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[Marks DTM Calib]

I have no worries about the front poly bushes or any of the dimension.

If you look at the design and layout, the forces they see are mainly in the horizontal plain and the movement is rotational around the centre line of the bush, all good and the wish bones will see no increased stresses as a result of the polys being fitted in fact, all the polys do is stiffen up the connection to the subframe so the only potential point of stress increase would be here (and its built like a brick out house so absolutely no worries).

The rears are different, due to the sub frame and suspension design the bush is vertical and has to be able to withstand a rotational movement which is perpendicular to the centre line of the bush. Make this one stiff and you increase loadings on the wishbone significantly. Every time the suspension leg compresses/expands the flex in the wishbone will be much greater than designed and the result will be fatigue and consequentially failure.

[05omegav6]

No John, the plod one

Not a question of keeping on fitting them, they've been on the car since Jan/Feb '14, as a long term test... But I totally agree that if two completely different approaches to these rear bushes both result in the same failure mode, then this obviously isn't the solution that was hoped for. Any other solution is likely to demand a reworking of the rear mounting on the subframe, and in the words of Peter Jones, I'm out.

On the plus side, something hasn't been tested properly until it has been tested to destruction

[05omegav6]

I have no worries about the front poly bushes or any of the dimension.

If you look at the design and layout, the forces they see are mainly in the horizontal plain and the movement is rotational around the centre line of the bush, all good and the wish bones will see no increased stresses as a result of the polys being fitted in fact, all the polys do is stiffen up the connection to the subframe so the only potential point of stress increase would be here (and its built like a brick out house so absolutely no worries).

The rears are different, due to the sub frame and suspension design the bush is vertical and has to be able to withstand a rotational movement which is perpendicular to the centre line of the bush. Make this one stiff and you increase loadings on the wishbone significantly. Every time the suspension leg compresses/expands the flex in the wishbone will be much greater than designed and the result will be fatigue and consequentially failure.

The original bushes I used were soft enough to allow full movement of the wishbone in its normal range, but lacked the strength to support the arm against braking and steering forces causing some odd traits during braking and cornering. The second set were much firmer, but required no more force to fit the ball joint to the strut than the factory ones.

[Marks DTM Calib]

What you need to think about is the construction of the genuine bushes, they are a rubber with an internal pocket and shape which means they remain stiff but, can absorb shock loading, polyurethane simply can not do this 

[Andy H]

What you need to think about is the construction of the genuine bushes, they are a rubber with an internal pocket and shape which means they remain stiff but, can absorb shock loading, polyurethane simply can not do this 

The optimum would be some kind of ball joint that allowed zero lateral & longitudinal movement but permitted the arm to hinge up & down.

The genuine rear bush that I cut open had a ball formed half way along the steel centre bush and the rubber formed around it. Given the small space available it is going to be very difficult to come up with something that works better than the genuine VX part.

[05omegav6]

Indeed... Pattern ones are a broadly similar design to the originals.

[deviator]

Whilst not directly relevant here, the Powerflex Black bushes are for the track. Even PF say they are far to stiff for road use.

[terry paget]

I do not understand the thinking behind the vertical rear bush. Common sense tells me it should be horizontal and in line with the front bush - that would achieve a maintenance free lower wishbone, controlled by the MacPherson strut. Are rear vertical bushes common on other cars? Is there any paper explaining the wisdom, or even the point, of the vertical rear bush?

[Mr Gav]

I do not understand the thinking behind the vertical rear bush. Common sense tells me it should be horizontal and in line with the front bush - that would achieve a maintenance free lower wishbone, controlled by the MacPherson strut. Are rear vertical bushes common on other cars? Is there any paper explaining the wisdom, or even the point, of the vertical rear bush?

That's exactly what I was thinking, the Senator had this arrangement but the horizontal bush was at the rear but I always wondered why it didn`t have two horizontal bushes.

[05omegav6]

Whilst not directly relevant here, the Powerflex Black bushes are for the track. Even PF say they are far to stiff for road use.

Presumably because most people would find the NVH levels unacceptable 

[Rods2]

Glad you are okay, as that is the most important when things go wrong, that we get away with it.

I guess you won't be needing any laxatives for a week or two.

[X30XE]

I do not understand the thinking behind the vertical rear bush. Common sense tells me it should be horizontal and in line with the front bush - that would achieve a maintenance free lower wishbone, controlled by the MacPherson strut. Are rear vertical bushes common on other cars? Is there any paper explaining the wisdom, or even the point, of the vertical rear bush?

That's exactly what I was thinking, the Senator had this arrangement but the horizontal bush was at the rear but I always wondered why it didn`t have two horizontal bushes.

To stop the wishbone moving backwards under braking. How else are you going to achieve that? 

[X30XE]

I have no worries about the front poly bushes or any of the dimension.

If you look at the design and layout, the forces they see are mainly in the horizontal plain and the movement is rotational around the centre line of the bush, all good and the wish bones will see no increased stresses as a result of the polys being fitted in fact, all the polys do is stiffen up the connection to the subframe so the only potential point of stress increase would be here (and its built like a brick out house so absolutely no worries).

The rears are different, due to the sub frame and suspension design the bush is vertical and has to be able to withstand a rotational movement which is perpendicular to the centre line of the bush. Make this one stiff and you increase loadings on the wishbone significantly. Every time the suspension leg compresses/expands the flex in the wishbone will be much greater than designed and the result will be fatigue and consequentially failure.

If the crush tube isn't long enough the poly 'shoulder' gets pinched between the wishbone and the chassis which causes it to grip the wishbone.  Admittedly not to the extent of fitting a solid poly to the rear, but still far from ideal.  There's a video on youtube somewhere showing someone else's poly with a chamfered shoulder which doesn't do this ( more like the OE fitting).

[05omegav6]

I do not understand the thinking behind the vertical rear bush. Common sense tells me it should be horizontal and in line with the front bush - that would achieve a maintenance free lower wishbone, controlled by the MacPherson strut. Are rear vertical bushes common on other cars? Is there any paper explaining the wisdom, or even the point, of the vertical rear bush?

That's exactly what I was thinking, the Senator had this arrangement but the horizontal bush was at the rear but I always wondered why it didn`t have two horizontal bushes.

To stop the wishbone moving backwards under braking. How else are you going to achieve that? 

Eh? Have you looked under a Vectra C?

[X30XE]

Nope. I'm not poor