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Polybushes.....worth it?


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Guys,

I'm thinking of fitting a full Polybush kit to my Defender 90 300TDi, as I have been told that they are great.

Should I go for the Polybush brand name, or the considerably cheaper Deflex bushes? I am told that the orange kit will transform the ride a treat. I have just fitted a set of De Carbon gas shocks with standard LR springs, and an Old Man Emu steering damper, and it feels great, but is it REALLY worth doing the bushes?

Is there another brand I should think about?

My Landy is my everyday car, used mainly on road unladen, with the occasional greenlane & ford chucked in. My ultimate goal is the expedition prep'd route for jaunts across Europe & Africa.

Thanks in advance.

Martin

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I have Deflex - I _hate_ them. Too harsh, poor manufacturing standards (mold flash, size tolerances). If it wasnt such a pain to change them, I would take them off an shove them up the ass of the person at Rovers North that recommended them. They described them as having the same density as the blue polybushes (supposedly the same as OEM rubber) - that description was totally wrong.

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Been checking a lot of posts on this as I'm looking to do my bushes.

Many are coming down on the side of the OEM bushes, cheaper and last better than cheap polybushes etc. The only polyurethane bushes worth going for it seems are Super Pro but the cost is about 4-5 times more than cheaper brands. You can but them individually or part sets, I'll probaly just do the radius arms in them. They claim that each bush location is a different density material rather than same for the lot so give better handling and performance.

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Like others have said, stick with OEM bushes. I have taken my Discovery to numerous places (Morroco, Russia, Libya, Australis etc) and I have always used OEM bushes. Mine seem to last really well the car is now 16 yrs old and I am looking at replacing all the bushes when I get back from Spain. The current set have been on for over 4yrs.

HTH

Ivan

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I have Deflex - I _hate_ them. Too harsh, poor manufacturing standards (mold flash, size tolerances). If it wasnt such a pain to change them, I would take them off an shove them up the ass of the person at Rovers North that recommended them. They described them as having the same density as the blue polybushes (supposedly the same as OEM rubber) - that description was totally wrong.

Hi Mate

Loved your reply, could almost feel the anger! :D

You may have made my mind up to go OEM.

Sorry you are stuck with something that costs time and money and doesn't do as it said on the tin! :angry:

Cheers

G

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There was a very nice post on E30zone regarding these polypushes and the bloke makes some very good points as to why they should be kept standard!!

im quoting here as they dont allow guests to view their forum:

So poly bushes are great right? I’m not part of the motorsport scene so I don’t understand why they’ve become so popular. They seem to be sold on the pretence of being stiffer so the car is tighter and that must of course be better…

The merit of poly bushes has to start with the material, which is polyurethane, and how it compares to rubber. The base material offers better isolation properties than rubber because of its damping characteristics. Rubber increases its stiffness dramatically the faster you push it, or vibrate it, but it also has comparatively low damping for large, slow amplitudes. Polyurethane is better for this so controls larger amplitudes better and also transmits less vibration at higher frequencies. As a material it would be ideal to be used in place of rubber as it gives the option for improved isolation. This leads me to a question: if the advantages in the material are all about vibration and isolation then why is it sold as a stiff race upgrade?

Polyurethane is also compressible where as rubber is not. By this I mean its volume gets smaller where as rubber just changes shape when you squash it. It contains tiny air bubbles that allow this and the amount is measured by the density of the material. So stiffer polyurethane contains less air and would be of a higher density. Poly bushes as they are designed are very stiff in a material sense I think, almost as though they have no air.

So as a material everything seems positive but it has a rather fundamental flaw in that it can’t be bonded to anything. This means it can only give stiffness in one direction – when you squash it. Rubber on the other hand bonds to metal quite readily so it can give stiffness in both compression and in shear (when you try to push it sideways off a bit of metal it’s stuck to). This is normally in the ratio of 5 to 1 I think off the top of my head, it’s five times stiffer in compression than shear. But this can be manipulated so you can play tricks with metal form both for the inner and outer metals of the bush to control the stiffness as you want. Rubber bushes also give stiffness in a rotational sense as they are acting in shear in that direction too.

1. poly bushes can’t provide rotational stiffness. Take a car and replace all the rubber with poly bushes and its wheel rates will be softer. Rubber bushes contribute on average about 4N/mm at the wheel I reckon, this can differ wildly depending on platform though. 2. poly bushes can’t rely on shear to provide stiffness axially (along the direction of the bolt if you get what I mean) so have to have material around the sides that is compressed too. 3. poly bushes can’t do either of these things yet the suspension still needs to rotate against the compressed material so you get lots of friction. Well you can just fill that full of grease – that will last for ever. 4. poly bushes can’t provide the same amount of pre-compression as rubber because of this friction. By this I mean squeezing an amount of material into a small hole – it could mean poly bushes are actually initially quite soft and need load to stiffen up 5. depending on the platform you could be completely mucking up the suspension dynamics in terms of compliance steers and so on. The bmw suspension is a very good example as the rear trailing bush controls the amount of rear steer you get, fitting a poly bush changes this so the car could actually build lateral acceleration slower than it did before.

So in my opinion the technology is completely flawed and as an engineer I’m not comfortable with that. Certainly on the more advanced platforms where the wheel compliance behaviours are carefully controlled you could be making the car worse. And it will have more vibration as the material is so stiff.

You’ll only find polyurethane in two places on most production cars (well three on Jaguars…) and that is for bumpstops and spring isolators as both suit the material properties perfectly.

There are a lot of people that have seen a benefit (possibly because they’ve replaced a knackered rubber bush with a poly bush – how many have replaced with a new rubber bush?) and that’s because some cars would suit a stiff bush for the track. Any car with a twist beam rear axle like a mk2 Golf for example. The twist beam is a very cheap way of keeping the rear wheels joined to the car but it has a major problem with compliance oversteer which is controlled by the two bushings. Most modern small cars now have these bushes orientated differently to try to counter act it but you can’t cure it. On track it is better to make this bush as stiff as you can. But it would be better in rubber.

So my question of why it is used is I think answered by the fact that they are much cheaper to make than rubber bushes. A rubber bush needs a lot of tooling and manufacturing cost. If you do feel the need to make a bush stiffer then they are the only option.

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Stick with original. If polybushes were so effin great then the manufacturers would use them, in the same way that if (name your fancy oil additive here) was so great then Castrol or Shell or whoever would stick it in their oils to begin with or if stick on magnets and silly whirly air flow things made out of a baked bean tin made a 20% improvement to fuel economy then manufacturers would all fit them to vehicles :rolleyes:

The only exception that I am about to investigate are polybushes to replace the new type rear lower shock absorber bushes on late model Defenders, because they are rubbish and don't last any time on rough roads. I've got a set of polybushes on order for this particular location so I'll try them and see if they work. If they don't I'l chisel off the bush cups and fit the older type 110 rear shocks with the 552818 bushes.

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The only polybush on my 90 is in the panhard rod. As the quote up there says poly bushes (due to not being bonded to a metal shell) can not provide rotational stiffness, this is a plus point in a panhard rod bush especially in anything with decent articulation which tends to rip the bonded rubber bushes as they can not rotate.

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I agree, stick with standards.

Found polybushes to be eaten away buy the dirt etc getting in between them and the metal surfaces and they just dont like it.

Also, why do we need tighter steering in a land rover on the road. I havent ever planned on racing it around bends.... ;)

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Hmmm.

Seems I will be a voice in the wilderness then!

I fitted genuine Polybushes all round on my RRC 5 years ago, primarily because a number of the std rubber ones were shot, and having been through the series appretiship (SP?) of hacksawing / burning out old spring bushes, didn't feel like replacing like with like.

In the 5 years I have had to replace one panhard rod bush, that is it. The beauty of it was in undoing the bolt, and changing the bush without any presses or hacksaws!

On mud terrain tyres, any difference in NVH is impossible to discern.

Just my tuppence.

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Hmmm.

Seems I will be a voice in the wilderness then!

Make that two... or is it an echo :unsure:

'Genuine' blue polybushes on my '72 Range Rover have behaved well so far (about 18 months) ... got fed up smacking the radius arm bushes out with a sledgehammer every year so decided on something different!

AndyG

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As I mentioned in another thread, I've fitted both OEM and genuine red Polybushes to 110s so I can compare like for like rather than polybushes with old bushes. The OEM bushes were more comfortable (particularly when unladen) and better in rough terrain off road, the polybushes are better when towing trailers or carrying heavy loads. (My trailer loads are usually over a tonne and sometimes much higher, while I carry upwards of 750kg payload - often more.)

I've yet to find any difference in durability.

Fitting wise, until recently I had free and ready access to presses so it wasn't an issue either way. However, my agricultural mechanic has just sold up and retired, so if I can't get access to a press the polybushes might have a slight edge.

I'd suggest seeing if you can find two Defenders to compare - one with recent OEM bushes, one with polybushes and seeing how they are for your specific purpose. As for longevity, well, my only thought there is that in general you get what you pay for so ask what corners have been cut in making cheap bushes?

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I'm glad I could at least steer someone away from Deflex. Certainly the article provides interesting points of comparison between poly and rubber, but doesnt address how anyone would benefit from swapping poly into applications originally engineered for rubber. I will admit, it was very easy to install the poly's, and I might actually try the blue genuine polybushes on the radius arm, and trailing arm to axle joint, but I will go back to rubber as soon as possible for the chassis to arm joints.

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I have Deflex - I _hate_ them. Too harsh, poor manufacturing standards (mold flash, size tolerances). If it wasnt such a pain to change them, I would take them off an shove them up the ass of the person at Rovers North that recommended them. They described them as having the same density as the blue polybushes (supposedly the same as OEM rubber) - that description was totally wrong.

with you all the way on this one jim, my 110 SW had had genuine red polys on for 70k or more and i foolishly changed em for deflex when i changed my radius arms and like you say total bag of cr4p. there's been allot of sense talked about why to stay with std rubber and i can't argue with it but i do like my gen orange polys :)

post-1803-1187483980_thumb.jpg

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had orange ploybushes on a tricked up disco on a past truck and it turned a wobbly mess into something you could throw at corners and survive the exit. also got got orange ones on my 90 but rear radius arm bushes are not liking the amout of artic and are starting to squash out off the sides

i would say the decision is not based on ride but more on putting the things in, if you have a press and hacksaw and blowtorch go for originals as normally whatever was standard was designed to be there for reason or if you think you will be quite heavy on your bushes, competition etc and will need to chnge them reg and have no press then go for the polybushes

i think mr buck still uses oem bushes ;)

cheers

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had orange ploybushes on a tricked up disco on a past truck and it turned a wobbly mess into something you could throw at corners and survive the exit. also got got orange ones on my 90 but rear radius arm bushes are not liking the amout of artic and are starting to squash out off the sides

i would say the decision is not based on ride but more on putting the things in, if you have a press and hacksaw and blowtorch go for originals as normally whatever was standard was designed to be there for reason or if you think you will be quite heavy on your bushes, competition etc and will need to chnge them reg and have no press then go for the polybushes

i think mr buck still uses oem bushes ;)

cheers

Press you should be so lucky.

I've only worked in one workshop that had a press. That was for seven years. All other places we used screwed rod or the vice.

Leaf springs are very heavy. Some are impossible to lift onto a press.........Yes leafs do have Metalistic bushes fittes as well.

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