Bushes
- Thread starter Biglockie
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Turbo Lag FTW
Hate those none insured you know who types
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They for the back suspension and will they go on the saloon? My bushes are worn as Ive been issued a recommendation slip from its MOT.
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having just changed the front arms on mine i really cant see fitting powerflex bushes being a good idea at all.
The arms pivot on both axis around the bush and the stock bushes are shaped in a specific way. This allows audi to keep good control over the steering and suspension geometry as the suspension and steering moves. Having changed them for polybushes you've completely altered how the bush will respond to suspension and steering input, and you'll probably find the geometry is now no longer correct as polyurethane acts very differently to rubber in compression.
I'd be keeping those bushes on the shelf and refitting them when you get the chance.
The arms pivot on both axis around the bush and the stock bushes are shaped in a specific way. This allows audi to keep good control over the steering and suspension geometry as the suspension and steering moves. Having changed them for polybushes you've completely altered how the bush will respond to suspension and steering input, and you'll probably find the geometry is now no longer correct as polyurethane acts very differently to rubber in compression.
I'd be keeping those bushes on the shelf and refitting them when you get the chance.
having fitted them front and back....if this is how the car's steering and cornering responds when geometry and axis points are changed and/or wrong then perhaps audi should have done it in the first place!
poly bushes completly transform the car.
as I posted when I had them done...
sharper turn in
better steering feel
more predictable loading of the tyres on cornering
removal of vague slip/angle points on over and understeer
less breakaway from rear end on power out of corners
need I go on....
poly bushes completly transform the car.
as I posted when I had them done...
sharper turn in
better steering feel
more predictable loading of the tyres on cornering
removal of vague slip/angle points on over and understeer
less breakaway from rear end on power out of corners
need I go on....
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were you comparing brand new rubber bushes to polys? or did you replace 12 year old rubber bushes with polys?
imo most of the "wow the car handles amazing now" that usually comes with fitting polybushes is more to do with the old ones being totally knackered than the polybushes actually being better.
I had a nice write up by a jaguar engineer about the downsides of using polybushes and how their properties are very different to that of rubber. An example is that rubber doesnt compress, it changes shape, polyurethane has air added to give the desired "softness" and does compress. Rubber bushes also add to the spring rate as they are bonded to the steel housing, polybushes do not as they cant be bonded to steel. In some places on the car they are good, the large rear bushes on the FWD's rear axle for instance are perfect for polybushing as you want to minimise the movement in all directions bar rotational movement which a polybush excels.
On the front suspension of an A4 however theres far too much movement going on to simply say remove the rubber bushes that audis spend millions developing and fit some polyurethane ones that have been knocked together in 20mins by some random company. I havent seen the rear of a quattro, but the rear of a FWD would benefit from them as ive said above.
I'll try and dig out the guys write up.
imo most of the "wow the car handles amazing now" that usually comes with fitting polybushes is more to do with the old ones being totally knackered than the polybushes actually being better.
I had a nice write up by a jaguar engineer about the downsides of using polybushes and how their properties are very different to that of rubber. An example is that rubber doesnt compress, it changes shape, polyurethane has air added to give the desired "softness" and does compress. Rubber bushes also add to the spring rate as they are bonded to the steel housing, polybushes do not as they cant be bonded to steel. In some places on the car they are good, the large rear bushes on the FWD's rear axle for instance are perfect for polybushing as you want to minimise the movement in all directions bar rotational movement which a polybush excels.
On the front suspension of an A4 however theres far too much movement going on to simply say remove the rubber bushes that audis spend millions developing and fit some polyurethane ones that have been knocked together in 20mins by some random company. I havent seen the rear of a quattro, but the rear of a FWD would benefit from them as ive said above.
I'll try and dig out the guys write up.
My bushes were replacing new bushes, I changed them as I changed the suspension and braking as I knew they would not stand up to the increased loads as the suspension allowed.
I agree, poly bushes in some locations are bad.
bushes that provide torsional flex are best left as rubber. ARB bushes for example, when replaced by a non torsional poly bush provides a perfect surface for road grime and grit to get between the ARB and the bush, when the ARB twists it does so against a nice grinding paste. Have seen GTi ARB polished down by a good few mm's due to this.
Bushes that provide lateral flex whether in one of multiple planes are perfect for poly bushing if you require a more predictable or harder compound. Their sole purpose is to provide a cheap boudary between two moving parts that limits road noise and vibration.
you don't find them on any vehicle that requires finely tuned geometry or is in a competitive environment. they use rose joints when required and fixed mounts when not.
no point fixing your castor camber and toe in to find the bushes flexes 2mm and increases all three of those by two degrees under varying loads.
rubber does compress, that is its best quality. It is bonded to steel inserts for both ease of installation and to provide a torsional (vs lateral) axis bush.
the macpherson strut design of the rear A4 quattro is prone to bush flex under load which increases toe out at the rear by a considerable margin. No only does this make steering input vague it wears tyres more quickly.
The spring rate you describe is present in rubber bushes but is not in a fixed plane and also limits the predictability of the steering and suspension when under load.
Don't get me wrong, I think there are some truly dreadful products out there. I fitted a set of Bug pack polys to my Mk2 Gti and some of them were so poorly manufactured they barely fit the holes they were made for. others had not been moulded properly.
however, choose carefully and use companies that not only mould but machine their bushes for correct fitting, fit them correctly using plenty of lube, check and service them regularly and they will transform the handling of any car that has a multi point suspension set up and add significantly to those that have a simpler suspension design.
they are not for everyone though, if you want the Citroen C5 esque "riding on air" feeling....don't do it
I agree, poly bushes in some locations are bad.
bushes that provide torsional flex are best left as rubber. ARB bushes for example, when replaced by a non torsional poly bush provides a perfect surface for road grime and grit to get between the ARB and the bush, when the ARB twists it does so against a nice grinding paste. Have seen GTi ARB polished down by a good few mm's due to this.
Bushes that provide lateral flex whether in one of multiple planes are perfect for poly bushing if you require a more predictable or harder compound. Their sole purpose is to provide a cheap boudary between two moving parts that limits road noise and vibration.
you don't find them on any vehicle that requires finely tuned geometry or is in a competitive environment. they use rose joints when required and fixed mounts when not.
no point fixing your castor camber and toe in to find the bushes flexes 2mm and increases all three of those by two degrees under varying loads.
rubber does compress, that is its best quality. It is bonded to steel inserts for both ease of installation and to provide a torsional (vs lateral) axis bush.
the macpherson strut design of the rear A4 quattro is prone to bush flex under load which increases toe out at the rear by a considerable margin. No only does this make steering input vague it wears tyres more quickly.
The spring rate you describe is present in rubber bushes but is not in a fixed plane and also limits the predictability of the steering and suspension when under load.
Don't get me wrong, I think there are some truly dreadful products out there. I fitted a set of Bug pack polys to my Mk2 Gti and some of them were so poorly manufactured they barely fit the holes they were made for. others had not been moulded properly.
however, choose carefully and use companies that not only mould but machine their bushes for correct fitting, fit them correctly using plenty of lube, check and service them regularly and they will transform the handling of any car that has a multi point suspension set up and add significantly to those that have a simpler suspension design.
they are not for everyone though, if you want the Citroen C5 esque "riding on air" feeling....don't do it
So what ones on the A4 quattro's are best to just be replaced with standard bushes and what with the Powerflex?
How do you service them? Lube them up or just replace them?
Cheers.
How do you service them? Lube them up or just replace them?
Cheers.
I lube them up and force out any crap that has got in between the bush and the metal. poiny nosed grease gun I have for my bike is just the job.
I wouldn;t replace the ARB or ARB drop link (not even sure you can replace those ones actually).
those one have the shaft rotating in the bush.
I replaced pretty much everything else, especially the big meaty ones on the lower arms.
rear lower arms more prone to wear than the top
I wouldn;t replace the ARB or ARB drop link (not even sure you can replace those ones actually).
those one have the shaft rotating in the bush.
I replaced pretty much everything else, especially the big meaty ones on the lower arms.
rear lower arms more prone to wear than the top
