Bumpsteer spacers

[blitzkraig]

I think I'm going to drill the new holes in the crossmember by the JTR measurements. So once I do this, will I still need the spacers or will the rearrangement take care of everything? Thanks

oops, someone else hit the submit button before I did:stupid:

[2ManyZs]

You won't need the spacers if you re-drill the mounting holes. The spacers serve to lower the outer end of the control arm to make it parallel with the ground (when using shorter springs the bottom of the strut housing is raised) which puts the roll center back where it should be. By raising the inner pivot point you are doing the same thing. By moving the pivot point out on the crossmember you are then adding negative camber by pushing the bottom of the strut out away form the pivot.

Either way works, and it does the same thing... however, using the spacers and either camber plates or adjustable control arm bushings is a lot easier and the car could then be put back to its stock condition if the situation ever arises that you would want to put it back to stock.

[240ZX]

If you did decide to move your steering rack, you would want to lower it instead of raising it but, it's much much easier to raise the front transverse pivot bolts on the crossmember. Much has been discussed about this subject but, the objective is to obtain front suspension geometry that does not induce steering input when bumps or dips are encountered in the road's surface. Hope this helps you out a little.

[240ZX]

It's late in the day so I may have been a little haisty on the steering rack position but the rest of my previous post is OK! Sorry for any confusion!

[drunkenmaster]

Guys,

I am looking at fitting a non standard rack to the Z and the above info is great. If those knowledgable could offer any further advice on positioning of the rack and tierods specifically in relation to bump steer it would be really appreciated.

Diagrams are good too, i have attached a generic cump steer theory one, two stock suspension shots, and a power steering rack conversion shot.

Please scribble on these to highlight design considerations if you can find the time.

Thanks

James

[panchovisa]

Minor point, but might help when communicating with others.

The term CG (center of garavity) has been used often in this thread incorrectly. The term it has been substituted for is "ride height" and or "roll center"

Yes, if you reduce the ride height you will lower the CG, but you can lower the CG without lowering the whole car (just reposition weight lower in the car).

Ride height is fundementaly tied to the suspension geomety , the center of gavity is totally independent of the suspension geometry.

The roll centers (one center for each end of the car) is related to how all the angles, distances, etc of the geometry produce an axis of roll from front to rear.

Just helping to clean up the terms for everyone.

[drunkenmaster]

Just to add a bit of complication, I have redrilled my crossmember pivot points a year or so ago to combat bumpsteer with the stock rack, is this still useable or should I incorperate the rack position to do the same thing on another stock crossmember I have. I like to keep the variables to a minimum.

What are the main variables to be considered?

If I get the new rack to sit in the same position as the OEM rack, is it just a matter of tie rod length? The angle will be fixed dependant on the rack height right?

I have been wading through so much crap on the internet, I think we need to delete the whole web and start again, and everything I have found seems to reference more "arms" then I can remember on the Z.

Explain the terminology to me in idiots terms as this is all I can remember playing with:

1) Tie rod/steering arm (connected to the rack and pushes or pulls the wheel)

2) A arm/control arm ( holds the stru assembly in a fixed position from the crossmember)

From my limited knowledge, it seems the whole success or failure rests in the position/angle of the tie rod?

Are adjustable tie rods the answer?

and if i am right so far, then this power steering rack conversion pictured below is a bad example due to the tie rod being at a different angle to the control arm?

Therefore the owner should have positioned the rack lower to match the angle of the control arm?

The rack should be fitted with a motor inplace then, I am thinking, otherwise the angles will be off when the suspension is compressed?

phew, that enough for one day

[panchovisa]

Master,

The tie rod is the rod from the inner ball joint at end of steering rack to the steering arm (knuckle) bolted to bottom of strut and also the piece that pin of lower ball joint attaches to. The tie-rod and steering arm are two different pieces.

The front lower control arm attaches at front cross member and the lower ball joint sits on top of it.

The tension and compression rod (TC rod) also attaches to the lower control arm. When the TC rod and lower control arm are considered together as a unit they could be called an A-arm (A shaped, short bar of A being representation of frame of car from front X-member to TC mount pocket)