Carl Davey

iTrader: (3)

I've been looking at fabricating some rear drop links for my MY98 Impreza for some time now. Having put some thought into it today and chewing things over with my old man it looks as though using a pair of rose joints either side may be the most feasible way to make these. We are thinking purely from a fabrication perspective.

What i'd like is someone who knows considerably more about Impreza suspension to tell me if having the facility to extend and retract the length of the drop links could have any bearing over the vehicles handling. Having never had a proper look nor seen an Impreza rear anti-roll bar i have no idea if the unit is fixed or pivoted.

I'm currently assuming pivoted and therefore having adjustable links will have pose no true benefit to the fine-tuning of a cars handling?

Alternatively, does anyone have a nice diagram of the Impreza rear suspension setup?

Apple

Have a search for some posts from Ozzy where he fitted his droplinks for an idea of what stuff looks like underneath...

If you have them adjustable then you'll be able to alter how quick the ARB comes in when you go round a corner. I had Powerflex ones on and they seemed to be approx 10mm less between centres than the OE ones. Shorter hole centre distance = quicker effect as you're preloading the ARB more (you're not changing its stiffness as this is a function of the ARB tube diameters)

One think to bear in mind with using rose joints, unless you put some kind of compliant bushing in the holes, you'll add to the general noise / vibration / harshness of the ride as you've made a direct, solid connection through which to transmit the road imperfection etc. The OE droplinks rely on the plastic giving a little, Powerflex ones have polymer bushings and I think Whiteline ones have the same AFAIR. It's designed to be stiffer than the OE setup but still allow some cushioning. Also, it allows for some misalignment on assembly etc. You could get some with rose joints but they're less forgiving.

Another consideration with rose joints is the material selection to withstand corrosion from the general road krud / salt etc and also fretting wear from small amplitude oscillations - once they wear and open up a gap, they'll get grotty. At a guess, you'd want some with wiper seals and long life materials (stainless steel may not be the best even though it resists corrosion more). I designed a test rig for work and stainless rose joints couldn't hack the endurance testing, AFAIR we settled on brass or bronze and these seem better but get some advice from a supplier - preferably that understands the application...

HTH

Andy

bob

keap_scooby

carl,

in the new 2005 demon tweeks cat, it has whiteline droplinks for the impreza using rose joints and adjustable.

alan

Carl Davey

iTrader: (3)

Could you elaborate on this a little more for me please Andy? I don't understand how it will be possible to pre-load the ARB. If the ARB pivots on it's own bushes (which it appears to do from Bobs pic) then how can pulling it closer to the lower arms affect how it performs? I agree and understand that the rigidness of adjustable drop links will carry the same benefit as solid versions.

I think there's always going to be a compromise made when using rose joints over rubber/polyurethane. Amplified road noise and reduced life expectancy is part and parcel as far as i am concerned. It can be mitigated against through choice of joint but at the end of the day there is no solution as such.

Alan, just had a nose through the DT catalogue, the Whiteline ones were virtually exactly what i had in mind, cheaper than i'd imagined too. No fun in buying them though is there?

Apple

I'm thinking about it...

I remember a link which describes the action of the ARB so I'll try to find it...

StickyMicky

how does it preload the ARB

maybe if one side was longer then the other??

vindaloo

Changing the length of the links will affect the operation of the bar but I'm struggling with my Inglish to describe it properly.

Assume that normally, the link pushes straight down (90 deg or perpendicular) on the bar. The bar is deflected one inch for every inch of travel at the suspension end of the droplink. There's no movement in any other direction.

If the link is shorter or longer, then it changes the relationship between the way the bar deflects relative to the suspension end of the droplink. E.g. The suspension end of the droplink moves one inch down but that is translated into a lesser deflection of the bar as it is no longer perpendicular. The drop link moves in more of an arc rather than a linear deflection.

Best example of something similar I can think of would be the rear suspensions on some Citroens and Peugeots. The shock absorber mounts in such a way that the movement of the shock absorber piston is far less than it would be if the mounts were the same distance from the pivot of the trailing arm.

J.