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Cowl shake? Wobble at 40 mph


cutty collector
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Hi everyone I just purchased my 2nd olds convertible. I noticed a definite light lateral shake in the front end in my first one at about 60kmph( 40 mph ) I attributed that to he fact this things sat on new tires for years without being driven. I sort of got used to it and hadn't thought about it much .But now that I bought a 94 red one to make a matched set (that's what I told my wife anyway)it drew my attention to it again .When I drove the second one I noticed it does it too , though much less pronounced .I think it must be the lack of rigidity in the front end? I was going to replace the tires with something a little more high end or at least have the tires rebalanced they are almost new. The red convertible is a miss matched mix of odds and ends tire wise. I also noticed that when you hit a gravel road wash board it does the same ? The cars are both structurally sound the first one was always garage kept from new and the other one is decent as well .what are you guys experiencing do I have to buy a third one to verify this? lol?

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Tire balance and proper alignment just like any car. My first gen travelled straight and smooth like a bullet at any speed. If you live in a state without safety inspection maybe have a mechanic check the ball joints, wheel bearings and such.

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The alignment is good on both cars .Being a gm tech for 25 years has maybe made me a little more sensitive to this type of thing than most .It does feel like a tire out of round or balance issue in my opinion but balance issues generally do not show up on these cars till about 50-65 mph and it is fine smooth as can be at that speed .I can't say that working on convertible w car alignments was a daily occurrence for me in fact I don't think I ever did an alignment of one of these .we only had 2-3 customers with these cars .Regulars w car were my bread and butter though and I did alignments on them on a regular basis so I do have some serious background here. I was merely trying to get some inputs from some of the other convertible owners as to whether they experience this too? on my 94 it is barely noticeable but the 93 stays at it for a couple seconds as I go through the 40 mph barrier .It is definitely there but goes as quick as it comes and as I said it is smooth as silk after that though maybe a slightly bent rim could be the cause as well but not likely as that usually shows up at lower speed and typically stays to some degree. Just looking for some vert owner imputs .I know in a lot of the initial road test by various magazines there was a mention of this and that is why gm installed the brace at the strut towers I believe this was to address this concern .

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Assuming everything else checks out...maybe a bad axle, or bad engine mounts. Either could potentially push the chassis. 

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The alignment is good on both cars .Being a gm tech for 25 years has maybe made me a little more sensitive to this type of thing than most .It does feel like a tire out of round or balance issue in my opinion but balance issues generally do not show up on these cars till about 50-65 mph and it is fine smooth as can be at that speed .I can't say that working on convertible w car alignments was a daily occurrence for me in fact I don't think I ever did an alignment of one of these .we only had 2-3 customers with these cars .Regulars w car were my bread and butter though and I did alignments on them on a regular basis so I do have some serious background here. I was merely trying to get some inputs from some of the other convertible owners as to whether they experience this too? on my 94 it is barely noticeable but the 93 stays at it for a couple seconds as I go through the 40 mph barrier .It is definitely there but goes as quick as it comes and as I said it is smooth as silk after that though maybe a slightly bent rim could be the cause as well but not likely as that usually shows up at lower speed and typically stays to some degree. Just looking for some vert owner imputs .I know in a lot of the initial road test by various magazines there was a mention of this and that is why gm installed the brace at the strut towers I believe this was to address this concern .

 

The parts I highlighted in bold... The suspension on the Convertible should be the same as any other 1988-1997 Cutlass Supreme and the other 1988-1996 W body cars. The sole exception would be the 95-01 Lumina and Monte Carlo since that car was redesigned and gained a traditional rear strut/spring design in the rear. Other than the strut bar, the suspension was the same.

 

Anyways, if a wheel was bent, it would show at most speeds as you said. You would feel it at a speed as low as 5 in some cases. 

 

What I would think would be causing the shake would be the wheel bearings. Those commonly go on 1st gens, specifically the front ones. That's noticeable at 40mph and it makes an annoying humming noise that goes away when you turn. Next time you drive the verts, listen for that, or just jack the car up and shake the wheels. Left to right usually denotes tie rod issues, up and down denotes the lower ball joint (another common problem on these cars) but it can also be the wheel bearing. If it moves up and down have someone else move the wheel at the 12 and 6 position while you look under the car to see what moves around. 

 

Inner tie rod can also be gone. That happened to me once, I had a pull towards the right, shook that tire and saw it moved left to right. Disconnected the tie rod from the spindle, and when I took it out the hole, the inner tie rod simply dropped. That's how I knew it was time to change it. Once I did that, the vert drove fine, it just needed an alignment (I eyeballed the toe and test drove it to where it would pull the least)

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At the risk of getting too techie I could rule out the wheel bearing .the tires are very suspect though and rotating them is likely the best start. I think I did this initially when I first drove the car but I am not a 100% sure I thing swapping them with the other vert will likely be my plan of attack. That will rule out the wheels and tires. I have seen this sort of thing before it usually Just takes time and effort . I was hoping someone had also noticed this on theirs before. I can tell you first hand when you take these over a rough wash board the lack of rigidity due to missing roof support really shows. Another thing I have done was shut the engine off at 70 mph and coasted down through the vibration with the engine shut down as well as the transmission .This would tend to rule out any parts not turning at that point . The vibration remains so in my mind it almost has to be some of the rolling mass wheel tire bearing axle etc.You guy came out with some very good thoughts thanks for the input .Btw steering tie rod ends inner and outer are tight.will keep you posted

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  • 2 weeks later...

mine had a shake or stumble to it as well...It ended up being and ignition problem, I ended up having a coil changed and the stumble seemed to go away. I'm not sure if you are experiencing the same kind of thing, mine was probably at a certain RPM range and tranny shift.

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sounds like classic belt shift in a tire

 

I agree. My 94 vert had the samething. I just finished having the tires replaced and the shake went away. 

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  • 2 weeks later...
  • 4 weeks later...

thought I should update the root cause ended up being excessive runout on the tires face  not sure if sitting for years was a contributing factor or not

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