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Alan L's Avatar
 
Join Date: Apr 2006
Location: New Zealand
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torsion bar problem.

My track car has 28mm equivalent hollow rear bars. They are less than a year old, not a lot of track work so far.
The car has dropped in a rear corner - like the bar is set wrong. Spent ages corner balancing it when fitted bars.
If I detach the suspension arms/hubs and just load the spring plate/torsion bar til that corner just lifts off the jackstand, there is more travel in the bar that has the low corner. The distance between the before and after chalk angles is more for the low corner like 26 vs 20mm separation at end of chalk line.
This to me suggests this bar has gone soft?
Is this a reasonable conclusion for a near new bar?
Or is there another explanation?
Alan
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83 SC, 82 930 (track) - Stock except for RarlyL8 race headers, RarlyL8 Zork, K27-7006, 22/28 T bars, 007 Fuel head, short 3&4 gears, NGK AFR, Greddy EBC (on the slippery slope), Wevo engine mounts, ERP rear camber adjust and mono balls, Tarret front monoball camber adjust, Elgin cams, 38mm ported heads, 964 IC. 380rwhp @ 0.8bar Apart from above, bone stock:-)
Old 12-12-2009, 03:43 PM
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I take it everything is tight, no loose nuts or bolts on the stock spring plates? Next I'd look at bushings to see any are soft. After that, I'd suspect the torsion bar. You may need to pull it and have it checked out. Might need to replace both as well?
Old 12-12-2009, 05:21 PM
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I cant find anything loose. Weird.
I have rotated it slightly on the splines and will see what happens. If it keeps going low, I can only assume the bar is wrong.
Alan
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83 SC, 82 930 (track) - Stock except for RarlyL8 race headers, RarlyL8 Zork, K27-7006, 22/28 T bars, 007 Fuel head, short 3&4 gears, NGK AFR, Greddy EBC (on the slippery slope), Wevo engine mounts, ERP rear camber adjust and mono balls, Tarret front monoball camber adjust, Elgin cams, 38mm ported heads, 964 IC. 380rwhp @ 0.8bar Apart from above, bone stock:-)
Old 12-12-2009, 08:17 PM
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Just a few thoughts.

It is odd to have one side slip after a corner balance.

One time I did not get the bolts tight enough and did experience some slipping. It can be at the two larger rear bolts and effect camber or at the two large nuts near he torsion bar end of the arm.

If you are running gas shocks you might check to see if one of them is failing. The shocks can add to the spring rate and if one is leaking it may drop that corner some.

There is always a chance the torsion bar it's self is failing. If you pull it inspect it carefully and inspect the arm carefully to.

You might also inspect the area around where the bolts that hold the side plates on the arms in place for cracks.

Might want to inspect the rear sway bar mounts. It should not have an effect but the rear atachments are a known failure area.

Also, make sure your air pressure is proper for all four wheels. Especially just before a corner ballance.
Old 12-12-2009, 09:35 PM
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He says he disconnected the control arm and isolated the spring plate/radius arm. When he applied floor jack force to the one side, it moved a greater amount for the same force.

He has done a good job of narrowing down the suspect parts/problem area. Perhaps the splines on the inside of the torsion tube are rusty and failing?

Alan, have you pullrd the torsion bar?

Perhaps there was some binding in the suspension when the corner balance was done. Sagging bushings could cause metal rubbing. Putting the car on a lift could extend the suspension beyond the normal range of motion, resulting in parts coming together that normally do not touch. When the car settles out after a drive, this stiction could be overcome and the suspension could then slip back to its normal equilibrium.

I am no expert, though.
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Old 12-13-2009, 01:21 AM
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Each time I did a corner adjust I took it for a short ride over bumps to settle it.
It had held that setting for a few track days. Now it has dropped.
I cant find anything suspect. I pulled the bar out slightly to re index it. It has not broken.
I will settle it again in a day or so and see what happens.
Thanks
Alan
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83 SC, 82 930 (track) - Stock except for RarlyL8 race headers, RarlyL8 Zork, K27-7006, 22/28 T bars, 007 Fuel head, short 3&4 gears, NGK AFR, Greddy EBC (on the slippery slope), Wevo engine mounts, ERP rear camber adjust and mono balls, Tarret front monoball camber adjust, Elgin cams, 38mm ported heads, 964 IC. 380rwhp @ 0.8bar Apart from above, bone stock:-)
Old 12-13-2009, 11:35 AM
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You could alwas pull the T bars and go to coil over's from Rebbel Racing on the rear. This can make it easyer to change rear spring rates and to adjust rear height. They are not very expensive.
Old 12-13-2009, 12:36 PM
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