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Old 06-26-2021, 05:21 PM
Leonardp59 Leonardp59 is offline
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Default Shaking

I have a technical question I’m hoping for some help with. I have a 68 convertible that it’s back on the road after 31 years. The car has 42,000 original miles. I’m experiencing vibration and shaking between 40 and 45 mph and intermittently at other speeds. I’ve had the wheels balanced and I put new upper and lower ball joints and tie rods on both sides. I’ve got an appointment to get the front end aligned the first of this week. Anybody have any ideas about why I might be having this problem? Thanks

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Old 06-26-2021, 05:27 PM
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If the tires are old you may be getting tread separation. Modern tires have an additional nylon or rayon ply to prevent this. Check for cracks, blisters, and out of round.

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Old 06-26-2021, 05:31 PM
Leonardp59 Leonardp59 is offline
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Forgot to mention it’s got brand new radial tires and 15 inch Rally two wheels

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Old 06-26-2021, 05:37 PM
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Try swapping the tires front to rear and see if it makes a difference. Could still be out of round or a bent wheel but a good tire guy should have spotted that. Does one wheel have more balance weights on it than others ?

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Old 06-26-2021, 05:42 PM
Leonardp59 Leonardp59 is offline
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Honestly not sure about wheel weights. I will ask the guys at the shop on Tuesday when I take it for alignment to check the rims and try rotating the tires. I’ve read it could also be wheel bearings or an idler arm but with such low miles It would have to be a case of some issues with age not mechanical wear

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Old 06-26-2021, 06:55 PM
Goatracer1 Goatracer1 is offline
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Is this a up and down bounce or a side to side shimmy?

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Old 06-26-2021, 07:19 PM
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More like side to side I think

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Old 06-26-2021, 10:38 PM
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Even though they are new one could be bad. It won’t cost you anything to swap tires front to back. If that doesn’t change anything than there must be something loose in the front end and when you align it a good shop will find it

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Old 06-26-2021, 11:09 PM
Leonardp59 Leonardp59 is offline
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Quote:
Originally Posted by Goatracer1 View Post
Even though they are new one could be bad. It won’t cost you anything to swap tires front to back. If that doesn’t change anything than there must be something loose in the front end and when you align it a good shop will find it
Thanks

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Old 06-27-2021, 12:43 PM
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If you feel the shaking in the steering wheel, it's either going to be caused by the tires/wheels or something in the front suspension or steering linkage. Should be pretty easy for a reputable shop to pinpoint slop in the steering if there is any. Agree with starting by swapping the wheels front to back to see if anything changes.

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Old 06-27-2021, 12:43 PM
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You say vibration and shaking.. could driveshaft balance be causing the vibration? Had that happen on mine several years ago. Just an idea..

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Old 06-27-2021, 03:27 PM
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could also put it on jack stands and let it idle in gear to see if a rear axel or rim is bent. Assuming it is a side to side movement..

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Old 06-27-2021, 05:00 PM
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Might check the driveline U joints also while under there, some play or even a tight joint can create a shake especially under throttle.

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Old 06-27-2021, 08:53 PM
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There's a condition convertibles experience called tramping, pretty much nature of the beast. F bodies have "cocktail" shakers installed at the outward corners of the body to try to control it, nothing on A bodies. Its kinda like going over a suttle railroad crossing at an angle at speed. Not sure if thats what you're experiencing but ...

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Old 06-28-2021, 03:37 PM
mgarblik mgarblik is offline
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You have lots of good suggestions in the thread. In order of most likely. Lousy new tire is by far the #1 possibility. Major splice overlap, tread separation, just a poorly made tire. Tire out of round, radial runnout over .045" will make a convertible from this vintage tramp. #2 bent rim. Doesn't take much rim bent over .030" will shimmy in a noticeable way especially in a convertible. Lack of roof structure amplifies everything in the wheel/tire area. #3 Rally II wheels are difficult to balance by someone who doesn't care, is in a hurry, or who doesn't know better. The shape of the formed center of the wheel is not always prefect and a balancer using a cone system to balance can be hit or miss. They balance much better on a machine with a lug-centric adapter plate. Time consuming and more expensive, about $100.00 to balance 4 wheels properly around here. #4 tires have so much tread runnout, they may need to be shaved to make them round if you don't want to replace them. (new doesn't mean good, especially when dealing with tires). #5. If a drum brake car, possibly a drum weight (s) have fallen off and that is the source. You can generally tell if a weight is missing. #6 Wheel alignment. It's possible if the angles are way, way out of spec, you can have the condition you describe, but not likely. Especially if not happening along with a crooked steering wheel or any type of pull condition. Good luck with it.

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Old 06-29-2021, 12:41 AM
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Front wheel bearing preload.

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Old 06-29-2021, 09:44 AM
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You didn't mention what kind of car you have - is it a Firebird, a GTO/Lemans/Tempest, or a full size car? The solution may vary depending on the model.

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Old 06-30-2021, 09:29 AM
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As mentioned, wheel balancing can be misleading if performer by an inexperienced operator or antiquated equipment. I always ask (and pay more) to have wheels and tires run on a "road force" balancer. While not "new", these machines are far more advanced than the old school spin balancer. The idea is to match the inconsistency of a tire with any inconsistency with the rim. In addition, the road force can help determine if a tire or the rim is out of spec.

On an old spin balancer- it will tell you where to put the weights, but the end result can still be an out of balance assembly if the tire and/or rim are out of spec.

And speaking of the person operating the equipment... this past winter I mail ordered a new set of snow tires and rims for my late model Buick. The package included load force balancing. Bolted on the tires and car had bad vibration. Brought to local Goodyear shop and all wheels were way out of balance spec. Fortunately the original retailer covered the $80 rebalance, so I was only out my time and hassle.

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Old 07-27-2021, 04:01 PM
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I know this is a dated conversation but if your Rally 2's are Wheel Vintiques that is the first place I would look. Mine wobble badly on balance machine with the lug centric adapter. Just a thought.

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Old 07-27-2021, 04:32 PM
Leonardp59 Leonardp59 is offline
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Thanks to everybody for the comments. I did have the wheels road force balanced and they are much better now. I’ve also replaced the end links and the transmission mount. I haven’t had a chance to drive it yet is it still in the shop because I ended up ordering a new fuel tank but when I drove it after the rebalancing it was much better although not completely gone

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