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grillhands

Down force weight on jtr trans mount

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During the course of consuming my golden soda, I began to wonder how much down force weight is applied to the jtr mounts that hold the trans. My floors are about a year and half old and I know they'll be fine but Im just wondering what kind of force will the floors be subjected to with my 89 350 sbc with a t56 trans. Thanks.

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You can probably lift the transmission off of the mount with one hand.  It's just mass times inertia.  Hit a bump and there's more down-force, so it depends on how you drive it.

 

There's probably also some up-force.  When you hit the brakes the engine will try to pivot forward on its mounts, creating lift at the transmission tail.  I seem to recall that the early Vega V8 swaps had problems with the engine rocking on its engine mounts.

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i worried about that too. my 280zx had some tranny tunnel reinforcement but didnt feel that did too much. so i added some 1/4in thick steel plate to the floor. had it welded to that tranny support, then welded it to the frame rail. that gave me some great rigidity and i no longer worried about it. not a great pic cause they are painted black already in this pic and they blend in with the bottom of the car.

post-24014-0-43466500-1494260725_thumb.jpg

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It's not just the weight of the transmission on the mounts. Particularly when you shift there is a lot of stress on the transmission mount. I ground mine for clearance with the L6 and ended up snapping it in half shifting to 3rd. 

 

V8, sticky tires, etc, you're going to be putting a lot more force on there than I was with my 240ish whp 6 cyl. Of course, I also weakened the thing by grinding on it...

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What kind of force do you think that shift to 3rd generated?  I can see how the diff nose lifts since the halfshafts are perpendicular, but not really seeing a lifting or dropping force on the tail of the transmission from shifting.  Everything is rotating longitudinally.  And the forward engine mounts should stop the twisting.

 

Just trying to understand the forces.  I mentioned mass and inertia in my reply, relative to bumps.

 

There was a similar topic recently about engines moving forward and hitting the radiator.  But it wasn't clear if they were tilting forward and just damaging the top of the radiator (a clue), or if the whole engine and transmission were moving forward on the same plane.

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I honestly don't know what kind of forces there are there. Would take some actual measurements to clarify. I think the idea is that any part of the drivetrain that can move before the car actually accelerates will do so. Soft motor mounts will squish, mustache and control arm bushings will flex, etc. 

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