The AUSubaru.com.au Forums

am considering using wrx rack in brumby crossmember. with the wrx hubs and brakes and struts or coilovers and lseries lower arms. brumby will be lowered around 4". with the wrx rack being longer will this adversely affect bump steer? i know that tie rods need to be shortened somewhat. my thoughts are that standard is bump out (toe out on bump) on compression and rebound is bump in, and after mods there will be less compression bump out, which is good but more rebound bump in. am i missing something.

I think you are confusing toe adjustment (in/out) with bump steer which is a different thing .

You get bump steer when the steering racks inner spherical joints are not at the same height (or distance apart) as the control arms inner locating points - on the cross member .
The reason being that if the heights are different the control arms and tie rods scribe different effective arcs which causes toe angle change as the suspension moves through its full travel .
If the control arms and tie rods scribe the same effective arc the toe angles shouldn't change .

A .

discopotato03 wrote:You get bump steer when the steering racks inner spherical joints are not at the same ... distance apart as the control arms inner locating points

...which is exactly what you get putting the lib/impreza rack in an MY. Many people seem to have done it without complaint, but it's not something I would do. I have cut down a Lib crossmember to get around this problem. Haven't finished it yet, so I can't tell you how it drives....

Yes , caught between a rock and a hard place with the MY cross member .
You may be better off looking at an MY power rack and see what you can do about tie rod and tie rod end lengths .
Its a shame that Subaru made the steering arms part of the knuckle casting because altering their lengths would have changed the effective ratio .

Is there any chance that a modified L Series front cross member would be a better bet in an MY ?

A .

have chopped the rack mounts out of my member and grafted the liberty ones in. i think it will be ok. i dont think is any advantage with cutting lib one point. you still end up with a rack that is too wide, unless you shorten rack as well.

we shall see how we go. thanks guys

it's not the rack mounting points that are the problem, it's the distance between the inner control arm pivots.

My Brumby now has the Lib struts, hubs, control arms, rack, and crossmember, so it has the same front track as the Lib. If I had kept the MY crossmember I would have used an MY power steering rack with longer tierod ends and L series control arms.

Point wrote:it's not the rack mounting points that are the problem, it's the distance between the inner control arm pivots.

My Brumby now has the Lib struts, hubs, control arms, rack, and crossmember, so it has the same front track as the Lib. If I had kept the MY crossmember I would have used an MY power steering rack with longer tierod ends and L series control arms.

What will you be doing for the rear track? Or will you leave it so the front is wider than the rear???

Cheers

Bennie

I haven't planned to alter the rear track as yet. I may have to if it causes problems, but I've done similar things to Datto rally cars before without any problems. I will see where the wheels sit when I get the crossbred kit for the rear...

i see why they call you point!
i think my engineer would drop his jaw if i rolled up with full liberty front, but only major mods are mounts for rear of arms, so good thinking on your part.
if i pick my ride height carefully, control arms down a bit, tie rods up a bit from horizontal, with a bit of measuring it will be ok.
rear cant be that hard at worst you can just run spacer plates. or change offset on rear rims. plenty options
do we reckon we can taper ream lseries arms to suit liberty ball joints. must look at angle to cut. i think reamers are 12degrees or is that a morse taper.

crossbred have the tool to ream out the L control arms, so I'd talk to them first.

to use the lib front end you'd have to lift the car at least 2" or cut huge holes in the chassis rails where the rear of the control arms mount, and i see you are planning on lowering it...

my engineer is a good mate of mine so he's quite used to my weird conversion ideas :P

I've never seen an MY and an L Series front cross member side by side but my guess is that they are more closely related than an MY and an early Lib one .

I think you'd save yourself a lot of work by using an MY power rack - unless you are hell bent on moving the control arm locating points . Factory engineering is often hard to beat on price and in this instance the only disadvantage is possibly the MY racks ratio .

IF the L cross member falls in with its power rack you may get the chance to gain a few geometry improvements . Also the early basic Lib rack has a slightly faster ratio than the L and are like grass seeds .

Be a little wary of lots of track increase because there are legal issues involved . Also note than when you go to Lib/Imp struts you get a degree of camber adjustment via cammed clamp bolts between the struts and the knuckle or upright if that's what you call it .
Another prob with widened track is drive shaft length , the best factory shaft to use would be an XT6 one but none here .
Lack of positive caster is the real downfall in most Subaru's but it can be adjusted out partially with adjustable strut tops .

Also some things to note when lowering by substantial amounts .

Because the car sits further down in its range of suspension travel the outer ends of the control arms are higher in relation to the inner ends . If the outer ends become higher the effective length of the arms shortens which pulls the strut feet inwards increasing positive camber .
Also with the control arms more towards horizontal the radius rod angles change which affects anti climb/anti dive characteristics .
Lastly the closer the body gets to the bump stops the higher the spring and damper rates need to be to stop the car bottoming out - or running to the limit of compression travel .

Being lower may give the Roger Racer look but it doesn't guarantee good handling . If it were me I'd be finding ways to increase roll stiffness (bars/springs) and improve the suspensions geometry at near the std ride height .

You might find it a lot easier just to buy an early Rex because they come with much of what you want std . If you left the Brumby std you have both bases covered .

A .

onya potato, you make some excellent points and you get me thinking. got some coilovers coming so hope i have enough adjustment. might make a toe guage and see what we get
got a wrx already, but want lighter and a ute

From what I've read the MY crossmember is narrower than the L's but the lower control arm mount is in the same place, which would mean the steering rack would be about the same width between the L and the MY. If you can get an MY powersteering rack (any touring wagon will have one) then stick with that

Cheers

Bennie