Brumby rear suspension - Do tyres/wheels have lateral movement to front or rear

henpecked · Post by **henpecked** » Sun Jan 09, 2011 6:31 pm

having a little scraping on one of the rear guards with the large rims and tyres, on the occasional spoon drain when turning right, not enough to show (shiny !!) on the metal as yet, just a short sudden creak and panel crunch

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so to reduce the amount of additional guard cutting, I need to know how the rear wheels/tyres move laterally as they come up on the suspension travel do they move to the front or the rear of the wheel arch ?

cheers:mrgreen:

brumbyrunner · Post by **brumbyrunner** » Sun Jan 09, 2011 7:52 pm

Yes, or course they do. It's a semi-trailing arm design so the wheel base changes through the wheel travel. I've never measured it but it would be around 3 or 4 inches.

littlewhiteute · Post by **littlewhiteute** » Sun Jan 09, 2011 7:56 pm

henpecked wrote:having a little scraping on one of the rear guards with the large rims and tyres, on the occasional spoon drain when turning right, not enough to show (shiny !!) on the metal as yet, just a short sudden creak and panel crunch .

so to reduce the amount of additional guard cutting, I need to know how the rear wheels/tyres move laterally as they come up on the suspension travel do they move to the front or the rear of the wheel arch ?

cheers:mrgreen:

They move to the rear, the rear suspension swings as a "trailing arm" per side.

RSR 555 · Post by **RSR 555** » Mon Jan 10, 2011 1:48 am

Yep as both above guys have mentioned the swing arm moves to the rear as the weight is increased over the rear. You should also remember to check that the wheels are inside the arches or you may need to "roll" your arches or adjust your bump stops.

discopotato03 · Post by **discopotato03** » Mon Jan 10, 2011 8:50 am

Semi trailing arms scribe an arc with the center being an imaginary line drawn between usually the centres of the inner bushes . I don't know if Brumbys are the same as L Series but if they are some ignoramus decided to mount these bushes not on the same axis I suppose to make the outer bit adjustable .
What this does is force the bushes out of shape as they move and is the reason why using urethane bushes is not a good idea . They don't flex like rubber does and if they overload mounting points they can crack and break - been there done that - but not with a Subaru .

Meanwhile back at the semi trailing arm .
These arms actually work through an arc diagonally outwards from the center line of the car . They will be the most rearwards/diagonally so to speak when they are horizontal and most forwards at the upper and lower limits of the suspension travel .

It was once explained to me that semi trailing arm suspension was sort of half way between live axle performance and real independent suspension . It lost most of the unsprung mass of the live axle differential and each side acts independently but actual geometry change is pretty woefull , and the further it moves from "normal" in either direction the worse the geometry gets .
To cap it all off all these early semi trailing arm Subaru's have short rear arms so the arc they go through is wide meaning massive geometry change . It also means you cant have long suspension travel without unacceptable wheel angles .

A .

littlewhiteute · Post by **littlewhiteute** » Mon Jan 10, 2011 1:03 pm

Brumby is not the same as L series.

Brumby runs a single "trailing arm" per side, front to rear, each side is sprung on a torsion bar.
The bars share a common adjustable centre.

brumbyrunner · Post by **brumbyrunner** » Mon Jan 10, 2011 1:56 pm

A: You might be right about the wheel position with regards to the trailing arm being horizontal but this doesn't happen until full bump anyway. Therefore the wheel is all-the-way back at full bump and all-the-way forward at full rebound.

Gary: The L series and Brumby semi-trailing arm designs are almost identical apart from the spring. They can both handle about 6" of wheel travel before the inner bush deforms too much and you start breaking things. Unlike Disco, I've broken them a fair bit.

discopotato03 · Post by **discopotato03** » Tue Jan 11, 2011 12:42 am

Well I never went out of my way to damage my rear bushes/arms because my L is a daily driver . The only way to keep the rear geometry acceptable was to use larger anti roll bars to limit body roll and dynamic caster/camber change . It makes an L Series much more stable and predictable , much easier to drive safely at what most consider normal these days . Std they are diabolical and MA/MV is even worse , narrower track and even shorter suspension links/smaller radius arcs .

I'm sure I mentioned a while back how my Bluebird when converted from 4 to 5 link (live axle) cracked the floor pan adjacent the rear floor pan and rail mounts when it was was changed from Nissan Sport Stanza rubber bushes to urethane ones .
I remember being in it up on the hoist at the now finished Road and Rally Centre and seeing right through these cracks to the lit floor underneath . Can't remember why I was up there but it was part of the process of removing the live rear end and grafting in R30 Skyline semi trailing arm IRS and its matching R200 diff . In case you didn't know JDM SSS Bluebirds got IRS and while the mounts for the cross member and rear diff mount weren't fitted to the Australian made versions some of the locating holes were stamped in one half of the double skin so its possible to do accurately . You have to weld in crush tubes for the mounting pins though mine had threaded steel mounts carefully chopped out of the rails of some early 6 cyl Datsun . I think the pins were 240K .

The legacy of these conversions is that I don't do them any more , easier to find a car that has most of the goodies std , luv that Lancer .

A .