Worried with those subframe stories

The Gorilla · 07-01-2014, 11:23 AM

Hi,

Yes, Bending and Shear are two different
load / Stress factors, but the 'bolt head' that holds
the subframe to its fixing point is approx 60mm
down from where the bolt is secured [depth of subframe bush]

The original bolt is not held at the top but only
by a threaded section in the tube just above the
surface of the lower skin where the bush/subframe is clamped
up to.

Hence when the subframe starts moving around [vibration initially]
via lateral forces due to the elongation in the
bush alloy insert, this then side ways motion is what is
causing the bolt/fixing to start tearing via a pivoting pendulum
motion at the sheet metal, which over time induces the
stress cracks.

Hence, one force shear, when transmitted via
the pivoting penduliam actions of the bolt is then causing
tear, ie the sheet fatigue.

If the main subframe fixing Bolts were fixed at the top also
and the bolt had a alloy over tube acting as the dowel, then the
shear load on its own is unable move the bolt which is then
not only secured in two places, top and bottom, to prevent
pivotal pendulum type movement but it also has a much
larger surface of clamp which also assist in deflecting load
forces via the alloy spacer around the bolt, being absorbed
correctly into the bush.

The combnation of these additional factors would
mean that the M12 H/T bolt is then performing in
true shear loads only, and any load deflection would
then be loaded into the alloy 'dowel' and absorbed
by the bush as it was originally designed to do.

Its almost be almost identical to what Mercedes did on the
190 rear subframe and while many Merc 190 rear
subframe bushes have been replaced [proves it works well]
I have never herad of or seen a Merc 190 subframe ripping
out its subframe chassis mounts or cause any metal
fatigue or tears other than age corrosion.

Regards,

The Gorilla.

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07-01-2014, 11:23 AM	#33
The Gorilla S5, Sport Off, DSC M-track Join Date: Apr 2008 Posts: 740 Casino cash: $14401	Hi, Yes, Bending and Shear are two different load / Stress factors, but the 'bolt head' that holds the subframe to its fixing point is approx 60mm down from where the bolt is secured [depth of subframe bush] The original bolt is not held at the top but only by a threaded section in the tube just above the surface of the lower skin where the bush/subframe is clamped up to. Hence when the subframe starts moving around [vibration initially] via lateral forces due to the elongation in the bush alloy insert, this then side ways motion is what is causing the bolt/fixing to start tearing via a pivoting pendulum motion at the sheet metal, which over time induces the stress cracks. Hence, one force shear, when transmitted via the pivoting penduliam actions of the bolt is then causing tear, ie the sheet fatigue. If the main subframe fixing Bolts were fixed at the top also and the bolt had a alloy over tube acting as the dowel, then the shear load on its own is unable move the bolt which is then not only secured in two places, top and bottom, to prevent pivotal pendulum type movement but it also has a much larger surface of clamp which also assist in deflecting load forces via the alloy spacer around the bolt, being absorbed correctly into the bush. The combnation of these additional factors would mean that the M12 H/T bolt is then performing in true shear loads only, and any load deflection would then be loaded into the alloy 'dowel' and absorbed by the bush as it was originally designed to do. Its almost be almost identical to what Mercedes did on the 190 rear subframe and while many Merc 190 rear subframe bushes have been replaced [proves it works well] I have never herad of or seen a Merc 190 subframe ripping out its subframe chassis mounts or cause any metal fatigue or tears other than age corrosion. Regards, The Gorilla.