I experience some noise ('clunk') when driving in first three gears at low revs. Especially in first gear it is noticeable, if I let the throttle off, and revs fall under 2000 rpm. First the car decelerates as supposed to ( engine brakes ), but then suddenly the engine seems to release the brakes causing deceleration, and at that point car make some clunk or clack, possibly twice. Sometimes same clunk is noticeable, when the car decelerates in first, and then i suddenly clutch and break. Sometimes this happens when I release the clutch when I drive off...

Some my friends addressed this problem as a differential airness or differential mounting airness ( I don't know the exact expression, what in my language call airness - like there is too much tolerance, too much air... )...

Can anyone explain if this is normal ( I suspect not ), what could be causing this noise and what should I tell service guy to look for ( the car is under warranty, 2000/03 )...


Thanx in advance!

 

"Drive line slack". If you are attempting to drive the car at a steady state below 2000 rpm, you are probably getting this back and forth "thumping" when the revs get too low (close to idle) and the ECU tries to compensate by increasing the revs. It's almost like you are trying the accelerate then decelerate repeated except that the computer is trying to do it for you as it tries to stabilize the idle. Throughout your drive train, there are little gaps (or spaces) between the gear teeth that get closed up when you apply power, then when the power is removed, all those little gaps get closed in the other direction. Have you ever watched and listened to a long freight train in the yard as it's trying to move slightly ahead? All those couplings between each car take up the slack and go "bang" and when the train engine stops, all those couplings go "bang" again when each car "runs" into each other. Your vehicle's drive line is sort of like this but is more noticeable when you are going slow. At higher speeds, those gaps open and close so fast you don't detect it as much.
If you are worried about it, have the tech check it out but I think it's normal given what you just described.
Also, if you tried to accelerate too quickly with the clutch always in and the revs are near idle in 1st gear, especially when the engine is hot, you'll get the often reported "bucking" or "kangarooing". These too, are normal and can be resolved by using your clutch more at low speeds. Kangarooing is just the next level from what you are reporting here.

 

xviper:
Thank you very much for such a fast reply.

I understand everything you wrote and this is what I had been imaging and what others had told me to be. And as far as I understand, this is the case with every car, not unly s2k. But with s2k, it is very noticeable - louder than in other cars.
It sounds as when other cars, as they get too much diff gap or diff mounting rubber becomes inefficent <- that's what a friend told me was the case with his 300zx.

So since I'm second owner and the warranty last only 3 months more, I'm worried this is not normal and suspect that it was not the case with the new car. I've also been codriver in another s2k, and this problem was much less obvous. If you have your car since beginning please let me know if this was or was not the case with new car.

Thank you very much!

 

Yes, I have owned my car since new. It is just over 2 years old. I have not noticed any change in this characteristic and it is not one that I'm concerned about.
However, since your warranty is about to end and you are not the first owner, there may be things about the car's history that you do not know about. I usually recommend people in your position to have the car get a complete and thorough mechanical and safety inspection. Then take the car to the dealer and ask that any warranty items be fixed. Once the warranty is up, you are on your own and repairs on this car can be very expensive.