New harmonic balancer installed-now low rpm vibration!

[390Merc]

Just installed a new ATP brand harmonic balancer on my 95 Bonneville SE. As soon as I started it up a couple days ago after the installation there is a very noticeable vibration at idle and lower rpm range.
I even pulled it back off and reinstalled after making a quick check of things and still the same. I think it may be out of round or something. I'm picking up another today and installing it tonight. The store will take the "bad" one back.
Anybody have a similar experience with this?

[MattStrike]

I've never had that with a balancer, so if the new part doesn't fix it check out the motor mounts next.

[390Merc]

Just installed another identical balancer, same brand, same low rpm vibe, though a wee bit different now. If you just barely hit the throttle you can really feel it right before it comes back down to idle.
Hmmmm, it never had this before, I suppose it could be one of the motor mounts on that side but they look fairly solid. Perhaps the effeciency of the harmonic balancer doing its job is letting the rubber in the motor mounts dish out what the old balancer was absorbing before?
I'd almost try a different brand of balancer just to rule out the ATP brand, if that is whats at fault at all. I'm very effecient at changing balancers now. I think I could easily do it in a half hour now. Its just jacking up the car shoring everything up that takes any time at all.

[Jrs3800]

95 was an odd year... and iirc the balancer for the Series I L27 although it looks identical to the L36 is balanced differently.. The balancer for the 95 L27 Tuned port motor is specific to that engine alone...

The series II you have will cross to the 96+ 3800 II engines.. If you have a vibration you didn't have before than I would have to believe the balancer is the issue.. You should be able to use any balancer from an NA 3800 Vin K or Vin 2 with no issues as the service balance is 100% the same.. The 2000 and up Bonneville used a newer style balancer but again same service balance..

[390Merc]

My 95 is a VIN K car so a balancer for a 95 thru 99 should work I would think. I ordered a cheaper one off ebay that is a different brand so I'll see how that pans out later this week and post results.

[Zazou]

I have a brand new GM HB that I bought from a Chevy dealer last May. I though my HB was bad on my 98 I had just bought, but it was the piston bearings. So I replaced the engine. It's yours if you want it $100 plus shipping.

[390Merc]

Since the installation of the 2nd ATP brand balancer, of which I still had the very noticeable vibration at idle and still detectable at low rpm/speed, the car also developed the familiar bucking symptoms associated with bad ignition wires and/or plugs.
I bought a $20 set of wires at advance auto parts thinking my current wires couldn't be bad already, having just replaced them along with the plugs a few months ago. Take off out of town and still the bucking occurs shortly after converter lockup in OD, maybe even worse now.
In the meantime, the UPS guy drops off the $27 harmonic balance (plus $10 shipping) I bought off ebay last weekend from dependableautoparts. Great, so I pull the car in the garage and remove the 2nd ATP brand balancer I bought last weekend. Install this generic balancer that came in a plain cardboard no-name box and now my engine idles and runs perfectly smooth!
This was for a VIN K 95 Bonneville SE according to the listing and its obviously the correct one for my car.
So why couldn't the parts store sell me the correct balancer? Is ATP just a bad brand when choosing one for my application? I will return both "like new" ATP balancers to the store, as they were $85 to $90 each. I'm sure they will work just fine for somebody else's non-1995 3800 car.

[Jrs3800]

Sometimes the listings are a bit funky... And some parts will cross where they really shouldn't...

Glad you got it fixed..