Steve's Triumph Spitfire 1600
The ongoing saaaaaaga
Transmission Mount:
The Miata transmission was very solidly fixed to the differential with the PPF (Power Plant Frame) which kept the geometry just right. Basically the Engine, Transmission, PPF, and Differential are held to the frame with only the two Engine Mounts and the two Differential Mounts and the unit is complete and rigid. I initially had a little dream of being able to somehow modify that PPF for use in the Spitfire, but there is just no room to do such a thing.
In our application a small Transmission Mount would be required at the back of the Tranny, and each time we fit the engine it seemed an elusive engineering task with the small frame cross member and tub always in the way.
After getting the Drive Train Geometry correct resulting in a higher position than expected for the back of the Transmission, and making some of the other changes that were required, including Parking Brake repositioning further aft, we ended up with the very simple solution of a flat piece of steel across the top of longitudinal frame members. Welding the flat steel to the frame was a bit of a task with the tub on the car, but at least we had some access having cut away a portion of the hump to relocate the Parking Brake Handle. One day if I ever pull the tub I'll tidy up that bracket.
We sandwiched some stiff rubber bushings between that flat piece and another we made to go against the Transmission casing otherwise in time it would just mold the bushings around the protrusions where a factory bracket used to go, which would allow movement there.
Also, foreseeing potential for the two screws that go into the bottom of the Transmission from under the bracket eventually backing out with all the torque movement of the assembly and give of the bushings, I wanted to drill a hole in the head of each bolt for locking wire, as done on aircraft. In the end though I just drilled and tapped a hole in the cross-member through which I would put another screw with Lock-Tight and flat piece of steel between flats of the other two bolts to prevent them from backing out. Locking wire is most-definitely a better idea though.
On the Miata the two bolts that attached to the Transmission at that point were not really structural and we had much concern about strength and longevity if we stayed with just those two to secure the aft part of the Transmission.
Although I went one season with no issues I would still like a more robust attachment here. We discussed a strap-system that would go up over the Transmission Output Shaft area and then back down to the bracket attached to the frame but we'll need to give it more thought. Ideas would be appreciated.