I have a noticeable vibration above 3500 rpm (really comes on strong about 4k+). I am sure it is not anything behind the transmission as the vibration is present while running the engine at these rpms in the driveway. The vibration seems to be present both with the clutch in and with the clutch out (in neutral of course). Also, I removed the serpentine belt and ran the engine at 4k for a short amount of time. Vibration still present.

At this point, I am thinking it might be the harmonic balancer. From visual inspection (without removing it from the crank hub), it looks to be in acceptable condition. The car only has a little over 40k miles.

Can these balancers be bad without any visual signs that they have deteriorated? The rubber piece between the inner and outer sections looks to be in good condition. Should I go ahead and pull the balancer off of the hub to give it a closer look?

Aside from the balancer, I'm not sure what else it could be. I guess it could be the flywheel, but I would imagine I'd have more noticeable symptoms with a bad flywheel. I do notice that occasionally when I have the clutch out in neutral, there is a lot of clacking and rattling coming from the ZF. I know some is normal, but occasionally it does sound worse than normal.

The other thing I've considered is a misfire condition at higher rpms. The plugs and wires are A/C Rapidfires and Taylor, and they are all new, so I think this would be the least likely scenario.

This is really puzzling to me. Any help/experience you guys have to offer would be greatly appreciated :cheers:

 

I know this sound silly but I had the same thing happen once......I tracked down all kinds of ideas.....It turned out the brackets that held the alt. on where loose, after tighting all of the bolts to the alternator it went away.....I took it off and reinstalled at a later date and forgot to torque one of the bracket bolts and it felt like the whole car was out of balance between 3500 and 5k, readjusted and it went away.....It may be something simple...hope this helps...

KDD

 

Wouldn't running the engine with the serp belt OFF eliminate the alternator as a possible culprit? If not, I'll be checking the alternator bolts first thing tonight.

 

I imagine it would but in my case it was only moderate while sitting still and very bad while under load...I don't know why.......It would not in my understanding (which is limited) be a good idea to run the car without your assc...you would not be getting the right spark your computer would not be getting the best energy, and you have the potential to overheat due to not turnig the water pump.....Have you had any work done to the car recently??? If so what was it..check what may have been touched while completeing the work etc......

KDD

 

Well, the car is in no danger of overheating because on the LT1 the water pump is driven by the camshaft, not the accessory belt. Also, I would think spark and computer would be ok without the alternator at least for a little while if the battery is fully charged (which it should be).

No modification done to the engine that I know of. It has new plugs and wires, and a custom muffler shop exhaust system (stock manifolds with no cats, though).


[Modified by HammerDown, 11:30 AM 11/21/2003]

 

Mis quoted the water pump my bad (embarrassing)............There is a metal post that connects to the manifold that goes to the side of the alternator this and the stamped bracket covering the valve cover should be pretty easy to check with out having to remove a bunch of stuff......If it vibrates while sitting still then yes I would belleive removing the belt would eliminate that as a problem.....Call Trevor at Exotic Muscle he had told me years ago when I told him of my problem of a alt. that had a seized pulley or something and caused the same problem.........It seems if you removed the belt it would at least eliminate that concern.......

I am very curious to know the issue.....did it start after the exhaust had been installed???? Maybe wire not on all the way????? plug with closed gap????


[Modified by buell_freak, 1:09 PM 11/21/2003]

 

Remove the three bolts holding the balancer and remove it from the engine and try it again. See if the vibration is gone, if its still there it could be something with your clutch. Perhaps a balance weight has fell off. I don't think a dual mass flywheel could do that but then again I could be wrong. At least if you remove the balancer and try it, that would eliminate that one peice.

 

Won't it vibrate like a mother with the harmonic balancer off? It looks like there is only one slug in one of the holes around the outer perimeter of the balancer. There is a little painted dot beside the hole with the weight. I can't tell if there are any other weights until I actually get the thing off of the crank.

As far as wires or exhaust, I am really trying to remember when this whole thing started. I wanted to say it started after the exhaust work, but I can't be sure. I spent a good 30 minutes under the car last weekend to check for clearance around the exhaust system, and there was plenty. No contact whatsoever. As far as wires and plugs go, I did the plugs before the exhaust, and the wires afterwards. Again, precisely remember when this started happening, or when I actually noticed it happening.

I think I am resolved to take the balancer off next, but other than visually inspecting it for obvious deterioration, I don't know what to do after that.

 

ttt

 

No, the balancer is neutrally balanced meaning its at zero. You can run it without the balancer for a few minutes to make the check. GM uses the crossdrilled holes in the balancer to add weight to zero it. The little arrow means nothing really, the 3 hole bolt pattern is not symetric, it can only bold on one way only. But it does mate to a matching arron on the hub.

Even if you have a missfire, reving the engine up would smooth it out. If its a serious engine mis-balance the vibration would be felt regardless. Double check your firing order and make sure that there isn't any crossed plug wires. If your plug wires are stock, they are numbered.


[Modified by tjwong, 11:29 AM 11/22/2003]

 

So in my service manual it says that if you replace the balancer, you should add the same amount of weight in the same hole location in the new balancer as was in the old balancer. To me this implies that the balancers are neutrally balanced, then balanced with the addition of weights to compensate for the imbalance internal to that particular engine.

I doubt I have crossed plug wires. I have been driving it now for over three months since I changed them, and generally you can tell right away when the plug wires are crossed. If you're saying that a misfire condition would smooth out when the engine is revved, then this kinda points to a balancer or flywheel problem.

Can a sticking lifter cause a similar vibration at higher rpms?

To characterize the vibration I'm talking about, it's not a "hard" vibration, more like sitting in one of those heated vibrating chairs at Brookstone.


[Modified by HammerDown, 1:46 PM 11/22/2003]


[Modified by HammerDown, 1:47 PM 11/22/2003]

 

I doubt a sticking lifter would do that, it may cause a mis-fire type of vibration and of course you would hear the lifter as well. You mentioned that you hear a lot of noise coming from the ZF. Is the flywheel and clutch stock or if it had been replaced was it replaced with OEM parts? Mainly I am talking about the dual mass flywheel. Your problem could be in that DM flywheel. One of its main purposes is to dampen any noise from the ZF. A car that has been replaced with a single mass flywheel when idling with the clutch out makes a clattering kind of noise. If you are hearing this and if your car has the stock DM flywheel it could be that the flywheel is the cause of this vibration.

If your engine does have a mis-fire a noise could come from the DM flywheel. As it does have about 30mm of movement to dampen the gear clatter from a ZF transmission. If the flywheel is worn to a point where the range of movement is > 35mm it could make a lot of noise regardless if there is a misfire or not. As you have said you have been driving the car for over 3 months and if you had a engine miss your fuel milage would be bad and performance would also suffer severly.

 

As far as I know, the car has the stock DM flywheel. I have a record of all dealer work done under warranty, and flywheel replacement is not on there. I'd imagine that if it were a single mass flywheel, it would make racket all the time.

I had considered the flywheel being the source of the problem; however, I wouldn't think the flywheel would be bad after only 41k miles. If so, that's got to be some kind of record for shortest life of an OEM flywheel.

I sure hope it's not the flywheel. $$$$$