transaxle torque reaction

Thanks to Jac Mac, I've discovered a problem with my current oil pan set up regarding the adapter plate - there's no structure below the bottom edge of the block to support the torque reaction of gearbox upon hard acceleration. There used to be a stock LS7 pan, which had a bulk head that supported the adapter plate, but I replaced it so that the pan would not hang below the chassis. So I'm considering a few different options, but happy to hear if anyone else has ideas. A few pics looking at the back of the oil pan/adapter plate interface, facing the back of the car

On the right side of the car (true), install a piece of angle aluminum, 1"x3"x .25" thick, and tie it into the first and third pan rail bolt (counting from back)

On left side, 1"x3.75"x.25" with a 2.75" high relief cut at the back of the section to clear the remote oil filter lines, tie into 3rd and 4th pan rail bolts
utilize trans mounting stud lock nut location by installing a steel fork in its place, run rod end/rod/rod end to a bracket located at 3rd and 4th pan rail bolts.

There's obviously a torque reaction from engine braking, but my feeling is that it is not significant enough to warrant bolting the support into the adaptor place. The left side of the car is the problem area, with the oil lines. Using the stud location, space gets a little tight, but it maintains full integrity. Using the angle section provides a little more space, is easily removed for oil line removal. But there's less structure provided since it has to be relieved to clear the lines. Some integrity could be restored by bolting in a bridge between the two pieces of angle section.

Any criticisms or ideas?



Terry Oxandale

Skinny Man
Not sure I understand your problem Tom, BUT, this is my approach to what I think you are talking about. I mounted my drivetrain as six point, but they are all hard (solid) mounts. two at the normal engine mounting points on the side of the block, two (each side) of the 3/4" adapter plate, and then a single wide mount at the end of the transaxle. Chassis framing was triangulated from front mount to the rear mount to address any frame flexing that may transfer into the drivetrain pieces.
HI Terry,

Thanks for your thoughts. To recap, when you stand on the gas, the junction between the transaxle and the engine block is subject to a large bending moment ie like breaking the engine/gearbox over your knee, right at the junction. If your motor is delivering all 400+ foot pounds and you are in first gear, you are basically delivering 400x2.5 (first gear ratio)x3.5 (final drive ratio, so about 3500 ft/lbs of bending moment.If the adapter plate is unsupported below the bottom of the block, there's basically a 6" lever arm dealing with that torque, allowing the input shaft of the transaxle to push radially against the pilot bearing - a load it isn't designed to cope with. Bad all the way around for all the bearings. I

Your set up deals with this by hard mounting the adapter plate in the middle, along with all the other hard mounts. My set up is bush mounted, so they can move around and reduce vibration. I'll probably try my method first, and if i run into bearing problems, I'll hard mount everything the way you have - thanks for the suggestion, there's more than one way to skin the cat.

Terry Oxandale

Skinny Man
Got it. Well then, my last comment would be that I have never found any vibration issues with the hard-mounting philosophy. I've never had issues with mirror clarity, instrumentation, loosing of nuts/bolts, or any uncomfortable (or even noticeable) vibration. This is the second car I've done this with, learning from the first one (stroked 351W) that these vibration concerns may be overplayed.