[Staowners] SCUTTLE SHAKE REVISITED

[terry poole]

PS  -  With apologies and condolences to Bob Hamilton and his coupe!




On 12 May 2008, at 19:15, terry poole wrote:

> I agree!
>
> Simple then - buy some round tyres and get your wheels balanced  
> properly.
>
> What a relief!
>
> Terry.
> On 12 May 2008, at 15:35, CotaLymepond at aol.com wrote:
>
>> Ah  Heck ... here's my 5 cents worth
>>  Scuttle shake is when we see the front portion of our cars  
>> vibrate. (if you really want to experience this phenomenon, go for  
>> a ride in an old T-series MG)  The body on a roadster is somewhat  
>> flexible by design, throw in 60 years of wear and tear, a little  
>> rust, and squashed out body mounts and the cowl (American-ese for  
>> scuttle) will certainly shake around a bit. This is to be expected  
>> on a rough road, However if this problem is experienced on smooth  
>> flat pavement, and only at a certain speed then it has to be a  
>> result of harmonics, a magnification of vibrations from a rotating  
>> mass, most likely the wheels and tires, or an out of balance  
>> driveshaft. If running the car up on blocks doesn't duplicate the  
>> problem then the imbalance is probably in the front wheels.  
>> (although if the rear axle is sitting on jackstands, then an  
>> imbalance in the rear might not gain resonance as the flexibility  
>> of the tires would allow the axle to vibrate, whereas the axle  
>> sitting firmly on stands would prevent the harmonics from getting  
>> started and building on itself.)
>> The reason sedans don't experience this is because the roof  
>> structure ties the cowl into the rest of the body and the whole  
>> body would have to shake as one unit, which would not seem as  
>> evident from  the drivers seat.  If the problem was related to the  
>> engine shaking through the motor mounts, then the problem would be  
>> evident at certain engine RPM's, regardless of the vehicle's speed.
>> It seems that the most likely cause is an out of balance tire, or a  
>> bent wheel, or just an out of round tire, (very common on belted  
>> tires, even when they're new) I would be willing to bet that if one  
>> of these cars with severe scuttle shake was fitted with a set of  
>> new balanced radial tires, the problem would go away?
>> Just my thoughts <> Steve Cota <>
>>
>>
>>
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