Quote:
Originally Posted by Tom
It got much worse after the trans swap from flexing the motor mounts. Just finished changing them, and the vibration is back to when I bought it level of annoying. WTF???
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This is significant, if my line of thinking is correct.
Quote:
Originally Posted by Tom
Need Ideas.
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A couple things you could try, just to see if I'm right:
a) Hang something heavy off the transmission tailshaft. Something big, like an engine block, but still allows you to launch the truck. That will change the resonant frequency of the engine/trans mounting system (which is what you did by refreshing the mounts)*. If it changes the launch shudder, for better or worse, (faster or slower, or change in amplitude) you will at least know if you are barking up the right tree.
b) Make a "junk" one piece shaft. Out of exhaust tubing or junkyard parts or whatever you have laying around. Just strong enough to launch the truck one or two times, to see if the shudder goes away.
c) Play around with the rear axle u joint working angle, aiming for essentially straight during this launch condition (probably not going to work, per Table I attached in the next post; although - this work was done at GCW, if your main complaint is at curb weight then the vehicle might behave differently).
d) Replace the single cardon U joints with CV joints, at both the rear axle and the center bearing (the one at the trans is essentially straight and therefore probably ok). I thought of this just now, only 31 years after it would have been helpful in the resolution of my project. :roll eyes:
If any of these are effective, the next choice would be deciding if you still want to fix it, or if the fixes are painful enough that you'd rather just live with it.
K
*the resonant frequency, which is what the spring/mass system "wants" to vibrate at, is described by the formula attached below. In changing the mounts you affected "k", the spring rate of the lump mass engine/trans system. Increasing the mass, "m", by adding a weight will decrease the resonant frequency, perhaps to a range where it is no longer offensive. That's why you will sometimes see weights hanging off of rear leaf springs, or transmissions, on production vehicles (like Astro/Safari vans, for example).