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"Fluttering" Under Load (Read 1234 times)
OK-944
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"Fluttering" Under Load
Aug 13th, 2019 at 2:59pm
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Well maintained 1987 NA with 165K miles: While driving under some load...like a medium uphill grade in 5th gear with engine at around 3K rpm's - I can feel a slight "fluttering," like something is just a bit out of balance. 

Hard to say exactly where this is coming from - but definitely not from the rear of the car.  More like either directly underneath the gearshift, or forward towards the back of the engine.

Balance shaft timing checks out ok - so my thought is that this is a torque-tube issue.  As in it may be time to address the TT bearings.  Then again - perhaps this an early sign of a main bearing issue?

Oil pressure has always been good.  All other gauge readings fine and consistent.

Any ideas?  Thanks!
  
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johnstahl
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Re: "Fluttering" Under Load
Reply #1 - Aug 14th, 2019 at 1:42am
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I would think the TT bearings would make more of a bearing wearing out sound, more of a grinding. So my guess is a clutch issue. Could be caused by a rear seal issue (oil on clutch).

"Fluttering" is this a sound or more of a feeling like surging or very slight hesitations. A wearing clutch especially a rubber center can feel a bit like out of balance, especially as it chunks rubber out.
  

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OhioTom
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Re: "Fluttering" Under Load
Reply #2 - Aug 14th, 2019 at 6:32pm
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What does "flutter" mean?
Please give greater detail on exactly what the car is doing?
  

Tom Simpson&&VW/Porsche freak.
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Dave W
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Re: "Fluttering" Under Load
Reply #3 - Aug 14th, 2019 at 10:31pm
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That sounds like a slipping clutch.  The 5th gear uphill is the old test for it.
  

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OK-944
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Re: "Fluttering" Under Load
Reply #4 - Aug 15th, 2019 at 6:23pm
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Re: "fluttering"...a bit like a hummingbird, but more muffled, and not quite as quick.

As for the 5th gear "clutch test," this seems counterintuitive.  I'd think a slipping clutch would announce itself while attempting to accelerate briskly from a lower gear.

While the clutch was replaced awhile back, the engine has never been opened and does slowly seep a bit of oil, including from the rear main seal.  I'll be dropping the engine later this fall, with plans to open it up to see what it might need - and my guess is that all will become clear at that point.
  
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T_Ryan.
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Re: "Fluttering" Under Load
Reply #5 - Aug 16th, 2019 at 12:49pm
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Anything loose on the bottom of the car? Under trays, wheel well liners, ect
  
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Re: "Fluttering" Under Load
Reply #6 - Aug 16th, 2019 at 4:26pm
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T_Ryan. wrote on Aug 16th, 2019 at 12:49pm:
Anything loose on the bottom of the car? Under trays, wheel well liners, ect


Yes, the large sheet metal heat shield above the muffler in the rear can vibrate if screws are loose or missing.
  

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OhioTom
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Re: "Fluttering" Under Load
Reply #7 - Aug 16th, 2019 at 4:49pm
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A low frequency hum that is muffled sounds like a drive line vibration of some kind.
Especially since it happens under load.
May have a CV joint in failure mode.
May have an exhaust hanger broken or similar.
May have a balance shaft out of time.
  

Tom Simpson&&VW/Porsche freak.
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anchor
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Re: "Fluttering" Under Load
Reply #8 - Aug 17th, 2019 at 1:41pm
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Roll EyesRod Bearings? Maybe a long shot. There is one TRACK PCA NER PALMER video at a meet that sound like your description but of course flat or gradual height vertical road surface from APR of 2017. It is on U Tube should be easy to find with 944 and rod bearing contrast to other suggestions this far.


You already have a rear seal leak so it does stand to reason the journals are seeking sound velocity at pitch. If you know the frequency or can measure it and it reside between others that are out of range you have your answer because it is a picket fence gap in frequency noise.
Pitch and frequency are easily established when base is known. A great lesson is available but not in particular for this stated problem to be relative so the video if it sounds like and needs a reverberation fond it on U Tube as above.Also known as reverb flutter echo of metal on metal but it is sound my RPM needle was fluttering before the rod bearings were changed out.
« Last Edit: Aug 18th, 2019 at 1:53pm by anchor »  

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