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Re: [T3] Rear End sagging


On 4 Oct 98, at 21:40, Ginger D.&Peter P. wrote:

>     My materials engineering is a bit hazy now, but I believe the
> torsion bar would become stiffer if it sagged.  Like a paper clip that
> is bent too many times gets brittle and then breaks.  I'm wondering if
> this stiffness would be noticable or not.

Permanent deformation changes the point where mor permanent 
deformation will occur, but does not change the "stiffness" (Young's 
modulus.)

>     I guess the main issue is if a sagging bar is about to break.  I
> don't believe so.  A simple bump in the road is bending the bar
> elasticaly (not permanently).  The sagging bar is in effect the first
> permanent bend, and it took 25+ years to happen.  What would really make
> that thing break would be a nick, scratch or rust on the surface.  That
> would be the stress riser to begin propagating a crack.

If the sagging happened all of a sudden, then it is probably the sign 
of a bar that is partially cracked through.  This will eventually 
break and will break sooner if reset, because it will then have more 
range to be stressed through.

I have a VERY good pair of used Squareback swing axle bars if someone 
needs them.  I have had bad experience with some of the aftermarket 
bars.  I replaced the rears in a 914 3 times and they just kept 
breaking.  I don't remember the brand (Sway-A-Way??), but they 
replaced them under warrantee, still the labor was much worse than 
the part cost.

One thing that the OE bars have over the aftermarket ones is that 
they have been prestressed (twisted) so that they are different on L 
and R.  If you mix them up, they will break quickly.  They are marked 
on the ends, so install them correctly.  This goes for front bars as 
well.  All this is covered well in the Bentley manual.

Jim
-
*******************************
Jim Adney, jadney@vwtype3.org
Madison, Wisconsin, USA
*******************************

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