Vibration

Hello,
I recently replaced the flexplate in my 97 Riviera SC. I had small vibration at idle (before the flexplate broke), which has gone away with the new flexplate. The problem is that 2500-3000RPM, there is a sort of vibration, or humming I can feel, just enough to be annoying.

The interesting thing is that in neutral, I rev through the entire RPM range and it doesn't do that. It is only when driving and under load, so it is not likely an engine balance issue.

I wonder if it has to do with the engine's dual intensity ignition system.

Any suggestions?

Thanks.


PS. The catalytic converter has been gutted. The ceramic had started to break. Interestingly, no check engine light.

Mikel wrote:

Hello,
 I recently replaced the flexplate in my 97 Riviera SC. I had small vibration at idle (before the flexplate broke), which has gone away with the new flexplate. The problem is that 2500-3000RPM, there is a sort of vibration, or humming I can feel, just enough to be annoying.

The interesting thing is that in neutral, I rev through the entire RPM range and it doesn't do that. It is only when driving and under load, so it is not likely an engine balance issue.

I wonder if it has to do with the engine's dual intensity ignition system.

Any suggestions?

Thanks.


PS. The catalytic converter has been gutted. The ceramic had started to break. Interestingly, no check engine light.

I am thinking you have at least one weak or failed motor or transmission mount.

Albertj

Will check. Thank you!

You can also try rotating the converter relative to the flex plate. Take out the converter to flex plate bolts, and rotate the converter and bolt it back up. Sometimes there are minor imbalance issues that are magnified when parts are aligned in a certain way. It is sort of like a rim and tire.

LARRY70GS wrote:

You can also try rotating the converter relative to the flex plate.  Take out the converter to flex plate bolts, and rotate the converter and bolt it back up.  Sometimes there are minor imbalance issues that are magnified when parts are aligned in a certain way.  It is sort of like a rim and tire.

I thought of that, but the engine does not vibrate when not under a load, which in my opinion rules out balance issues. It only happens under load.
Thanks.

Mikel wrote:

LARRY70GS wrote:

You can also try rotating the converter relative to the flex plate.  Take out the converter to flex plate bolts, and rotate the converter and bolt it back up.  Sometimes there are minor imbalance issues that are magnified when parts are aligned in a certain way.  It is sort of like a rim and tire.

I thought of that, but the engine does not vibrate when not under a load, which in my opinion rules out balance issues. It only happens under load.
Thanks.

I would still try it, the last thing you did is replace the flex plate.

LARRY70GS wrote:

Mikel wrote:

LARRY70GS wrote:

You can also try rotating the converter relative to the flex plate.  Take out the converter to flex plate bolts, and rotate the converter and bolt it back up.  Sometimes there are minor imbalance issues that are magnified when parts are aligned in a certain way.  It is sort of like a rim and tire.

I thought of that, but the engine does not vibrate when not under a load, which in my opinion rules out balance issues. It only happens under load.
Thanks.

I would still try it, the last thing you did is replace the flex plate.

True.  This is what my old flexplate looked like... For some reason, it vibrated a bit in that condition. Can't imagine why

Wow! Looks like one of the holes is egged out too. Must have made quite a noise too.

LARRY70GS wrote:

 Must have made quite a noise too.

You cannot comprehend the amount of noise that made

But it started, ran and drove!

Mikel wrote:

LARRY70GS wrote:

 Must have made quite a noise too.

You cannot comprehend the amount of noise that made

But it started, ran and drove!

Actually I can. My 1972 Skylark 350 did that to me. A big central portion of the flexplate broke off and got wedged between the teeth and the inspection cover. Sounded like a buzz saw X2. I thought I blew the engine as I had floored it to get on the highway.

I am looking for ideas. '97 SC, developed a serious vibration. Checked the harmonic balancer and it appeared bad so I replaced it with a Dorman. Better but still some vibration. Replaced the trans mount at the front left of the car. Better but still vibrating. Replaced the right trans mount (the one nearest the rear of the car) but no improvement. The vibration occurs in park but is magnified under load, worst at 1200-1700 RPM. At it's worst it almost growls. At times though it almost disappears. It's mostly present but does become minimal for no apparent reason but briefly.

Any chance I have a bad (although new) harmonic balancer? An acquaintance tells me he has a friend that had to replace the Dorman - it was out of balance out of the box. Thanks!

I had a dorman/autozone brand balancer and it shattered at the hub 6 months after installing it. Sheared off the keyway in the crank and was not a fun day. There is a thread on here about it somewhere.
I would return it and get only the acdelo one.

Mr.Riviera wrote:

I had a dorman/autozone brand balancer and it shattered at the hub 6 months after installing it. Sheared off the keyway in the crank and was not a fun day. There is a thread on here about it somewhere.
I would return it and get only the acdelo one.

I keep coming back to the harmonic balancer being unbalanced out of the box. This all started within the last 1,000 miles or so - maybe less. Started barely noticeable and got progressively worse. So I suppose a different one would be a good idea, especially since the symptoms are so typical of the balancer. Thanks!

Problem identified but not solved.

Everyone knows the stud and spacer at the bottom of the engine mount bracket needs to be removed in order to change belts. My stud/nut/spacer is gone. There is no way it can fall out so someone removed it at some point. Now the top bolt in the bracket has snapped under the load so the motor on the passenger side is hanging on what's left of the broken bolt.

The missing nut, GM #11515744 is still available. The spacer, #25622369 and the stud, #24502416 are no longer made. I have been searching diligently but no luck. Anyone have these lying around?

The nut is an M12x1.75 thread so I know the diameter and thread of the stud. I suppose I could have a machine shop make the spacer and stud if I knew the lengths which I should be able to ascertain from under the car, unless someone knows these off the top of their head.

I'm glad to purchase parts if you have them available.

And thanks to all of you who post solutions here - you are amazing!