Poly bushes, good or bad?

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Thu 27 Mar 2014 07:58
Poly bushes, good or bad? - pullgees

I've put them in my rear suspension trailing arms but am now wondering if I've done the right thing. The original bushes were rubber incased in a metal body, because they have a softer material they act as a dampener.

The poly ones feel harder at the rear when driving . Could they cause damage else where in the suspension?

The only reason I fitted poly bushes is because ther are ten times easier to fit than the OEM ones.

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Thu 27 Mar 2014 08:51
Poly bushes, good or bad? - skidpan

Easy to fit (as you say) but much harsher.

Would they damage your car, doubt it, the spring takes all of the hits.

But would I use them on a road car, personally no unless my name was Barry and I drove a Saxo.

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Thu 27 Mar 2014 09:51
Poly bushes, good or bad? - veryoldbear

Done on last SAAB 95 estate and they were excellent.

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Thu 27 Mar 2014 13:52
Poly bushes, good or bad? - pullgees

Barry and his Saxo haha!

Okay thanks that reassures me

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Thu 27 Mar 2014 17:04
Poly bushes, good or bad? - corax

It depends on the car. I had Powerflex fitted to the front wishbones and trailing arms on my previous BMW.

With hindsight, I would only do the front wishbones. Too much harshness on the rear, losing the refinement that BMW are known for.

Worth it on the front for the extra accuracy in the steering and I didn't notice much extra harshness.

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Thu 27 Mar 2014 17:32
Poly bushes, good or bad? - pullgees

It depends on the car. I had Powerflex fitted to the front wishbones and trailing arms on my previous BMW.

With hindsight, I would only do the front wishbones. Too much harshness on the rear, losing the refinement that BMW are known for.

Worth it on the front for the extra accuracy in the steering and I didn't notice much extra harshness.

Mine's a Fiesta. The trailing arms are much stiffer now I fail to see how the spring and shockabsober can compress, but Im no expert on suspension. Presumably the spring must still compress otherwise the rear would be rigid, effectively suspensionless , but this cannot be so.

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Thu 27 Mar 2014 20:19
Poly bushes, good or bad? - Mike H

Done on last SAAB 95 estate and they were excellent.

Dono on current Saab 9-5 estate and ditto! But I have heard that firstly, different makes of poly bushes have differing levels of harshness and, and secondly, using them in the wrong places within the suspension can cause unbearable harshness, requiring their removal.

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Fri 28 Mar 2014 08:48
Poly bushes, good or bad? - skidpan

Mine's a Fiesta. The trailing arms are much stiffer now I fail to see how the spring and shockabsober can compress, but Im no expert on suspension. Presumably the spring must still compress otherwise the rear would be rigid, effectively suspensionless , but this cannot be so.

Springs and dampers move up and down by several inches. Poly bushes are fitted to wishbones etc where the rotation of the bush is only a few degrees even at full movement. The harshness is simply the fact that the bush is much stiffer and allows less movement within the bush than the original rubber. But the rest of the suspension still works as the designer intended. You will still get the exact same compression of the springs.

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Fri 28 Mar 2014 12:23
Poly bushes, good or bad? - pullgees

Mine's a Fiesta. The trailing arms are much stiffer now I fail to see how the spring and shockabsober can compress, but Im no expert on suspension. Presumably the spring must still compress otherwise the rear would be rigid, effectively suspensionless , but this cannot be so.

Springs and dampers move up and down by several inches. Poly bushes are fitted to wishbones etc where the rotation of the bush is only a few degrees even at full movement. The harshness is simply the fact that the bush is much stiffer and allows less movement within the bush than the original rubber. But the rest of the suspension still works as the designer intended. You will still get the exact same compression of the springs.

I can't see how there can be any movement in a polybush as they are solid. Surely it would takes tons of weight for the retaining through bolts to compress the material. Is it possible that the bush housing of the trailing arms can slide around the bush when the rear end of the arms (where the suspension is) is lifted by the springs? As I say I'm not knowledgable on this matter, just asking

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Fri 28 Mar 2014 18:25
Poly bushes, good or bad? - skidpan

I can't see how there can be any movement in a polybush as they are solid

The ones I have fitted have a steel bush that fits down the centre after the 2 halves have been pushed into the wishbone. This allows the wishbone to move as designed but without the compliance of the softer rubber bush.

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Fri 28 Mar 2014 23:47
Poly bushes, good or bad? - pullgees

I can't see how there can be any movement in a polybush as they are solid

The ones I have fitted have a steel bush that fits down the centre after the 2 halves have been pushed into the wishbone. This allows the wishbone to move as designed but without the compliance of the softer rubber bush.

Ah so the steel insert acts as a bearing and some rotation occurs around it. If this is the case then the sides of the bush must be wearing against the inside of the mounting bracket., which seems a bit crude.

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Sat 29 Mar 2014 09:03
Poly bushes, good or bad? - skidpan

Ah so the steel insert acts as a bearing and some rotation occurs around it. If this is the case then the sides of the bush must be wearing against the inside of the mounting bracket., which seems a bit crude.

Do you not think that the designers considered this when specifying the material they use.

Being an aftermarket "performance" product they will never last as long as OEM bushes (despite what the makers say) but at least they are easy to swap and come in nice colours.

If you are worried why not simply swap back to OEM bushes.

With regards to your car being a Fiesta we had a Puma, same suspension. The wishbone bushes needed replacing and it was the same price to buy a new wishbone with bushes fitted (and a new bottom joint) as it was to have new bushes fitted to the old wishbones (no new bottom joint). It was a no brainer.

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Sat 29 Mar 2014 11:51
Poly bushes, good or bad? - corax

Being an aftermarket "performance" product they will never last as long as OEM bushes (despite what the makers say) but at least they are easy to swap and come in nice colours.

I thought that one of the reasons to use them is that they last longer than the original bushes because they do not degrade like natural rubber, although I never had a car long enough with polybushes to find out.

Your tyres are meant to last longer because the poly bushes keep better alignment while cornering. This might be cancelled out due to pushing the cornering abilities though!

I had fun driving my BMW with its polybushes, Eibach springs and Bilsteins but it did lose its good ride.

After years of modifying suspension I now keep things standard unless an aftermarket product really improves an original poor piece of design. Getting old and my back won't take it any more :)

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Sat 29 Mar 2014 16:56
Poly bushes, good or bad? - pullgees

Ah so the steel insert acts as a bearing and some rotation occurs around it. If this is the case then the sides of the bush must be wearing against the inside of the mounting bracket., which seems a bit crude.

Do you not think that the designers considered this when specifying the material they use.

Being an aftermarket "performance" product they will never last as long as OEM bushes (despite what the makers say) but at least they are easy to swap and come in nice colours.

If you are worried why not simply swap back to OEM bushes.

With regards to your car being a Fiesta we had a Puma, same suspension. The wishbone bushes needed replacing and it was the same price to buy a new wishbone with bushes fitted (and a new bottom joint) as it was to have new bushes fitted to the old wishbones (no new bottom joint). It was a no brainer.

No not worried, as I said I'm just trying to understand how they work.

I'm not talking about the wishbone or lower arm, I already said way above that the job was on the trailing arms or rear axle beam as Ford calls it.

Am I right in saying that the outside of the bushes rubs against the inside of the mounting bracket when the bushes rotate? If that is the case, you are right they won't last as long as OEMs.

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