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Lower Control Arm pivot point move


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#1 wildy55

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Posted 20 September 2014 - 12:24 PM

Hey all
So, progressing on well with lowered/uprated suspension for the 240. I've 4 x front 300ZX shocks in place (about an inch shorter in the front and just under two inches shorter in the rear). I've sectioned and welded the struts to suit and have adjustable coilovers to be fitted. I'm running Rota RBs (17x9/9.5). I'm just about to move the LCA pivot on the front crossmember and, reading on the site, 18mm up and 6mm out seems to be the go.
Anyone have any different views/measurements on the new LCA pivot point? Be great to have confirmation before I become Dr Drill...
Cheers in advance

#2 dat2kman

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Posted 20 September 2014 - 12:53 PM

Have seen up and out 15-15, but depending on amount of lowering, alter the Up.
Idea is to get front LCA going downwards at outboard end

I have a Z cross,ember here that is 20-20, it has had additional plating and bracing welded ( rally car)

#3 wildy55

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Posted 21 September 2014 - 06:48 AM

Cheers for your input, Jason. Much appreciated.
Any other figures or suggestions out there?

#4 Six_Shooter

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Posted 24 September 2014 - 12:10 AM

Why is out that people that own S30s are the only ones that want the control atm at an angle? Generally you want the control arm to be level at static ride height. This ensures a minimal and predictable change in camber (and to an extent caster), when the suspension moves up and down from this point.

#5 dat2kman

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Posted 24 September 2014 - 09:35 AM

The dirt and tarmac rally cars, Dato 1600's especially, benefit from having the LCA inner moved.
In a 1600 it is up and out 10-10mm, as their steering geometry is a bit different.
The readon for keeping the outboard ends of the LCA's at a pointed down angle, is to retain as much correct geometry change as pissible when going from lock to lock, during bump and droop.
This is for cars that are lowered.

One way to see the differences is to graph what happens to camber, toe and cadter, when you make one alteration at a time.
This is done by knowing cars static ride height, jacking up, remove spring from strut assy, refitting strut, jacking on a pivoting pad the wheel/strut assy back to static height, fitting a camber/caster guage, taking an extrapolated toe measurement, then you start to turn lock. Back and forth, while raising (bump), and lowering ( droop)

All covered in Freduhn's book, "How to make your car handle"
Yes, another old fadhioned book. Nothing has changed in the cars in a long time, so still very relevant.



#6 Six_Shooter

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Posted 24 September 2014 - 10:20 AM

The dirt and tarmac rally cars, Dato 1600's especially, benefit from having the LCA inner moved.
In a 1600 it is up and out 10-10mm, as their steering geometry is a bit different.
The readon for keeping the outboard ends of the LCA's at a pointed down angle, is to retain as much correct geometry change as pissible when going from lock to lock, during bump and droop.
This is for cars that are lowered.

One way to see the differences is to graph what happens to camber, toe and cadter, when you make one alteration at a time.
This is done by knowing cars static ride height, jacking up, remove spring from strut assy, refitting strut, jacking on a pivoting pad the wheel/strut assy back to static height, fitting a camber/caster guage, taking an extrapolated toe measurement, then you start to turn lock. Back and forth, while raising (bump), and lowering ( droop)

All covered in Freduhn's book, "How to make your car handle"
Yes, another old fadhioned book. Nothing has changed in the cars in a long time, so still very relevant.


Yes, exactly, you mention Datto owners. EVERYONE else in the world wants to keep the (lower) control arm parallel to the ground when at static ride height. If you move the inner pivot of the control arm, you also need to change the steering arm accordingly, so that they both move on the same arc, to keep bump steer at a minimum.

I know on my own car I had considerably more bump steer with a "bumpsteer spacer", than I do without, yes my car is lowered, which is why I installed the bump steer spacers and didn't like the results.

When the (lower) control arm is allowed to point down, the wheel will move out considerably more when the suspension is compressed than when it droops, compared to the control arm was in a neutral position, where compression and droop will have an equal amount of track width change and makes the car more predictable.

#7 Lurch ™

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Posted 24 September 2014 - 10:28 AM

So much miss-information in this thread.

For anyone reading this, consult a suspension specialist that knows about McPherson struts. Take no notice of this thread.

#8 lampy

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Posted 24 September 2014 - 10:59 AM

I agree with lurch. Some very incorrect info in this thread.

Why are you wanting to alter the inner pivot location?

The two normal reasons are roll center adjustment and bump steer adjustment

Moving the inner pivot up and out will radically change the bump steer in usually a bad way. This needs to be corrected by either moving the position of the rack or the outer tie rod height.

To raise the roll center the best way is to install roll center spacers or as incorrectly termed above (bump steer spacers). These do not affect the bump steer but correct the angle of the LCA and therefore the roll center.

Moving the inner pivot is not something to be taken lightly. It is a complex mod and can create a car that handles very bad if you dont correct the unwanted bump steer

#9 dat2kman

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Posted 24 September 2014 - 11:33 AM

Have a chat to Les about what was done to the crossmembers in the 1600's and Bluebirds.
The "better " crossmember was out of the 1968 model.
DMS at Wodonga is pretty cluey on this stuff, as is Al Stean.

#10 peter mc

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Posted 24 September 2014 - 01:17 PM

And lampy gets the gold star  8)

#11 mossy

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Posted 24 September 2014 - 02:02 PM

This needs to be corrected by either moving the position of the rack or the outer tie rod height.


With something like these tie rods? I bought these ages ago but haven't fitted them yet.

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#12 Lurch ™

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Posted 24 September 2014 - 02:17 PM

Yes Mark, but they have to be set up with the correct height.

I easier solution is to bend the steering arm...................

#13 mossy

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Posted 24 September 2014 - 03:54 PM

Sounds cheaper than my option too!

#14 d3c0y

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Posted 24 September 2014 - 04:46 PM

I went your option too. There are other advantages to A/M arms like you can buy both sides still haha.

#15 wildy55

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Posted 26 September 2014 - 11:14 AM

Yes Mark, but they have to be set up with the correct height.

I easier solution is to bend the steering arm...................


Care to expand on this mod?
What and where to bend?
Cheers




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