I have a 2000 Buick Century that I was given a couple months ago. Only has 46k miles on it and was owned by my parents for about 8.5 years.

Right after I got it I changed the tranny fluid (had never been done) and the first time I drove it I noticed that at certain throttle settings from a dead stop, it will shudder noticeably. It only does it from a stop and only at that particular application of the throttle (like 1/4 throttle). Gentle starts are normal. I have no idea if it did this before the fluid change but I had never noticed it.

Now, I have no idea why I tried this yesterday but if I start moving with the selector in "1", it will not do it. With the car in "2" or "1" the "TRAC OFF" light is on which I am assuming means traction control is disabled.

So, any ideas on this? I appreciate the help.

The tranny also sometimes shifts hard once the car is warm and has been driven for a while but it otherwise shifts great.

 

Sounds like the Torque Coverter Clutch solonoid in the trans sticking. Try driving it in Drive instead of Overdrive. That should keep the solonoid from engaging.

 

Actually this car has 1, 2, 3, and OD as settings but I did try it in "3" this morning. Same thing. It will only NOT do it when the car is in "2" or "1" and the TRAC OFF light is illuminated.

Any more ideas?

Thanks.

 

First thing I'd do is get the codes read.
I suppose it could be something with the traction control. Does it have a switch to turn it off manually? If so try turning it off and then drive in OD and see if it still shudders.
Just kinda trying to isolate a system here.

 

There isn't any switch to disable the Traction Control so the only way to turn the system off is to put it in low (1 or 2) or apply the emergency brake. Maybe I'll try putting the parking brake on slightly and see if I can replicate shudder. We'll see what happens and report back.

Also, there are no codes showing up on my reader. Would tranny codes need a special reader or should they show up on the OBD-II/CAN reader I have?

 

I had a 98 Lesabre that did that and only a few times before I carried it to the dealer to fix under warrenty.
I don't know what they did to fix it.

 

(LOGIC CHOPPING MODE)

It does it when "3" or above is engaged

No idea if a particular fluid is REQUIRED, and may not now have it

"SHUDDER" is typical of a clutch surface with a worn out material that now is metal-to-metal, and grinding up.

Continuous operation under recommended OD speeds IN OVERDRIVE can lead to premature wear of the transmissions clutches (particularly in the higher ranges)

*This gearbox is displaying signs of a unit that has been ignored, and wore out from uneducated use. An OD tranny that is left in OD constantly can turn into a machine that does exactly what you have described. The clutch packs can be replaced, and that ought to cure it.

 

Did you ever solve trans shudder 1st and 2nd fine with traction off light, have same problem Thanks

 

I never did figure it out. I sold the car to a guy and told him about it even though it never did shudder during the test drive. He said he wasn't worried about it. I got a fair price and never heard from him again. :-)

Good luck.

 

Thanks for your response, I did figure it out I own a small general auto repair business and always utilize all data and internet blogs for further info it is sometimes very helpful, I took transmission pressure readings which indicate low fluid pressure in drive, that transmission utilizes a band and servo in first gear, the reason it doesn't happen when you put it in 1 or 2 it activates a second band and the fluid pressure doubles causing the servos to apply more pressure on the bands hopefully this may help others, there is no easy fix pressure can be lost not only through the pressure control solenoid but also the valve body and various seals ultimately you need a proper transmission rebuild from a qualified rebuilder, Thanks again