Strange pulsing vibration at 3k rpm

[BobsBonneville]

Hi all, I'm new here, and this looks like the best forum for Bonnevilles. I have a 2003 SSEI, 125k miles. Since I bought it a few months ago, any time the car runs up into the 3-4k rpm range, there is a vibration. The only way I can describe it is like a pulsing vibration or shutter. It only happens between 3 and 4 thousand rpm, not below, or above. So I tend to drive the car nicley and keep it under that range to avoid it. I can't tell if its coming from the engine or the tranny. Its very prominant in first gear, and then in second and third its not so bad and the pulsing also slower in second or third. Any ideas? Anyone Bonneville owners experience anything like this?

[deano55]

Sounds like mine, maybe motor mount

[spoiledred94]

I hope I'm not hijacking your thread BobsBonneville, just a quick related question. Deano55's diagnosis seems like the same thing on my car. Except my car vibrates at 30+mph and is independent from the motor RPM. I replaced the broken fr mount with the hockey pucks. Could it be one of the other mounts?

[BobsBonneville]

Ya, I also replaced my front engine mount that was in bad shape, and the problem still persisted. Could it be the other engine mount that needs replacing? Where is it located?

[spoiledred94]

there's at least 2 more engine/frame/trans mounts. I think there are 1 behind each wheel.

[BobsBonneville]

Ok so I was under the car a few hours ago due to a oil pressure switch issue, and I looked at the rear mount, and it was in good shape. But looking around I noticed that a bolt was loose where the front axle goes into the tranny. On that half circle part where the axle comes out, the bolt on top was loose, it also holds down a bracket that goes to something. So I tightened it. And now the vibration at 3k rpm is gone! BUT, now there is a vibration at about 1,500 rpm. *dang* it! So now when I'm at crusin speed I can feel a vibration. I can feel it in the gas pedal. So I'll get back up under there and make sure all the bolts are tight on each side, and then otherwise I don't know.

[spoiledred94]

very interesting. Where did you find the rear mount and what shape was it? I'm a little unclear where your bolt and bracket are. Which side of the car? Are you sure your alignment is good?

[BobsBonneville]

From reading old threads here, I found out that there are rubber mounts behind each front wheel and directly behind the tranny. It seems like its kinda a sub-frame up under there with mounts squeezed to the body. Also from reading, these rear mounts usually stay in good shape on these cars and some guys have replaced them anyways to try and get rid of vibrations or shutters... to no avail. I looked at it briefly, it was more or less directly behind the tranny squeezed between the body and a bracket or sub frame of some sort. It was square, and in good shape.

I'm not sure how else to describe where the loose bolt was. Get up under your car and you'll see what I'm talking about. It was the passenger side front axle goes into a half circle shaped chunk of aluminum thats bolted to the tranny. More or less it IS part of the tranny. And it has four or five bolts holding it on, one of them was loose...the one on top which also held down a bracket to something. I see no need to get an alignment, tires wear evenly and it drives straight.

[spoiledred94]

Hey I rebuilt my trans and I know just what assembly you're talking about. That's the differential housing. It houses the gears that set the FDR (final drive ratio). It has that complicated bracket and mount. And I remember now that the oil pressure sender is right there on the engine.

I am not saying get an alignment. Just an idea -Good Luck Bob'sBonneville

Kris

[deano55]

Well there goes my thought out the door, although its past time to change mine

[spoiledred94]

That's good idea. It could easily be a loose bolt. The sub frame to chassis bolts may be likely.

[BobsBonneville]

Just an update, I was under the car today to replace the oil pressure switch and that bolt had worked its way loose again. Hmmmm. Something is causing that bolt to vibrate loose. And the bracket that bolt holds seems to go to the engine block from what I can tell.