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 Post subject: Suspension
PostPosted: Tue May 10, 2016 2:42 pm 
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Joined: Tue May 10, 2016 2:31 pm
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Hi There
I have a 1981 Stanza that is very hard to keep on the autocross track
oversteer problems ( Tank Slappers)
Front - Std Stanza set up factory with 1.5 neg camber ( longer lower control arms )
Rear- std coils with Bilstein shockers
Nolathane Bush in rear links
rear diff locked up
No rear sway bar
65 series 14" tyres


any help would be great


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 Post subject: Re: Suspension
PostPosted: Wed May 11, 2016 7:53 pm 
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Joined: Wed Mar 05, 2003 8:38 pm
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Location: straya
Get a rear sway bar


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 Post subject: Re: Suspension
PostPosted: Thu May 12, 2016 5:03 pm 
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Location: CRACE, ACT
You have not said what type of surface you are driving on (Autocross can be on dirt or tarmac) but with a locked diff noting that you are experiencing oversteer, you would have to be on dirt. On tarmac you would experience a very different set of problems, starting with understeer. If you have standard shocks and springs up front and standard sway bar, fitting a rear sway bar as a first step will only induce greater oversteer on the dirt.
As I see it, your current problem arises largely because your rear suspension is soft but over-damped (a consequence of the Bilsteins slowing the action of soft standard rear springs).
Oversteer occurs when (say, suddenly turning left) weight is quickly shifted to the opposite (right) hand side of the vehicle and the outside (right) rear wheel which now has greatest traction tends to drives the car forward and to the left, amplifying your original steering input. In an attempt to make a correction, you suddenly turn the opposite way, and any attempt to correct the see-sawing motion will result in it becoming worse.
The way ahead is counter intuitive (assuming your steering is in good condition): the front springs have to be stiffer, damping rates of the front shock absorbers has to be increased (especially in compression) and a stiffer front sway bar installed to reduce body roll - in combination this will create a bias towards understeer.
Only after upgrading the front suspension would I concentrate on the rear. Next, stiffen up the rear springs - by all means keep the Bilsteins but only if the front shocks have similar or marginally higher damping rate. I suggest front springs should be a bit stiffer than the rears, because of the weight distribution of the Stanza. Only after this, would I suggest fitting a rear sway bar.

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Last edited by AlanDatsomefun on Thu May 12, 2016 5:10 pm, edited 1 time in total.

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 Post subject: Re: Suspension
PostPosted: Thu May 12, 2016 5:08 pm 
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Joined: Sat Oct 30, 2004 2:28 pm
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Location: Melbourne, Australia
Adding a rear swaybar I think will make your oversteer problem worse. If the car was understeering, then I'd add more rear bar.
The locked diff is contributing to the tank slapper aspect. You need to tune your suspension around it.

Lower your front tyre pressure or raise your rear tyre pressure or both.
Firmer front springs would help.
You want a larger front sway bar.

If you have adjustable shocks, the front shocks should be hardened up, while the rears made softer.

For parts and advice, Baz at Datsport in South Aus has a fair bit of experience with Stanza's both on the gravel stuff but also the track, so should be able to sort you out with bolt on goodies and appropriate advice.

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 Post subject: Re: Suspension
PostPosted: Thu May 12, 2016 5:09 pm 
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HAhahaha... Alan beat me to it!

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 Post subject: Re: Suspension
PostPosted: Thu May 12, 2016 5:11 pm 
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AlanDatsomefun wrote:
....As I see it, your current problem arises largely because your rear suspension is soft but over-damped (a consequence of the Bilsteins slowing the action of soft standard rear springs).


Yes. :thumbsup:

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1972 Datsun 1600, S14 SR20DET Engineered (190-210kw @ 15-16psi.)
http://www.ozdat.com/forum/viewtopic.php?t=6579
M35 Axis Autech


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 Post subject: Re: Suspension
PostPosted: Thu May 12, 2016 5:13 pm 
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... and there is something reassuring about experienced "grey beards" having similar thoughts.

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 Post subject: Re: Suspension
PostPosted: Thu May 12, 2016 6:50 pm 
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I wish I could call myself experienced...Might need to grow a beard!

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http://www.ozdat.com/forum/viewtopic.php?t=6579
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