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Old 05-02-2011   #1
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Rear Beam Axle Alignment

I know this has been covered before but...here's the story. Had four wheel laser alignment done today and was advised the rear axle is 'crabbing'. Here are the figures:

Left rear toe: -0.09 degrees
Right rear toe: +50 degrees

The technician suggested it might be possible to create some 'adjustability' by elongating the holes in the brackets through which the bolts for the rear bushes go, but I don't like that idea one bit.

I was wondering if, instead, it would be possible to insert a shim (drilled with the appropriate holes) betwen the mounting plate on the axle where it attaches to the floopan (by two bolts).

Having said all that, in five years I've had no uneven tyre wear, the car drives straight as a die and handles beautifully...so should I be bovver'd? Answers on a postcard...
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Last edited by Yellow Peril; 05-02-2011 at 20:22.
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Old 05-02-2011   #2
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Re: Rear Beam Axle Alignment

Assume you mean Right rear toe: +0.50 or +0.05. Not +50 degrees.

The four bolt holes in each of the brackets that hold the axle to the floor are already elongated and would allow a small amount of adjustment.

However, if there's no abnormal tyre wear and the car's not pulling to the right, I'd leave it alone.

Putting a shim between the bracket(s) and the floor would only tilt the bracket(s) and axle vertically, not twist it horizontally.
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Last edited by Davren; 05-02-2011 at 21:47.
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Old 06-02-2011   #3
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Re: Rear Beam Axle Alignment

The rear axle is designed to crab slightly to help keep the rear end tight when cornering. A simplified version would be the trucks of a skateboard.

As the axle is solid and offers no adjustment my guess would be damage caused by impact, eg potholes, or component failure, probabely bushes.
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Last edited by Shadeyman; 06-02-2011 at 01:48.
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Old 07-02-2011   #4
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Re: Rear Beam Axle Alignment

Davren, well spotted! The figures should have been:

Left rear toe: -0.09 degrees
Right rear toe: +0.50 degrees.

Shadey, could you explain what you mean by:

'The rear axle is designed to crab slightly to help keep the rear end tight when cornering'

and how this works in practice..? I'm not a skateboarder, so your illustration is lost on me!
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Old 07-02-2011   #5
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Re: Rear Beam Axle Alignment

I've just converted the Stilo eLearn rear axle page to PDF format and attached it to this post. The diagrams will explain it better than I could.

"specially developed for this model and are able to create a toe-in effect on corners to ensure excellent driving stability even under extreme conditions"

The correct alignment of the rear bushes is crucial for them and the the axle to function properly, especially when cornering.

Attached Files
File Type: pdf stilo eLearn - Rear Axle.pdf (33.0 KB, 319 views)
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Last edited by Shadeyman; 07-02-2011 at 10:44.
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Old 07-02-2011   #6
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Re: Rear Beam Axle Alignment

Thanks, that is so helpful. As usual is shows the so-called tracking 'experts' don't know what they're talking about...
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Old 07-02-2011   #7
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Re: Rear Beam Axle Alignment

Having read the doc, I think I understand. It's saying the angle at which the bushes are mounted, relative to the axle, creates a toe-in effect when cornering forces are applied.

However, it still doesn't explain why my toe-in figures (at rest) are different, left to right. Unless, as you said earlier, there's been some deflection of the axle by damage (which I'm not aware of).
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Old 07-02-2011   #8
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Re: Rear Beam Axle Alignment



I hate to throw a damp squib into the post but according to ABCD the fixed static rear toe in on all Stilo models is the same left & right -

3mm +/- 2mm

0.24' +/- 0.16' } degrees
0.40 +/- 0.27 _.._

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Last edited by Peat; 07-02-2011 at 12:39.
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Old 07-02-2011   #9
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Re: Rear Beam Axle Alignment

Quote Originally Posted by Peat View Post


I hate to throw a damp squib into the post but according to ABCD the fixed static rear toe in on all Stilo models is the same left & right -

3mm +/- 2mm

24' +/- 16' } degrees
0.4 +/- 0.27 _.._

Forgive my ignorance, but what's 'ABCD'?
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Old 07-02-2011   #10
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Re: Rear Beam Axle Alignment

Quote Originally Posted by Peat View Post
I hate to throw a damp squib into the post but according to ABCD the fixed static rear toe in on all Stilo models is the same left & right
There's are reasons why its called a "Torsion Axle". One being it allows the "toe in" to vary when cornering.

ABCD?



Quote Originally Posted by Yellow Peril View Post
However, it still doesn't explain why my toe-in figures (at rest) are different, left to right. Unless, as you said earlier, there's been some deflection of the axle by damage (which I'm not aware of).
As the bushes are designed to help the "Toe In" effect, I wonder if installing lowering springs has twisted the bushes just enough to effect the amount of "Toe In" the axle produces prematurely and thats the reason why your getting odd 4 wheel alignment readings?
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Last edited by Shadeyman; 07-02-2011 at 15:58.
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Old 07-02-2011   #11
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Re: Rear Beam Axle Alignment

If itís not causing a problem why worry?
The other thing that comes to mind is how good was the guy doing the tracking, there are a lot of bullsh**ers out there looking for easy money for a job that doesnít need doing.
If it really bothers you I would suggest you at least get a second opinion from a different garage.
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Old 07-02-2011   #12
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Re: Rear Beam Axlehttp://www.fiatforum.com/images/editor/menupop.gif Alignment



Sorry folks it should have read ' Autodata '.

I have it listed as ABCD and wrote that without thinking!
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Old 07-02-2011   #13
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Re: Rear Beam Axle Alignment

Quote Originally Posted by Shadeyman View Post
There's are reasons why its called a "Torsion Axle". One being it allows the "toe in" to vary when cornering.

As the bushes are designed to help the "Toe In" effect, I wonder if installing lowering springs has twisted the bushes just enough to effect the amount of "Toe In" the axle produces prematurely and thats the reason why your getting odd 4 wheel alignment readings?
I'd always assumed that a torsion beam axle was designed to twist to allow one wheel to move vertically more than the other rather than to bend in the middle to allow toe in to vary.
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Old 07-02-2011   #14
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Re: Rear Beam Axle Alignment

Quote Originally Posted by Davren View Post
I'd always assumed that a torsion beam axle was designed to twist to allow one wheel to move vertically more than the other rather than to bend in the middle to allow toe in to vary.
Correct, but the Stilo rear axle is not a normal "Torsion Axle" as is explained in the PDF I attached to post 5.

As I said earlier, there is more than one reason. The clever design of the Stilo axle and its offset bush design does more, allowing the axle to change the "Toe In" and help keep the rear end tight when cornering.
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Old 08-02-2011   #15
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Re: Rear Beam Axle Alignment

The rear axle helps oversteering at high speed. I love the skateboard image you provided, Shadeyman. Turn left or right, and the rear axle comes along to help.
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