FYI, see this TSB:

TSB From A Pontiac Bonneville

Steering - Steering Column Clunk Felt/Heard on Turns
Bulletin No.: 06-02-35-010
Date: May 09, 2006
TECHNICAL Subject:
Clunk Felt/Noise Heard From Steering Column, Steering Gear and/or Front of Vehicle During Maneuver and/or Steering Wheel Rotation (Replace Intermediate Shaft)
Models:
2001-2004 Cadillac Seville - with RPO JL4
2001-2003 Oldsmobile Aurora
2000-2005 Pontiac Bonneville
Attention: This bulletin ONLY applies to the above listed vehicles. All other cars with a similar condition should refer to Corporate Bulletin Number 01-02-32-001G.
Condition:
Some customers may comment on a clunk type noise coming from the front of the vehicle while driving during a turning maneuver. This condition may also be felt through the steering wheel when the vehicle is stationary and the wheel is rotated from steering stop to steering stop. Some vehicles may only exhibit the noise once for every 360°of wheel rotation. On all other vehicles, this clunk noise will be noticed during low speed acceleration or deceleration, typically in light turns of the steering wheel.
Cause:
This condition may be caused by inadequate lubrication of the steering intermediate shaft which results in a slip stick condition possibly resulting in the clunk noise.




Diagnostic Tip
Important: This condition is commonly misdiagnosed as originating in the steering gear and has resulted in the replacement of numerous steering gears without correcting the concern.
Engineering Investigation shows that numerous steering gears have been misdiagnosed and replaced. The investigations shows that if the technician incorrectly diagnoses the steering gear as the cause of the noise and/or clunk during replacement of the steering gear, the technician may stroke and/or cycle the I-shaft, distributing the original grease in the I-shaft. This distribution of the original I-shaft grease temporarily may eliminate the I-shaft clunk so that the technician believes the noise and/or clunk is corrected with the steering gear replacement and returns the vehicle to the customer. After the customer drives the vehicles for several miles and dissipates the original grease, the noise may return.
Attempt to duplicate the customer'* concern and isolate the I-shaft by following the procedure below:
1. Locate a large area (parking lot) where the vehicle can be turned in a tight circle.
2. Turn the steering wheel to the right and/or left all the way to the steering lock, then off the steering lock a 1/4 turn.
3. Drive the vehicle approximately 5 km/h (3 mph) in a circle, preferably over rough pavement or seams on the road surface.
4. If a clunk is felt in the steering wheel, the MOST likely cause is the I-shaft - not the steering gear. Continue with the correction.
Correction
Important: The replacement steering intermediate shaft is physically different in appearance than the original. However, the vehicle'* ride performance will not be affected.
Replace the original concentric style steering shaft with P/N 26068295, a Double "D" design. Refer to Intermediate Steering Shaft Replacement in SI

I thought i would enlighten on what is acutally happening, there are three different things that cause this to happen

The first is the Slip/Stick [or what I like to call Slip/SLAP,]because you pay 5 figures for a car that after 30-40k you develop problems and is a slap in the face]

It is cause by the lack of shaft lubrication and as the body to frame expands and contracts from turning, the shaft will "stick" and cause a clunk when it releases
This is why greasing or oiling would give temporary relief, if problem was related to this
[quite common on drive shaft of trucks as well]

The next is rotational play
On the first series shafts with the splines, play would develop between the splines and cause the intermittant "thunk" in the freeplay of the wheel
Filling the shaft splines with grease would act as a buffer when using a good extreme pressure grease and give some benifit, yet temporary until the grease thins out,and was partially eliminated with the newer douple D design>> [Been a big problem with GM truck sterring shafts as well]

The last is Joint Arthritus
On each end of the shaft is a Ujoint. One of the bigger issues that has plagued most shafts is the tight angle that these are installed. The joint is not greaseable and the excessive force that is put on the joint, causes flat spots in the bearings.. this is the feel that gives you the "cardboard over the grill, feel" as you turn. Not much you can do for this as the joint is not greasable unless you try to feed some lubricant into it.
when you take your shaft out, rotate the joints by hand and if you feel any resistance or jitteryness, replace the shaft. The internal failure doesn't allow the joint to turn with out resistance and passing thru vibration

The 2000 I just bought, i would have gambled big bucks I needed a steering rack [had sitting still side to side play, turning clunking and hitting bump, thunking. shaft was orig and small rotational play but lots of arthritus in the upper joint. Replacement shaft, cured all three, for NOW

Hope this helps

I just bought my Bonneville a couple of weeks ago. I knew when I bought it the intermediate shaft was bad because they have gone bad on damn near every recent GM product I or any family members have bought ('07 Aura, '07 Impala, '05 Tahoe, etc.). I bought a new shaft and will be installing this weekend. I'm assuming it is pretty simple and straight forward but the links to instructions in this thread no longer work. Anybody have any new links?

I found the instructions elsewhere. I just installed the new shaft myself. It took literally 15 minutes to get the old one out and I thought it was going to be a piece of cake. Needless to say, things are never that easy. The new design shaft was quite difficult to get up inside the boot as the upper U-joint is almost the same diameter as the boot opening. Here'* a few tips:

- Take your time putting the new shaft in the boot. It'* a tight squeeze but it does fit.
- Once you have the new shaft in the boot, pull it back down a little toward the steering rack. It will free up a little space for the shaft when you are trying to reattach it to the steering column.
- Use a long screwdriver in the U-joint to help you get the intermediate shaft up into the steering column.
- Twist the underhood boot as you pull down on it to get it to come back down to the steering rack.

All told it took me 1 - 1.25 hours to complete the install. 30 plus minutes of that was just trying to get the intermediate shaft in the correct position and reattached.

I replaced mine with the new "D" design one about 18 months ago, and it is now cluncking again. Looks like I need to remove it again and regrease it... Oh well...

I had my 04 GXP intermediate shaft replaced yesterday at 18,400 miles by a mechanic from my local Pontiac stealership. He only charged me $40 for the labor at his house. The new part # on the shaft is #25810450 . I bought it from GMPartsDirect.com cost is $97.65 plus shipping ($20.51). The mechanic told me that this new shaft would cure the problem and that relubing the older versions was only a temporary fix. From what I have read on this forum , I hope he is right !!