When it's engaged, the TO bearing is under almost no strain or load. If he had said it grinds when the clutch pedal is on the floor (clutch disengaged), then I would be more inclined to say the TO bearing.

[RatedR]

I have the same problem, but mine's not as loud, and it goes away after warm up. I'll try to change my tranny fluid soon so I can check for shards. I'll let you know what happens....

[gsarmed]

Thanks for the responses. BTW, here is some more info. it is 100% stock. I bought it 1 year ago w/6k miles on it from an older guy one street over that babied it since he bought it new. I first noticed the noise at 7k miles and it has not gotten better or worse since then. It It now has 15k miles on it and although I drive it hard and to the redline at every opportunity, it has never been abused. Below are the answers to the ?'s above:

"Can you detect this grinding when you drive the car very slowly (since you say you can hear it at idle) in first or second gear and does it continue to make noise as you gradually speed up?"
No I have tried but I can't over the engine noise.

"Have all noise making devices turned off (stereo, fan, etc) and have the top up and windows up to keep out wind and road noise?"
Yes I hear it when the top and windows are up and radio off. It's difficult to detect with the top down.

"Once you get a speed that makes the noise, push in the clutch and coast. Does the sound go away?"
I can't hear the noise once under way. I tried what you suggested but it's quiet while coasting..

I do know that the tranny fluid is the same it left the factory with and none has leaked out etc. I guess it is possible that it left the factory low but it's not likely. It is a vexing problem.......

Thanks for the thorough analysis. It's appreciated. Please let me know if anything else comes to mind.

[repiv]

"Can you detect this grinding when you drive the car very slowly (since you say you can hear it at idle) in first or second gear and does it continue to make noise as you gradually speed up?"
No I have tried but I can't over the engine noise.

OK, here's where I'm having a problem with this whole situation. Your first post you said:
there is a loud and distinct grinding sound

I wish to now reiterate my first statement about describing sound over the internet. I'd now like to add that it's also a personal interpretation of what "loud" means. If this noise is indeed "loud", then it should be heard while the car is being driven slowly. The fact that even driving the slowest speed drowns out this noise, tells me that it is nothing to worry about. I now believe that what you're hearing is normal, typical tranny gear noise as the tranny is spinning around. I have personally diagnosed several cars where new owners think something is wrong when they hear this noise. Upon close examination, it was found this noise is NOT anything abnormal. The transmission contains a lot of spinning gears and shafts. This car has much less sound insulation than any other production car on the road. Those normal sounds simply come through.
If you are still worried about it, find some other S2000s in your area (go to your regional forum and arrange a meet with some of them) and compare. In the meantime, check your tranny fluid level for peace of mind. You've got 15K miles on it. Although Honda says you don't need to do anything with the tranny fluid for a very long time, you may as well change it to their current, new and improved MTF. That too, will give you some peace of mind and it seems to me that right now, that is mostly what you need.

[gsarmed]

Thanks for the feedback. I completely realize it is hard to diagnose anything noise related over the internet and thanks for the effort. A little more info if it helps. The noise is not present when the car is cold. Not at all. It manifests itself after the car is warmed up. My commute is 30 mins and I notice it when I park at work and put the top up. There are 3 degrees of the noise. It is loud (again a grinding noise) when I am idling in neutral with the clutch out. The noise diminishes greatly when I push the clutch in. After the clutch is in and I shift into first (or any gear for that matter) the noise goes away completely. When I take the car out of gear the grinding noise resumes.

[ajay]

I'm not going to attempt to add tecnichal input here, but are you still in you 3yr warranty period?

[repiv]

The noise is not present when the car is cold.It's obviously heat related. Again, check the fluid. It may still be a normal sound.

After the clutch is in and I shift into first (or any gear for that matter) the noise goes away completely.
As I explained earlier, when you do this, you have effectively stopped the tranny from spinning. No spinning, no gear noise. Again, I can only suggest you check and/or replace your tranny fluid. Other than what I've already suggested, there is not much else I can tell you to do. You need to act upon the recommendations I've already made. Till you check the fluid level at the very least and perhaps compare sounds with another S2000, nothing more can be accomplished on the net.

[oakfloor]

Hello folks. While my 2004 S2000 is idling with the clutch pedal out and in neutral, there is a loud and distinct grinding sound. When the pedal is pushed in, the sound decreases almost to the point where it is gone altogether. Any ideas what may be causing this? Thanks.
This may be the rear tranny bearings going out, as they are at the end of the oil supply, and gaul. I have a MY '00 and it make a grinding noise also. take a sample of the tranny oil and have a UOA . I thought that honda has fixed this on later models? How many miles on it?