Drivetrain noise at 4100 rpm? - LotusTalk - The Lotus Cars Community
 
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post #1 of 10 (permalink) Old 10-26-2014, 06:27 PM Thread Starter
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Drivetrain noise at 4100 rpm?

After installing the ACT clutch and Comp flywheel a few months ago, we have since developed a strange, worrisome noise that we need help diagnosing. It started about 3 months after installing the clutch and flywheel, with no problems until this point.
No problems noted in driveablility at all. Car works fine and is awesome!

So we now have a higher frequency buzz/rattle which starts intermittently around 3500, resonates at 4100 rpm and diminishes around 4500, like marbles in a small can. It is coming from the engine compartment, behind the driver's seat. Does not occur at idle, when coasting in neutral, or revving engine without clutch engaged.

It only occurs when moving, clutch engaged, under steady light load, maintaining speed, in any gear. Speed variation does not affect it, only throttle modulation and depressing the clutch. It is always at 4100 rpm! I tried jiggling the gear shifter and feathering the clutch, no changes.
On hard acceleration, no noise all the way to redline!

What could it be? I don't think it is a wheel bearing, or CV joint. Do not think it's the differential or transmission. Could this be a defective clutch plate or maybe the little plastic clutch tool centering ring that we had to leave behind the flywheel coming loose?

Appreciate any advice on how to figure this one out.
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post #2 of 10 (permalink) Old 10-26-2014, 07:56 PM
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I believe those are the syncros. Mine did the same thing after installing a fidanza flywheel and ACT clutch, but the noises were not very noticeable.

2006 Elise ST (someone else has it now . . . )
2008 Exige S240 ST
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post #3 of 10 (permalink) Old 10-27-2014, 01:48 PM Thread Starter
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Doh!!!

Loose front motor mount frame bolts!
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post #4 of 10 (permalink) Old 10-27-2014, 02:04 PM
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Originally Posted by ///MD View Post
Doh!!!



Loose front motor mount frame bolts!

I got mine back from a shop once and it had picked up a nasty rattle. I had to take it right back to them for some other stuff, and they quickly found a bolt resting on top of the undertray. It's always nice when it is simple like that!


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post #5 of 10 (permalink) Old 10-27-2014, 05:12 PM
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Originally Posted by ///MD View Post
Doh!!!

Loose front motor mount frame bolts!
That's easy.

I was gonna say throwout bearing, since it only made noise when you pushed in the clutch. Helped a friend replace his new ACT throwout bearing after only 500 miles... It was destroyed!

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post #6 of 10 (permalink) Old 10-27-2014, 10:25 PM
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lucky guy.

I too have ACT clutch and Fidanza flywheel. Anyone has that whirling sound while driving normally? Usually you hear it on declaration.

** save ~10 lbs gain 1 hp ** EQ: Y=(190*X) / (1984-X) where Y is (HP) and X is (lbs)

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post #7 of 10 (permalink) Old 10-28-2014, 03:35 AM
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...Usually you hear it on declaration.
^Which is why lawyers always recommend not uttering even a single word.^

Or it sounds like the case is being thrown out, bearing...
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post #8 of 10 (permalink) Old 10-28-2014, 05:27 AM
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Originally Posted by ///MD View Post
Doh!!!

Loose front motor mount frame bolts!
Guess I'm taking off my diffuser for the 3rd time this week to check that. I have the EXACT same rattle/buzz that has started in the past few weeks. I checked the actual motor mount bolts themselves, but not the frame bolts I don't think...

I'm also thinking it's my exhaust. Hard to say.
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post #9 of 10 (permalink) Old 10-28-2014, 09:51 PM
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^Which is why lawyers always recommend not uttering even a single word.^

Or it sounds like the case is being thrown out, bearing...
That's the only time I can hear since the exhaust is so loud. I haven't driven the car in 3 weeks and won't for at least another 2. Broken exhaust hanger and smog check.

In fact, I don't even remember if the stock clutch & fly made that whirling sound. I don't think it did. I can watch some old video I took from inside the car, to be sure.

** save ~10 lbs gain 1 hp ** EQ: Y=(190*X) / (1984-X) where Y is (HP) and X is (lbs)

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post #10 of 10 (permalink) Old 10-29-2014, 06:38 AM
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Push your shifter to the side while driving and see if this reduces the noise. If so, it's a harmonic imbalance in the shift linkage. There are multiple threads on this.


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