Shuddering Grand Prix

A couple of months ago my 2001 Pontiac Grand Prix GT (90,000 miles) began shuttering when accelerating in turns. It is most pronounced on interstate onramps. My mechanic experienced the vibration on right turns only. He inspected the front suspension and motor mounts and was unable to find a problem. He suggested I try taking it to the Pontiac dealer. I held off on trying the dealer as the car was about due for new tires and I wanted to see if replacing them helped. Two weeks ago I purchased 4 new Bridgestone tires and had a 4 wheel alignment. The tie rod ends were replaced at this time also. The shudder is still there. I am also now feeling a slight vibration when driving in a straight line. However, when accelerating in turns it is considerably worse. When not accelerating the vibration goes away completely. If I coast around a turn without applying the throttle there is no vibration at all. Any ideas?

Has anyone checked the CV joints?

Ask around, of friends and acquaintances, of an Alignment Shop they have received good service from. There are some problems, such as in the suspension, where Looking won’t reveal the cause. The components may need to be actuated (moved) to determine the cause.

The invoice says the cv boots were inspected and found to be ok, it does not mention the cv joints.

Sometimes CV joints develop a wear pattern in which a clicking or knocking does not exist but may cause a vibration. The only way of determining this is by removal of the halfshafts and inspection by feel.
Of course that leads to the question of is it wise to reinstall a 90k miles halfshaft back into the car if it is not blatantly bad.

One could assume that if the problem was worsened on a right turn then the left halfshaft is the one that could be at fault. I’m assuming here that tie rods (not the same as T R ends), wheel bearings, and ball joints are fine.

The mechanic did replace the tie rod ends so would it be logical to assume he inspected the tie rods as part of this process? I do not believe either the ball joints or wheel bearings were inspected.

The shuddering has gotten worse so I brought it back in to the shop and they did a more thorough insection. The mechanic believes that it needs a motor mount, a transmission mount and an inner cv joint (the boot is leaking). His estimate to fix all three things is $665. Does this sound like a reasonable price?

Have you checked the ignition system? No mech should miss the mounts on first inspection as you have reproted. I had a spark issue that was shuddering on accel but the car seemed to idle fine. The issue is that cv joints can cause shaking driving forward but usually don’t. Your problem seems accel related so its possible that the fuel and or spark has issues only under acceleration. I worry that you are not getting a good evaluation from the shop. It could be the cv but a new (rebuilt)axle would be 80-120 bucks and the job could cost ~150-200 labor. Don’t replace the mounts for this issue unless they are really messed up which the mech should have seen the first time.

It’s the same shop but a different mechanic. The one who did the initial diagnosis has been replaced. The spark plugs and catalytic converter were replaced about 2 months ago when the check engine light came on. The car runs great with the exception of acceleration in right turns. Straight or to the left is fine. Would you suggest trying just the cv joint first or should I get a second opinion?

I have been having a similar issue recently in a Ford Escort, and it began immediately after having new axles (where the CV joints are) installed. It was terrible, esp turning left and under moderate acceleration. I went back and the driver’s side axle was swapped out. That solved most of it, but once the really bad stuff was gone from the driver’s side, it just made the milder problem on the pass. side more noticeable. I can’t tell you what replacing the pass side axle will do yet b/c I won’t be taking it back until Tuesday. I can let you know.

In the middle of trying to get this cleared up a mount was replaced, but it did nothing but tighten up the vibration a bit.

But, either way bad joints can cause this - in my case actually defective rebuilds.

At 90K if those are the original axles, then it wouldn’t surprise me a bit if you need new ones.

Thanks for the help. I am going to bring it in on Monday and get a better explanation of why the mounts were missed on the first inspection.

I would still worry about the CV joints though. But this can be hard. The typical way to find that a CV joint is bad is via sound. It was hard for me to convince the mechanic that the new axles they had just installed were screwy.

There is some leaking around one of the inner cv joint boots so we are definitely going ahead with that repair. I’m questioning the mounts because they were found to be OK on the first inspection and according to Euryale1 above this should not have been missed. The mechanic believes the combination of inner cv joint and two bad mounts is what is causing the vibration. Hopefully I won’t run into the same defective replacement problem that you did.