Vibration at 4kRPM
Thread Starter
Instructor
Joined: May 2010
Posts: 197
Likes: 15
Vibration at 4kRPM
I have a1996 CE LT4 with 33k on it. I bought the car about a month ago and it has always had a bit of a vibration that is coming from the either the engine or drive train.
The car is perfectly fine, pulls strong and drives fine, until you get past 4k RPM. Then there is a bit of a vibration and it also seems like it climbs slower from 4-6k RPM.
I just had the spark plugs replaced and spark plug wires. It seems like the car is not as fast as it should be, and that the RPM should climb quicker.
Any thoughts?
The car is perfectly fine, pulls strong and drives fine, until you get past 4k RPM. Then there is a bit of a vibration and it also seems like it climbs slower from 4-6k RPM.
I just had the spark plugs replaced and spark plug wires. It seems like the car is not as fast as it should be, and that the RPM should climb quicker.
Any thoughts?
Burning Brakes
Joined: Mar 2010
Posts: 1,094
Likes: 68
From: Providence RI
Has the clutch been replaced? Sounds like a vibration from the replacement of the Dual Mass flywheel with a single mass. Search dual mass flywheel and you will be reading for a while.
33,000 miles with a clutch replacement does not make sense, but you never know.
Mike
33,000 miles with a clutch replacement does not make sense, but you never know.
Mike
Race Director
Joined: Feb 1999
Posts: 12,772
Likes: 17
From: Indianapolis IN
I would say to check the rear half shafts, rear U joints and Pumpkin Diff bearings.
Mine does the same thing starting at 85MPH and up, and it all started the day I did a hard drag launch and twisted my POS SCAT crank shaft, and I fear that I twisted something in the rear too.
When I get back from the Hot Rod Power Tour I will take it all down to Patterson Drive Shaft and have them check the balance on the half shafts and look at the Diff-bearings,
Mine does the same thing starting at 85MPH and up, and it all started the day I did a hard drag launch and twisted my POS SCAT crank shaft, and I fear that I twisted something in the rear too.
When I get back from the Hot Rod Power Tour I will take it all down to Patterson Drive Shaft and have them check the balance on the half shafts and look at the Diff-bearings,
Racer
Joined: Jan 2008
Posts: 281
Likes: 3
From: Palm Coast FL
Please, please, if you get to the root of this post your fix. I've been trying to resolve mine for about one year now, although I haven't been too proactive since it is smooth at lower rpms, which is where I spend most of the time 
Le Mans Master
Joined: Dec 2002
Posts: 5,270
Likes: 3
From: Seattle Area WA
Mine was about the same area and had the worst vibes around 4-5k. Seemed to diminish above that point. It was not horrible, but I was not comfortable with it. It turned out to be an out of balance flywheel. A weekend and 30 bucks for a balance job and it is smooth as silk.
You need to isolate it though.
Does it do it only when moving?
Is it RPM or MPH dependent?
Does it do it with the clutch in AND out?
You need to isolate it though.
Does it do it only when moving?
Is it RPM or MPH dependent?
Does it do it with the clutch in AND out?
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Thread Starter
Instructor
Joined: May 2010
Posts: 197
Likes: 15
If I rev it in neutral with the clutch out, it still does it 4-5RPM and up. Also, when accelerating at WOT the RPMs climb slow from 4-6k.
There is also some vibration when blipping the throttle at idle.
Any thoughts?
Le Mans Master
Joined: Dec 2002
Posts: 5,270
Likes: 3
From: Seattle Area WA
Fill in more info:
What makes you say it is exhaust related?
So I did some isolation testing on my way home tonight. It seems like it is actually something exhaust related, maybe the cats?
If I rev it in neutral with the clutch out, it still does it 4-5RPM and up.
Still? Does this mean it also does it with the clutch in? ---- If it does, this isolates the gearbox out of the equation.
Also, when accelerating at WOT the RPMs climb slow from 4-6k.
As compared to what? You said the vibration was always there during your ownership?
There is also some vibration when blipping the throttle at idle.
At the same RPM or different?
Did it show up at the same RPM in different gears?
Any thoughts?
If I rev it in neutral with the clutch out, it still does it 4-5RPM and up.
Still? Does this mean it also does it with the clutch in? ---- If it does, this isolates the gearbox out of the equation.
Also, when accelerating at WOT the RPMs climb slow from 4-6k.
As compared to what? You said the vibration was always there during your ownership?
There is also some vibration when blipping the throttle at idle.
At the same RPM or different?
Did it show up at the same RPM in different gears?
Any thoughts?
Last edited by USAsOnlyWay; May 9, 2012 at 09:27 PM.
Thread Starter
Instructor
Joined: May 2010
Posts: 197
Likes: 15
Le Mans Master
Joined: Dec 2002
Posts: 5,270
Likes: 3
From: Seattle Area WA
To check this and any other accessory related symptoms, just pop off the belt and see if it still happens. If it does try to get a good look at your harmonic balancer.
If it does, it could be exhaust or clutch/flywheel or a separating harmonic balance, bent crank etc.
If you really think it is the cats, drop em and rev it up without the cats connected and see if it goes away.
Pro
Joined: Aug 2009
Posts: 725
Likes: 4
From: Plano, TX
