Dreaded vibrations.
Thread Starter
Racer
Joined: Nov 2017
Posts: 269
Likes: 24
From: San Antonio
Dreaded vibrations.
Hello All,
I'm hoping the wealth of knowledge here can help with my issue. I will be delving a bit more into it to try and get more info for you, but I wanted to get the conversation started haha.
So I just picked up a 96 lt4 with a zf6. I do not believe it's stock, but am not certain of all the mods. It has a full exhaust and definitely has a little lope at idle which makes me think a mild cam.
So what I'm experiencing is a high frequency vibration at 3k rpm that sounds gosh awful too. The car accelerates just fine, but once 3k comes, it just makes me want to let off and baby it.
If I accelerate hard through it, it sorta smooths out after about 3700 or 4000. The slower I'm accelerating, the more pronounced it is.
It persists with or without depression of the throttle while at ~3k.
It does do it while sitting in place and reving the engine, albeit it a bit less pronounced.
I watched the balancer as it was idling and nothing seemed wonky or out of round as it was spinning, although admittedly I have never actually seen a separating harmonic balancer.
I have heard there is a way of balancing the flywheel without taking everything apart.
Would you guys mind giving me some guidance on this?
I'm hoping the wealth of knowledge here can help with my issue. I will be delving a bit more into it to try and get more info for you, but I wanted to get the conversation started haha.
So I just picked up a 96 lt4 with a zf6. I do not believe it's stock, but am not certain of all the mods. It has a full exhaust and definitely has a little lope at idle which makes me think a mild cam.
So what I'm experiencing is a high frequency vibration at 3k rpm that sounds gosh awful too. The car accelerates just fine, but once 3k comes, it just makes me want to let off and baby it.
If I accelerate hard through it, it sorta smooths out after about 3700 or 4000. The slower I'm accelerating, the more pronounced it is.
It persists with or without depression of the throttle while at ~3k.
It does do it while sitting in place and reving the engine, albeit it a bit less pronounced.
I watched the balancer as it was idling and nothing seemed wonky or out of round as it was spinning, although admittedly I have never actually seen a separating harmonic balancer.
I have heard there is a way of balancing the flywheel without taking everything apart.
Would you guys mind giving me some guidance on this?
Safety Car
Joined: Mar 2017
Posts: 4,206
Likes: 1,325
From: LeClaire Iowa
If it has a cam then the damper has been removed before. Hopefully they used some antisieze so it will come off easy the second time. It is not hard to remove. Your choice is to buy new or have yours rebuilt by the "Damper Doctor". I would choose the rebuild myself. This is the first thing I would check. Dan
Get your balancer rebuilt and original returned
Get your balancer rebuilt and original returned
Last edited by Whaleman; Apr 13, 2025 at 03:32 PM.
Thread Starter
Racer
Joined: Nov 2017
Posts: 269
Likes: 24
From: San Antonio
If it has a cam then the damper has been removed before. Hopefully they used some antisieze so it will come off easy the second time. It is not hard to remove. Your choice is to buy new or have yours rebuilt by the "Damper Doctor". I would choose the rebuild myself. This is the first thing I would check. Dan
Get your balancer rebuilt and original returned
Get your balancer rebuilt and original returned
I was looking at it while it was spinning and it didn't seem to be out of round. Is there a better way?
Safety Car
Joined: Mar 2017
Posts: 4,206
Likes: 1,325
From: LeClaire Iowa
I really don't know any more than you can learn with a google search for "signs of a bad harmonic balancer". Vibration is a main sign. The reason I said to start there is it is a way easier problem to solve than the alternatives. Dan
Pro
Joined: Jul 2007
Posts: 539
Likes: 117
From: New Braunfels Texas
Has the clutch been replaced? The factory flywheel balance is hard to match and can lead to vibration. Also, urethane transmission and engine mounts can transmit an extra amount of nvh that would otherwise not be noticed.
Thread Starter
Racer
Joined: Nov 2017
Posts: 269
Likes: 24
From: San Antonio
The flywheel looks stock though. Has all the holes to add weights on the perimeter.
