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Please help: Strange clutch / transmission noise

BB

Experienced Member
Joined
15 August 2000
Messages
570
Location
Bellingham, WA
Ever since I first got my '91 NSX a little over a year ago, I have occationally heard a strange clunking noise when driving really slowly in 1st or 2nd gear. It sounds like something clunking back and forth in a semi-random manner about 2 to 3 times a second.

The noise is only present when the vehicle is in gear and rolling. As soon as the clutch pedal is pressed in, the noise stops. Also, very rarely there is a single clunk noise right when you first engage the clutch.

The noise comes and goes. Some days I never hear it at all, even if I try to force the noise to happen. Other days it happens constantly. The car being warm or cold seems to have no effect on the noise.

The easiest way to force the noise to happen is by driving very slowly in 1st gear, then suddenly giving the car a slight burst of gas, then QUICKLY let off the accellerator pedal while reamining in first gear. Doing that usually starts the clackity noise for at least a couple seconds if not longer.

Likewise, when the noise appears if you give the car a bit of gas, the noise goes away. And as mentioned above, pressing in the clutch pedal does the same thing.

At first I thought this was a problem with my clutch and since I planned to have a new clutch installed I didn't worry about it. Now just 2 weeks ago I had the Comptech PG2 clutch installed and the problem appears to have become worse! I'm surprised the dealer didn't notice it, but considering how the noise comes and goes it's believable they never heard it.

Does anyone have any idea what this noise might be caused by? I have read everything I could find on the net and came up with the following possibilities: Throwout bearing on the clutch (lack of grease), noisy bearing inside the tansmission, common problem on NSX's--don't worry about it.

Did the dealer screw up when they installed my new clutch, or does this problem have nothing to do with the clutch? In Comptech's installation instructions it mentions repeatedly in bold type to apply only Honda Hi-Temp grease on a number of parts. The dealer charged me for washers, fluids, and every other trival item used to change-out my clutch, yet Honda Hi-Temp grease isn't listed anywhere. Makes you wonder doesn't it?

Finally, when the noise is present it in no way affects the way the clutch engages or the car drives. It's just very annoying an embarassing sounding. Please help!!



[This message has been edited by BB (edited 31 October 2001).]
 
You can rule out the throwout bearing. It is only used when the clutch pedal is pressed in. (BTW, generally a good idea to replace it when doing a clutch if the old one has a lot of miles on it.)

It sounds more like half shafts. Try rolling slowly in 1st, and get on and off the throttle several times lightly but quickly. Does it clunk as you get both on and off? If so, it could be the shafts or some play elsewhere in the trans-axle. You might be able to find it by jacking up the rear and have some one twist one wheel back and forth as you do the other. Might be other possibilities, but that's the first thing that comes to mind. Do you hear anything when you first apply the brakes?
 
I think what you are hearing is the differential engaging (but I could be wrong). Every NSX I've ever driven does this. In a parking lot, you can replicate this with the clutch in, and cruising at about 10mph. Press lightly on the gas, and then get off real quick. I think you'll hear the "clunk" noise then.

-- Chris

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Originally posted by ScienceofSpeed:
I think what you are hearing is the differential engaging (but I could be wrong). Every NSX I've ever driven does this. In a parking lot, you can replicate this with the clutch in, and cruising at about 10mph. Press lightly on the gas, and then get off real quick. I think you'll hear the "clunk" noise then.

Chris: Yes, doing that will often cause the clunk noise. Except rarely is it just a single clunk noise. What you hear is a clunking sound several times a second as if someone was rattling something back and forth-- 5 or more of these noises in a row sometimes.

sjs: I'm not sure if it does it when getting both on and off the accelerator. If I recall correctly it's only when I get off the accelerator, but I could be wrong. I'll have to go check and see.


[This message has been edited by BB (edited 01 November 2001).]
 
Actually, it will be simpler to test in second gear, but at very low first gear speeds, say 5 MPH. I think what Chris describes is the same thing I chalk up to general play within the transaxel. I'm not sure exactly where it is or how much is "normal".
 
I agree with Chris, you are hearing the differential noise. Try this, jack up your car so BOTH rear wheels are off the ground.
Then try turning one of the wheels by hand and apply pressure, and then release several times. You will get the same clacking noise that I think you are hearing. Basically when you let out the clutch at low speeds, you get a little backlash from the engine which translates to an on/off force (small) on the wheels. This causes the differential to lock and unlock which is the noise you are hearing (I think).
 
I had my tranny fluid replaced yesterday and heard a strange noise when shifting into drive. I took my Father's advice and turned up the radio.
 
Edo,

Thanks. That's good to know there's probably nothing wrong. Although I'm still a little worried.

Why would the NSX be so noisy in this regard, yet on 3 other Hondas I have owned (all with manual transmissions) they have never made this kind of noise? I even went and attempted to make my CRX make a similar noise, and I couldn't reproduce it there either-- it's just smooth and quiet.
 
The CRX doesnt have a limited slip differential does it? If it doesn't it wouldnt make the sound. That and if it DOES have one, the engagement is probably quite a bit less strong. The NSX has a very stiff differential compared to say something like a CRX.
I heard some BMW guys complaining about the same thing on their M3's..
 
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