Custom Steering Rack Mounting

[bigm]

Hey Guys,

Here is the story,

My mx73 had powersteering from factory, i removed it and dodgyily put in a ke70/ae86 steering rack, that doesnt line up well at all. but has done the job for a while now.

Now what i want to do is solid mount the steering rack housing to the cross member for the following reasons
-the current mounts do not line up
-it is a track only car and i want direct steering and dont see the need for bushes

The rack housing will most likely be welded to a piece of steel that then bolts to the cross member for removeability if required. I will be doing the fab myself.

Now my questions here that is a bit technical, Where is the ideal place to mount the rack. things i have considered i have to work with.
-Needs to be centered
-Should move forward than a factory rack would (to reduce bind (its a drift car)

The things i dont know.
-what height do i mount it (in relation to the control arm bolt?)
-how mounting it will affect bump steer/ scrub radius etc

If anyone has any good information to help that would be dandy, Google didn't help much but i plan to keep looking, im asking here for some experience who might know what they are on about :)

I also dont have the original rack (no idea where it went to be honest) so i cant take measurements from that.

[lolwat]

dont you move the rack back, so that the tierods/rackends dont end up inline(straight) with the steering arms/knuckles causing binding???
(thats what the nissan guys do)

[bigm]

if u move the rack back they will bind sooner because the straight line will be achieved with less lock...

[Skylar]

http://www.ae86drivingclub.com.au/dcimages/2/0/2/5/552258.jpg


Ehh, can't be bothered 'splainin'. Ask whatever you don't understand.

Note: Ackerman is only evil in the way of drifting.

[lolwat]

yea i just sat down and drew it up and thought WTF!, i swear thats what loyd smith and beau have done, and others

[Skylar]

Oh and zero bump steer isn't possible while you have a radius rod. You can minimise it by having the radius rod parallel to the ground.

[bigm]

I assume the first picture is when the cars suspension is loaded, if so thats all good.

understand the bindining all good.


the ackerman getz me, is it something i can rectify by the position of the rack or is it to do with the knuckles used?

But that gives me a great place to start thanks man

[bigm]

and can u please elaborate on the radius rod- what it is and just a bit more info?

CHeers

[elda_bob]

Ackerman is on the knuckle. Sorry using Nissan talk.
Rack doesn't affect Ackerman.
I don't know what a radius rod is

[lolwat]

acker man's is in your arms, yes you should be able to get arms that dont have it (T3 do them for ae86/ke's) its pretty much when you turn the inner wheel turns less then the outer one(as one has a greater distance to travel)

[Skylar]

Yeah, picture is when car on ground. It be stupid high if it really looked like that but just trying to say lca length = tie rod length and are at same angle to ground. If they are the same length (in the plane parallel to ground), the car won't have any bump steer anyway so it won't matter whether it's loaded or jacked.

radius rod is just another name for caster rod. and with this, if you're running caster the control arm won't be 300/310mm. You need to account for the distance that the ball joint is forward of the LCA pivot which makes the LCA 'shorter' in that plane.

Ackerman is affected by both rack position and steering arm offset. In drifting where we are aiming for 50 degrees of steering lock ackerman effect stack up and you get huge toe out on the inside wheel which is alright since that wheel is the loaded wheel and there's virtually no load on the inside wheel while drifting. When you let off and the load comes back to the inside front wheel, it won't be at the optimum slip angle and won't be doing much work, especially since static toe out helps cars turn in, decreasing inside turn angle even more than zero toe.

Ehh, just move the rack forward to stop binding, don't worry about ackerman stuffs.

lolwat, it's the other way round, the inside wheel turns more than outside because the inside wheel takes a tighter radius than the outside wheel. This is 100% ackerman. Setting 100% ackerman for one corner doesn't mean it's 100% for another corner though.

[lolwat]

yea thats it, ive managed to say everything back to front tonight (s13 cradle thread thingo too)

TOUCHE" to your sir you know your shit

[Sam-Q]

this is a very tricky thing your trying to do. I don't know the name of the bar that goes across but if the ke70 steering rack doesn't have the tie rod ball joints in the same place as the original joints in the cross bar you have then your going to get hectic bump steer. Also doesn't your car have massively long steering arms? What your doing is very hard to get right and easy to get seriously wrong. I don't want to put you off what your doing but you need a jig off your original steering and the ke70 crossmember with the rack in it or else I just can't see it working out. How did I find out this crap? well with some reluctance:

http://s-86.com/s-parts-ta22rp.html

[bigm]

interesting thanks sam,

The issue is that i do not have the original rack for the mx73 or a ke70 crossmember

might be a idea to get a ke70 crossmember and work with that?

and control arms will be 25mm longer. rose jointed items.

and i realise this isnt easy, but it has to be better than the current set up in their now, and with a bit of research and time taken in measuring, lining up on the actual rack it cant be TOO bad

[Skylar]

The things i dont know.
-what height do i mount it (in relation to the control arm bolt?)
-how mounting it will affect bump steer/ scrub radius etc


I thought, I'd simplify this. You want to put the rack below the lca bolt by the vertical distance between the lca bj and the tie rod end. This depends on how much caster you run. That way you try to keep the lca and the tie rod parallel.

If the rack is shorter than crossmember lca bolt to lca bolt you can space the tie rods out by using slip on/bolt on rack end spacer to make the tie rod(rack end pivot to tie rod end pivot) the same length as lca bolt to bj AS SEEN FROM BEHIND. Like in the 'behind' part of the picture, not the top view with straight steering, I drew that wrong. It should be like this.
http://www.ae86drivingclub.com.au/dcimages/2/0/2/5/68860.jpg

[bigm]

Yep Pretty much exactly what i was thinking thanks Ken :)

the only thing i dont understand is how the distance between the tie roe end and the LCA balljoint change with adjustment of the caster rod, since they are fixed in place due to the steering knuckle.

This leads to one more question. Would there be any downside to mounting the rack higher and mounting the Ball joint ON TOP of the steering arm, the reason i ask is that currently the balljoint fouls on the LCA, but i am making new LCAs so i am more inclined to notch them to allow the balljoint to stay in standard position and have the rack work as factory (i assume its there for a reason) See pic below for reference


http://www.ae86drivingclub.com.au/dcimages/1/7/2/28454.jpg

[kaibeecee]

it wont make a difference but you'd need a stopper on the LCA. otherwise it would hyper extend.

[bigm]

yep, i had planned on notching and then having an adjustable bolt to prevent binding. since it would be depend on the rack position

[kaibeecee]

do you run RCA's and loads of castor?

bracket would have to be pretty strong to resist bending if it's going to be higher than 30mm. when things get to full lock there's alot of force.

and moving the rack forward doesn't do much with toyota stuff unfortunately.

[bigm]

um maybe 4-5 degrees of caster?

in that was talking if i left the balljoint on the bottom of the steering arm.

i run 33mm RCA's? why do u ask? how do they effect binding?

[Skylar]

Yep Pretty much exactly what i was thinking thanks Ken :)

the only thing i dont understand is how the distance between the tie roe end and the LCA balljoint change with adjustment of the caster rod, since they are fixed in place due to the steering knuckle.

This leads to one more question. Would there be any downside to mounting the rack higher and mounting the Ball joint ON TOP of the steering arm, the reason i ask is that currently the balljoint fouls on the LCA, but i am making new LCAs so i am more inclined to notch them to allow the balljoint to stay in standard position and have the rack work as factory (i assume its there for a reason) See pic below for reference



Point 1: I don't knmow so I went back to where I picked it up from:
http://www.performanceforums.com/forums/showthread.php?t=67204009&highlight=bump+steer

More stuff about bump steer here:
http://www.performanceforums.com/forums/showthread.php?t=67197412&highlight=bumpsteer

Point 2: I don't see why it wouldn't work. Wouldn't it be easier to just cut and shut the steering arms so the tie rod end is further away from the rack end and closer to the wheel? That'll put the tie rod end further away from the lca at the same angle/you'll get more angle before you hit LCA. and that will put the car towards parallel steer if you want to do that.

[Sam-Q]

I do suggest adapting a whole crossmember, it can be a very tricky job and I can expain how I do it with my Celica conversions. What you want to do is measure between the pivot bolts of the lower control arms. Once you have that post it in here and I will let you know what I think. I am guessing xt130 corona

[bigm]

ok cheers sam, ill get onto that over the weekend.