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Wheel alignment question for track day'ers/racers

 
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AFRICA DEE  



Joined: 16 May 2006
Posts: 48
Location: JOHANNESBURG, SOUTH AFRICA

PostPosted: Wed Nov 01, 2006 8:20 pm    Post subject: Wheel alignment question for track day'ers/racers Reply with quote

My 1980 931 project is coming together now. Motor redone, FMIC is in, etc

The car will only be used for fun, which will include some amateur track days/hill climb type fun.

I have lowered the rear of the car by 40mm (approx 1. 5 inch) ( Torsion bar removal process) and the front as well by installing shorter after market coil overs with 400lbs springs. Was a bargain and had to accept the setup. Front Swaybar is standard.

At rear, coilovers installed with 350lbs springs and standard 14mm swaybar.

The car is now sitting level, but the wheels are pointing in 4 different directions.

I also bought the "special" rear alignment tool. Question? How/where do you apply the tool in the alignment process as we have 4-wheel alignment centres, but no expertise on our cars? So I want to know what I talk about when I approach them. This is obviously to get the general alignment in place. I suppose I can have the car later corner-weighed etc when I have experienced some track days etc.

I also need some spec's for toe-in/castor/camber that will set the car up for fun, but not too race radical. Currently running Dunlop Sports 205/60/15, but will change to 50 profiles when the tyres need to be replaced. Suggestions please.
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1980 924 N/A Ex-931 Track car: My cash guzzler
2004 996 4S: My Weekend plaything
2012 VW POLO GT: My daily commuter
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924RACR  



Joined: 29 Jul 2001
Posts: 8278
Location: Royal Oak, MI, USA

PostPosted: Wed Nov 01, 2006 10:47 pm    Post subject: Reply with quote

Well, I can first recommend on alignment settings that you start with equal camber front/rear, slight toe-in on rear, and slight toe-out on front. These cars tend to be very balanced naturally. Stock alignment as I recall is about 1.5 deg neg camber on rear; how much more than that you might like to run is up to you and others' recommendations. At the upper end, I run 3 degrees front and rear on my racecar.

To adjust rear toe and camber... the eccentric tool goes into the large round hole on the trailing arm, with the smaller pin engaging a slot on the spring plate behind it. When all 3 bolts are loosened (front camber eccentric and two rear lock bolts), the eccentric tool will allow you to move the arm forward or rearwards to change toe. It will also allow you the option to keep the toe relatively unchanged while adjusting the camber eccentric. It takes some practice and a bit of trial-and-error till you get it right. You also don't want to loosen any of the bolts more than absolutely necessary, as when you tighten them the setting can be affected. Measure and measure again!

I wouldn't wait too long to have the car corner-weighted; in fact, since you changed everything including affecting each corner's ride height, your corner weights could be far off - even if the car is sitting level. The car can be really unpleasant to drive in this condition. Better to start from scratch with a proper setting. I'd get it done now. The car will be much more predictable.
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Vaughan Scott
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'79 924 #77 ITB racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype
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924RACR  



Joined: 29 Jul 2001
Posts: 8278
Location: Royal Oak, MI, USA

PostPosted: Wed Nov 01, 2006 10:51 pm    Post subject: Reply with quote

OK, here's a photo to work with.



You can see two very shiny large bolts on the spring plate; these are the height eccentric adjustment and lock bolt (maybe not important on your car any more if you've removed the torsion bars).

Behind that, darker from corrosion and harder to see, you have 3 bolts that are the camber and toe adjustment and lock. The single forward bolt is the camber eccentric; a 27mm wrench on the backside of this will adjust camber once the two rearward bolts, which are just lock bolts, are loosened.

You can also see a hole in the trailing arm roughly in the center of all 3 bolts, and between the dimples; this is where the toe eccentric tool is inserted.

Hope that helps...
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Vaughan Scott
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'79 924 #77 ITB racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype
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Smoothie  



Joined: 01 Jan 2003
Posts: 8030
Location: DE (the one near MD, PA, NJ)

PostPosted: Thu Nov 02, 2006 1:30 am    Post subject: Reply with quote

2 pics starting here - http://pg.photos.yahoo.com/ph/smoothies931pics/detail?.dir=a7d5&.dnm=e941.jpg&.src=ph
(Where it says "pry here" in the first pic - the special tool goes in through the other side of that.)
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"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox
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AFRICA DEE  



Joined: 16 May 2006
Posts: 48
Location: JOHANNESBURG, SOUTH AFRICA

PostPosted: Thu Nov 02, 2006 5:01 pm    Post subject: Reply with quote

Thanks for all the info. and pic's. It will help a lot!!!
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1980 924 N/A Ex-931 Track car: My cash guzzler
2004 996 4S: My Weekend plaything
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