Vibration during acceleration from dead stop

2000 Buick Century, 3.1 L
I just had my transmission rebuilt and after a few weeks of it working just fine, a vibration started when I accelerate relatively hard from a dead stop. It feels like the engine is coming out of the engine compartment (it almost feels like the wheels are spinning and hopping). The shop pulled the transmission but can't find anything. The motor mounts are fine and there is no indication of anything loose.

The transmission was initially rebuilt because it was shifting real hard into each gear.

We're starting to wonder if it is in the engine.

Any ideas?

Thanks,
Ray

I seriously doubt it is the engine. Other than the hard shifting did you have this problem before the transmission rebuild? It sounds like the tranny shop screwed up the rebuild. You are getting what is referred to as "launch shudder" which is transmission related. In most cases it is caused by a bad pressure control solenoid and its inability to properly control line pressure. Was any valve body or solenoid work done when it was rebuilt?

Thank you for the quick reply. I did not have this problem before the rebuild. It was hard shifting (more like slam shifting) that initiated the rebuild. After the rebuild it worked fine for about 3 weeks. It is now back in the shop (under warrenty) and they have pulled it apart again. I believe he said the pressure control valve was replaced. Last night they had gauges hooked up so they could monitor the pressure but I haven't received an update yet as to whether they found anything.

What controls the pressure control solenoid? If the valve and solenoid ar OK could it be the signal to it? or a feedback loop problem?

I'll let you know what found out

Ray

Thank you for the quick reply. I did not have this problem before the rebuild. It was hard shifting (more like slam shifting) that initiated the rebuild. After the rebuild it worked fine for about 3 weeks. It is now back in the shop (under warrenty) and they have pulled it apart again. I believe he said the pressure control valve was replaced. Last night they had gauges hooked up so they could monitor the pressure but I haven't received an update yet as to whether they found anything.

What controls the pressure control solenoid? If the valve and solenoid ar OK could it be the signal to it? or a feedback loop problem?

I'll let you know what found out

Ray


The electronic device that controls the PCS and line pressure is the Powertrain Control Module (PCM) but I have never seen a PCM cause this problem but you never know. Also, I would not rule out the torque convertor.

Good luck and let us know how it turns out.

Well, I have it back from the shop and it seems to work well now. They said they pulled it apart and replaced a few components (he mentioned clutches) but were unable to trace it to one thing. He said they hooked up some gauges with long hoses so he could watch the computer and pressures in the vehicle while driving it and everything seems to be shifting fine now so whatever it was, it's gone.

He also said there are some suspension issues that could be contributing to misaligment and adding to the problem particularly when the weight off the vehicle is transfered to the suspension from a stop. I know my right front strut is making noise, sounds like play in the strut tower cap.

Take care and thanks for the replies,
Ray

Well, I have it back from the shop and it seems to work well now. They said they pulled it apart and replaced a few components (he mentioned clutches) but were unable to trace it to one thing. He said they hooked up some gauges with long hoses so he could watch the computer and pressures in the vehicle while driving it and everything seems to be shifting fine now so whatever it was, it's gone.

He also said there are some suspension issues that could be contributing to misaligment and adding to the problem particularly when the weight off the vehicle is transfered to the suspension from a stop. I know my right front strut is making noise, sounds like play in the strut tower cap.

Take care and thanks for the replies,
Ray
If this condition returns, suspect the inner tri -pot joint on one of the front axles, typical symptoms of one being frozen in it's housing.

If this condition returns, suspect the inner tri -pot joint on one of the front axles, typical symptoms of one being frozen in it's housing.

I disagree Shep. It is a classic symptom of a screwed up 4T65E tranny. I had the problem in my GTP over three years ago at the track. It is a violent shudder where the whole front end of the car bounces up and down and there is a hellacious sound when it happens. It occurs from a standing stop and pedal to the metal. A new PCS and Trans-go Valve Body Kit resolved the issue for me. I have never had a CV joint or axle half shaft cause that type of problem.

I disagree Shep. It is a classic symptom of a screwed up 4T65E tranny. I had the problem in my GTP over three years ago at the track. It is a violent shudder where the whole front end of the car bounces up and down and there is a hellacious sound when it happens. It occurs from a standing stop and pedal to the metal. A new PCS and Trans-go Valve Body Kit resolved the issue for me. I have never had a CV joint or axle half shaft cause that type of problem.
Bob, this is fun, I have seen several cars with this problem in the shop. When the joint locks up, as the attitude of the front of the car changes, the effective length of the axle must change, when it cannot it rocks the engine back and forth on it's mounts causing the described condition. So I guess there are 2 possibilities for similar symptoms, in this case the odds seem to favor the trans as it did not act this way before, unless they damaged the axle during the process. I re-read the description of the symptoms and yes it would seem the shudder on accel would more likely be caused by heavy clutch chatter.

Well ,the "shudder" problem came back. The shop put in another transmission and it is still doing it.

Frankly, we're all confused.
We did notice that the motor mounts ha
ve some play in them.

I've replaced the shocks, plugs, wires and ignition coils as well as had a wheel alignment.

Could the mounts be the problem?

Any other ideas?

2000 buick century 3.1 L

Had a similar problem in a 2000 bonneville. Had a bad inner axle joint. Mine ended up to be the driver's side, but it was a guess. I bought both and replaced that one first and problem solved. It shuddered hard from a dead stop acceleration and also if you were slightly in the throttle and hit train tracks, etc.

Had a similar problem in a 2000 bonneville. Had a bad inner axle joint. Mine ended up to be the driver's side, but it was a guess. I bought both and replaced that one first and problem solved. It shuddered hard from a dead stop acceleration and also if you were slightly in the throttle and hit train tracks, etc.


Thanks for the reply. How do you check if the axle joints are bad?

I'd tell you if I knew, that's why I had to guess. I tried to figure it out by turning during acceleration and picking which side seemed worse. My guess was driver, but I had a transmission guy drive it and he said passenger, so your guess will hopefully be as good as mine.

I had a simlar problem except the car wobbled to some degree. The Buick Dealer wanted to replace my transmission for 2-3k $. I pulled both axles and replaced. The car vibration went away.

I had a simlar problem except the car wobbled to some degree. The Buick Dealer wanted to replace my transmission for 2-3k $. I pulled both axles and replaced. The car vibration went away.

I have a 2000 century with a vibration while at hwy speeds (60mph and up). Feels a lot like a tire out of balance only much worse. Found a noisey outer passenger side CV joint as a probable cause. How big a job is replacing this half shaft? Do you need the special tools indicated in the chiltons manual or are there substitutes? I have a hub puller, wondering more about the special GM slide hammer to remove the shaft from the transaxle. Can the job be done with the car on jack stands or does it need to be on a lift? Any advice would be appreciated.