fatbillybob

Hi Gents,

I got my motor out. The rear subass with trans and diff are still in the car. By chance I noticed I can rock the transmission by hand rotating it on the stock tranny mount. I would think this is supposed to be more ridgid. But then I look at the Pfadt replacement and they intentionally make the mount with a pivot point as do another tranny mount copy. So are these mounts supposed to swivel? My head says no but it looks like GM designed them to swivel.

It seems like the motor and trans are tripod stable on 2 engine mounts and 1 transmount and the torque tube keeps the trans from rotating under power.

redtopz

GM designed them to flex, not swivel. They are designed to expand longitudinally with heat and rock side to side slightly also. The C5 Pfadt diff mount includes a lateral strut/brace to minimize the rocking motion and is a nice addition if you install stiffer motor mounts.




There are a variety of combinations and preferences when it comes to motor mounts and diff mounts. My personal preference is not to use full aluminum mounts front or back, but a stiffer polyurethane motor mount combined with the Pfadt diff mount. This combo provides some dampening of engine/tranny vibrations and provides expansion/conraction capabilities for the drivetrain while also minimizing the side to side rocking of the engine as with the stock motor mounts. I found solid aluminum mounts to cause issues with fasteners loosening over time due to harsh vibrations while providing no benefit over poly mounts. I also prefer some flexing in my torque tube which provides forgiveness during occasional mis-shifts or non-ideal rev matching. It all comes down to providing an extra cushion of forgiveness in the system while also smoothing out inputs which can shock the rear tires and cause a sudden loss of grip at the limit. YMMV.