Experienced Something similiar when i replaced all my mounts. Initially it felt like i was putting out alot more horsepower as aggressive as the thing felt. Turns out thats was just me getting used to what a properly mounted. But it sounds like yours is a little bit more extreme.

The engine runs smooth it is just that you can feel the engine running when you are driving slow or sitting at a stop sign.

is there a difference between the motot mounts you would get from Oriely Auto Parts and the fgenuine Gm parts?

Not sure if there is any difference, but i remember you did say in an earlier post that one of your mounts was collapsed. Meaning you've been driving around with an improperly mounted engine. Now all 4 contact points are solid and properly mounted your gonna feel your engine. How long has it been since you had ur mounts done?

I do realize that I should have some vibration based on new mounts but if you put a cup of coffee on the dash when you are at a stop sign I believe it would vibrate off.

I took the car in yesterday to have the alignment checked at the pontiac dealer and they commented that they have never seen a bonneville that had that kind of enginee vibration.

Last night we loosed up all the motor mounts and while running the car used a crow bar and lifted the engine up just trying to see some change and the ony time the vibration changed was when we lifted the rear transmission mount so I ordered a new rear mount fron GM and hope this is the problem.

Tonight I am going to remove the rear mount and give that a try.

Is there anyone that would know if the Gm rear transmission mount is oil filled or is of a softer ruber than the one from Oriely because the one from Oriely is very rigid and the orginal one was of a softer rubber so any help would be appreciated.

I will post my findings tonight after I remove the rear mount but I have to wait untill tommorrow until the GM part gets here.

Joe

I forgot to mention that these mounts have about 200 miles on them.

Joe

Not a bad idea, but changing new mounts like that can get expensive. If people here change out their rear trans mounts, I don't believe they mention it. I've got my fingers crossed, but I'm ready for more participation if this next step doesn't help.

Well I started out the night with jacking the car up and puttin it on jack stands then put a 2 x 12 on top of the floor jack.

I proceeded to remove the rear trnamission mount and started the car and it removed about 50 percent of the vibration so I removed the front mount also with balancing the engine on the floor jack but this didn't change anything so I pulled my wifes 06 grand prix in the garage and started both and put one hand on engine and the other on the fender and alternated cars and noticed that the grand prix hardly had any vibration tranfered to the fender but the bonneville had quite a bit.

My next step was to look at all of the accessory pulleys to make sure none of those were bent or wabbling and on both cars they all looked good so I removed the belts from both cars and started them again and to my amazement the bonneville was just as smooth as the grand prix so I knew I was on the right track.

Next i went from car to car spinning each pulley on each car keeping in mind how it felt and how it spun and I got down to the last pulley and it was the idler pully and the pulley on the Bonneville was very sticky and would not continue spinning like the one on the grand prix so i swapped the pulley onto the bonneville and put the belt back on and fired it up and it was very smooth so I was so happy I thought I deserve a beer so I did.

The I went to napa and purchsed a new wheel for the bonneville and installed it and it is pretty smooth.

My next step was to look over the rear transmission mount that I bought at O'riely and notied that there was only about 1/4" of rubber between the metal parts and remember that the one that I removed last week was a alot softer rubber and there was about 1 1/2" of rubber between the metal parts so I ordered a new gm mount and will install it tommorrow night and hopefully this problem is solved.

I started it again

I noticed a similar issue with my 04 LeSabre on doing the mounts.
I got mine from Rock Auto. My front mount was totally trashed, and I installed the new one. All of a sudden now I have engine vibrations that can get pretty bad. It has softened up a little with some use, so I tend not to notice as much any more.

But,
I also got a rear trans mount at the same time, same manufacturer. And it is made in Taiwan. No kidding. It looks pretty solid, actually, but its probably too stiff a durometer of rubber, hence why I was having problems with the front mount and vibrations. I didn't install the rear one, but it looks like a lot less material to absorb vibration that a factory GM part. So you are on to something with that. I'll bet yours are probably china or taiwan made as well. It may bolt up right, and do what it is supposed to do, but the softer cushy rubber mounts that are factory originals probably provide more cushion than the cheap and inflexible rubber aftermarket ones.

Well I replaced all the mounts that I had previously installed mounts from Oriely and all of the engine vibrations are gone.

In matching up each mount the front one was not oil filled like the gm part, The rear one the one from Oriely was about a 1/2" taller and the gm was made out of a softer rubber because you could not even move the Oreily part back and forth, The right front one was allot softer rubber also.

The GM parts were about $60 more total but I was able to bring the ones I purchased from O'reily back.

I do have to say I buy 95 percent of my parts from O'reily Autp Parts and have never had a problem and will continue to buy there but just not the motor mounts.

Problem solved.

I can not believe the difference in this car it just drives so smooth with no vibrations from the engine or anything else.

I honestly think O'riely Auto Parts should be paying me for my time to be an experiment because all the B.* I had to go through hear and you can't tell me there was knowone else complaining about these pieces of junk.

What really got me going was when I returned all three motor mounts with all of the slips and the first words out of their mouths was we can not reurn these because I didn't have the original box and I had $166.00 invested in this crap.

I think my eyes must have about poped out of my head at that point because he looked at me and then said maybe we can find some boxes and went to the back room to retreive some boxes and I helped them pack them up so they car return these to tawain.

I think he might of realized he wasn't going to win this one because there was no way I was going to walk out of there without a refund.