For about the last 25,000 miles our car has had a shimmy when you took of from a dead stop until you got up to say 35 to 40 mph. Then when you would gently apply the brakes it would also shimmy, but if you hit the breaks hard you could not get it to shimmy, so it was not the brake rotors, which Cindy took to the shop three times to have them double and triple check as that is what she thought it was. We just got the transmission rebuilt and low and behold there is no shimmy when accelerating or applying the brakes gently or not. They did not work on anything else in the front suspension. Could the bearings in the transaxle have gone bad and caused the shimmy? Maybe the shimmy that the 2000+ bonniville'* get originates in the transmission not the front suspension. It now drives just like it did when it was a brand new car. Now if we can just get another 163,000 miles on this transmission.
The shop told us to bring the car back in two weeks because they like to do a check at two weeks about 200 to 300 miles. Cindy laughed and said then I'll have to bring in back in about 5 days. She puts 350 to 400 miles a week on the car, and now with the tranny being fixed probably a lot more. The shop guy just looked at her like she was nuts and said well then bring it back between 500 and 600 miles.

ROD

have you had the tires rotated and balanced?

No, the car had the shimmy when i drove it to the tranny shop and no shimmy since we got it back from the shop. The tires get rotated and balanced every 10,000 miles(free at Costco). Rotating the tires did nothing for the shimmy in the past.

ROD

I don't think it was the Torque Converter because it was not rpm related, it had the shimmy/shake with light brake perssure also . This is the same shimmy/ shake that i have seen in other 2000+ Bonneville'*. When we take it back to the transmission shop we will ask them about the shake that'* not there anymore(don't want it back either) it(shimmy/shake) had to originate in the transmission. I've seen guys put a lot of money into their car to try to get rid of the vibration, some people have sold their car because they could not get rid of it.

ROD

Any more thoughts on this? I've made some other posts and am pretty convinced that my tranny is causing my remaining vibration. The vibration is in the pedal and seats, and gets worse when accelerating from like 40 mph+

The other day I was climbing a hill, and was getting worse than average vibration, put it in neutral, and the vibration all went away.... but then when I put it back into drive, the car shifted really horribly in each gear, like a hard shift. Stopped to go to a store and came back 30 min. later and that hard shift was totally gone. Reading some other posts, this phenomenon seems to be from the computer system detecting some sort of slippage (my fumbling between neutral and drive) and making a protective hard shift that can be reset turning the car off for awhile.

But besides changing the transmission fluid and filter, I'm not sure what exactly can be done to fix transmission vibration. All the front end suspension work on my car is done. Anyone have luck with transmission gimmicks like this guy did with his new tranny? (I'm looking for inexpensive ideas-not a new tranny)

Have you checked ALL your mounts?

I think part of the shimmy is from the tc pulsing to over correct for worn clutches.
I've felt it too a couple of times

We have almost 5,000 miles on the new tranny and the vibration/shimmy has not returned(yet). You need to check your inner and outer tie rod ends, if you have any slop in them they need to be replaced.

ROD

x2

Did they install any new mounts? Maybe the mounts were loose?

(Not discounting other possibilities like imbalanced TC, bad PCS solenoid, etc...just that mounts is a possibility)

Speaking of TC, did they replace it? Is it the same stall as what you had?