[Healeys] Suspension bushings

[Larry Varley]

Absolutely agree with Michael here, from past experience I would 
completely avoid urethane for any car to replace original rubber bushes. 
Its a pity that the correct rubber bushes are not made, but I would 
still use the reproductions rather than urethane. From an engineering 
standpoint urethane has a totally different way of operating to what the 
car was originally designed for, stretching rubber fixed against steel 
surfaces is not the same as rotating urethane on a pin. Has anyone ever 
asked any of the urethane bush manufacturers if their products are 
approved by current auto manufacturers, or if they will accept liability 
for any damage they will cause? I would prefer to stay with a product 
that is as close as possible to the original specification. In closing, 
enlighten me, do any current auto manufacturers use urethane as their 
standard suspension bush?
Cheers
Larry Varley

On 22/10/2015 7:08 AM, Michael Salter wrote:
> Bob,
> I suspect that I'm not telling you anything that you don't already 
> know here BUT:
> I think the critical point is that the original suspension bushes work 
> in the same way that rubber engine mounts are designed to work. The 
> steel mounting plates (or in the case of mounts steel tubes) are 
> rigidly attached to parts that move relative to each other and that 
> movement is accommodated by the flexing of the rubber medium bonded to 
> each plate.
> The plastic bushes work more like bearings in that the rotational 
> movement is accommodated by rotation of the bolt (shaft) within the 
> bush (bearing). All very well while you are flying straight and level.
> The problem, as I see it, is that when angular displacement is 
> required, as in body roll, the plastic bushes must distort and as the 
> plastic is by necessity relatively rigid, when compared to the 
> original rubber, the loads imparted to the mounting points will be 
> substantially higher than that for which they were designed.
> Maybe you will get away with it, maybe you won't., I just don't want 
> to be passing you in the opposite direction if you don't!!!!
> Michael S
> BN1 #174 (All rubber bushes :-))
>

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